Introduction

Reference: For Systems Operation of the electronic controller, make reference to "Systems Operation for 330, 330 L And 330 LN Excavators Electronic Controller", Form SENR5404.

Reference: For Testing And Adjusting of the hydraulic and electronics systems, make reference to "Testing And Adjusting for 330, 330 L And 330 LN Excavators Hydraulic And Electronic Systems", Form SENR5496.

Reference: For Specifications with illustrations make reference to the Specifications for 330, 330 L And 330 LN Excavators Hydraulic System, Form SENR5493. If the specifications in Form SENR5493 are not the same as in the Systems Operation, look at the printing date on the front cover of each book. Use the specifications in the book with the latest date.

Reference: For Hydraulic schematics, make reference to Hydraulic Schematic for 330, 330 L And 330 LN Excavators, Form SENR5497.

Reference: For Electrical schematics, make reference to the following: Electrical Schematic for 330, 330 L And 330 LN Excavators, Form SENR5499.

Hydraulic Schematic

(1) Swing parking control valve.

(2) Travel motor (left).

(3) Travel motor (right).

(4) Stick cylinder.

(5) Swing motor.

(6) Bucket cylinder.

(7) Boom cylinder.

(8) Stick drift reduction valve.

(9) Swivel.

(10) Pressure switch (implement/swing).

(11) Pressure switch (left travel).

(12) Main control valves.

(13) Boom drift reduction valve.

(14) Main relief valve.

(15) Pressure switch (boom raise).

(16) Pilot control valve.

(17) Pressure switch (right travel).

(18) Pilot control valve.

(19) Solenoid valve (fine control).

(20) Solenoid valve (swing priority).

(21) Solenoid valve (travel speed).

(22) Pilot control valve.

(23) Proportional reducing valve.

(24) Pilot relief valve.

(25) Accumulator.

(26) Upper pump.

(27) Lower pump.

(28) Pilot oil manifold.

(29) Hydraulic activation control valve.

(30) Bypass check valve.

(31) Hydraulic tank.

(32) Shock reducing valve.

(33) Pilot filter.

(34) Pilot pump.

(35) Bypass check valve.

(36) Slow return check valve.

(37) Oil cooler.

(38) Automatic travel speed change valve.

(53) Solenoid valve (fine swing)

Pump Flow And Pressure Control

Introduction

Pump Compartment
(26) Upper pump. (27) Lower pump. (41) Outlet line (upper pump). (42) Housing. (43) Outlet line (lower pump).

This machine is driven and controlled by the following three systems:

1. The Main Hydraulic System (provides oil to the cylinders and motors of the machine).

2. The Pilot Hydraulic System (provides oil to the control circuits).

3. The Electronic Control System (controls outputs from the engine and pump).

The main hydraulic system is driven by main pumps (26) and (27). Pumps (26) and (27) are variable displacement and bent axis piston type pumps. The pumps are identical in performance. Lower pump (27) is directly connected to the engine by a flexible coupling. Pumps (26) and (27) are mechanically connected in parallel through gears. Gear type pilot pump (34), installed in housing (42) is directly connected to lower pump (27) and drives the pilot hydraulic system. All engine output is used for driving these three pumps.

Each of the main pumps delivers approximately 240 liter/min (63 U.S. gpm) of hydraulic oil at no load. The pilot pump delivers approximately 20 liter/min (5.3 U.S. gpm) of hydraulic oil at a load. When a load is placed on the machine, the hydraulic oil is supplied to the main hydraulic circuit.

As the load increases, the main pumps decrease their flow rate. The system is designed to keep the hydraulic horsepower approximately the same as the engine horsepower during system pressure increase or decrease.

Main Control Valve Compartment
(14) Main relief valve. (41) Outlet line (upper pump). (43) Outlet line (lower pump). (44) Right control valve body (operated by upper pump oil). (45) Left control valve body (operated by lower pump oil).

The oil delivered from upper and lower pumps (26) and (27) respectively enters right and left valve bodies (44) and (45) of main control valves (12). If no work is being performed, pump oil flows through the control valves and returns to hydraulic tank (31). Main control valves (12) now send a signal (negative flow control) to each pump causing the respective pump to destroke to minimum output flow.

If an operation is being performed, main control valves (12) direct pump oil to the respective cylinders (boom, bucket and stick) and/or motors (swing and travel). Main control valves (12) contain various valve stems, passages, check valves and orifices which allow an operation to be done by itself or in combination with other operations. The maximum working pressure of the main hydraulic system is restricted to main relief valve (14) setting of 34 300 kPa (5000 psi) during travel operation and 31 400 kPa (4500 psi) during implement/swing operation.

Cab
(46) Control lever (stick and swing). (47) Control lever (boom and bucket). (48) Travel pedal (left). (49) Travel pedal (right).

Pilot pump (34) delivers a constant flow of pressure oil to the pilot circuit. The operating pilot pressure increases to the pilot relief valve setting of 3450 kPa (500 psi).

The pilot circuit has the following three functions:

1. To operate the control valve: When control levers (46) and (47) or pedals (48) and (49) are operated, pilot oil flows to the main control valves through pilot control valves (18), (22) and (16) respectively. This pilot oil pressure shifts the stems in the main control valves allowing the main pump oil to flow to the required circuits of cylinders (4), (6) and (7) and motors (5), (2) and (3).

2. To control pump output: Proportional reducing valve (23) receives an electronic signal and uses the pilot system oil to develop a hydraulic signal pressure. The hydraulic signal pressure goes to the regulators in the main pumps and controls the pump output flow.

3. To create pilot signal pressure in the pilot circuit so the following controls can be achieved:

A. Activate Automatic Engine Speed Control (AEC) system, causing functions to automatically reduce the engine speed when no, or very small hydraulic operation is called for.

B. Change the main relief pressure setting for travel or implement/swing operation.

C. Release the swing motor parking brake.

D. Automatically change travel speed to HIGH or LOW, depending on the machine load.

E. Operate the straight travel control valve to keep the machine traveling straight during a combined operation of travel and implement.

F. Control operations of valves required for easier loading or trenching.

NOTE: For details of the pilot control, see the section, "Pilot Circuit".

Cab
(50) Switch panel. (51) Engine speed dial.

Machine Right Front
(52) Controller.

The electronic control system controls the outputs from the engine and the pump through controller (52). Controller (52) senses the position of the engine governor lever selected by engine speed dial (51). Controller (52) also senses the power mode position selected by the power mode switch located on switch panel (50). Controller (52) processes the information and sends a signal pressure to the pump so the pump can provide an optimum output depending on the machine load and engine speed.

The electronic control system has following four major functions.

1. When a large load is placed on the machine, the system allows the pump to destroke, causing the maximum horsepower available from the engine.

2. Depending on the load placed on the machine, the system controls the output of the pump at an optimum power mode from three different mode settings. This allows the machine to operate at an optimum speed and helps to reduce the fuel consumption.

3. At a no or very small load condition, the system automatically decreases the engine speed to improve the fuel consumption and noise level.

4. The system causes solenoid valves for fine control (19) and swing priority (20) to activate for easier ground surface leveling or vertical finishing of ditch wall surfaces, respectively.

NOTE: For details of the electronic control system, see the separate module "Electric And Electronic System, Systems Operation, Form SENR5404".

Main Pumps

Construction

Main Pumps
(1) Port (upper pump negative flow control pressure). (2) Outlet port (pilot pump). (3) Upper pump. (4) Outlet port (upper pump). (5) Inlet port. (6) Port (power shift pressure). (7) Port (lower pump negative flow control pressure). (8) Lower pump. (9) Outlet port (lower pump). (10) Housing. (11) Pilot pump.

The main pumps consist of upper pump (3) and lower pump (8), coupled in housing (10). The upper and lower pumps are identical in construction, operation and control system.

Oil from the hydraulic tank enters inlet port (5) which is common to both pumps. Each pump delivers oil through its respective outlet port (4) or (9). Pilot pump (11) draws oil through inlet port (5) and delivers oil through outlet port (2).

The power shift pressure for the electronic controller enters the main pump through port (6). The negative flow control pressure from the main control valves enters the main pumps through respective ports (1) and (7).

Main Pumps
(2) Outlet port (pilot pump). (4) Outlet port (upper pump). (5) Inlet port. (9) Outlet port (lower pump). (10) Housing. (11) Pilot pump. (12) Gear (pilot pump). (13) Plate. (14) Pin. (15) Passage (pilot pump). (17) Regulator. (18) Drive shaft (lower pump). (19) Center line. (20) Trunnion. (21) Housing. (22) Center line. (23) Gear (lower pump). (24) Piston. (25) Cylinder. (26) Valve plate. (27) Piston. (28) Gear (upper pump). (29) Shaft (upper pump). (30) Cylinder passage. (31) Inlet passage. (32) Inlet passage. (33) Center hole. (34) Outlet passage. (35) Outlet passage.

The pump is a bent-axis piston type pump. The term bent-axis refers to the angular movement of the piston pump assembly about the point of intersection of center lines (19) and (22). The pump changes its output depending on the angle of cylinder (25).

Drive shaft (18) of the lower pump is directly coupled with the engine flywheel. Gear (23) of drive shaft (18) engages with gear (28) of shaft (29). When drive shaft (18) is driven by the engine flywheel, shaft (29) of the upper pump is driven together through the mechanical linkage of gears (23) and (28). Because the numbers of teeth of gears (23) and (28) are the same, the upper and lower pumps rotate at the same rpm as the engine.

Because gear (23) engages with gear (12) of pilot pump (11), pump (11) rotates with the main pumps.

Pump Operation

The upper and lower pumps are identical in operation. Description is given to the lower pump as a typical example.

Drive shaft (18) is driven by the engine. Drive shaft (18) turns seven pistons (24), causing cylinder (25) to rotate. Cylinder (25) is in contact with valve plate (26). Cylinder (25) rotates on valve plate (26). Cylinder (25) pivots on pin (14). Gear (23) has plate (13) that retains heads of pistons (24), allowing them to swivel in their sockets.

Pump Cover And Valve Plate
(4) Outlet port (upper pump). (5) Inlet port. (9) Outlet port (lower pump). (20) Trunnion. (21) Housing. (26) Valve plate. (31) Inlet passage. (33) Center hole. (35) Outlet passage. (36) Grooves.

Oil from the hydraulic tank goes into pump housing (21) through inlet port (5). The oil goes through inlet passages (32) and (31) in valve plate (26), respectively. The oil then enters cylinder passages (30) of cylinder (25) which are positioned over inlet passage (31). As the cylinder turns, openings of passages (30) in the cylinder rotate to the position of passage (31). Pistons (24) changes its stroke (displacement), depending on the angle of cylinder (25). As the piston moves out of the bore of cylinder (25), it draws oil behind it. As piston moves in the bore, it pushes oil ahead of the piston. The oil that is pushed ahead of the piston goes through passage (30) and then through outlet passage (35) in valve plate (26). The oil then leaves the lower pump through outlet port (9) and goes to the hydraulic circuit.

Valve plate (26) moves on the machined grooves (36) of housing (21). Housing (21) has a circular contour. Center hole (33) of valve plate (26) holds one end of trunnion (20). The other end of the trunnion is held to piston (27) of regulator (17). As piston (27) moves in or out during regulator operation (described later), the cylinder changes its angle because of the mechanical linkage of trunnion (20) and valve plate (26). When valve plate (26) moves in radial direction (C), the cylinder decreases its angle, decreasing the stroke of pistons (24), causing the pump output to decrease. When valve plate (26) moves in radial direction (D), the cylinder increases its angle, increasing the piston stroke for an increase in pump output.

Inlet oil is sealed from the outlet oil by a metal-to-metal seal between the face of valve plate (26) and the face of cylinder (25). On the other side of valve plate (26), the seal is made with the face of the machined groove (36). The sealing faces are made with precision. Protection must be given to these faces during disassembly and assembly.

Valve plate (26) in the lower pump is not the same as valve plate (37) in the upper pump. Use extra care to install plates (26) and (37) in their correct position.

Illustration Of Valve Plates
(26) Valve plate (in lower pump). (37) Valve plate (in upper pump).

Pump Regulator

Regulator (Upper Pump)
(1) Pin. (2) Passage. (3) Passage. (4) Shuttle valve. (5) Passage. (6) Passage. (7) Passage. (8) Housing. (9) Outlet port (upper pump). (10) Outlet passage. (11) Line (upper pump P_N). (12) Passage. (13) Piston. (14) Control piston. (15) Passage. (16) Passage. (17) Passage. (18) Spring. (19) Bushing. (20) Passage. (21) Pin. (22) Spring. (23) Line (P_S). (24) Control piston. (25) Passage. (26) Spring chamber. (27) Spring. (28) Spring. (29) Spring spacer. (30) Spring. (31) Trunnion. (32) Piston. (33) Bolt. (34) Ring. (35) Passage. (36) Cover chamber. (37) Piston chamber. (38) Bolt. (P_D) Pump delivery pressure (upper pump). (P_G) Pilot pump delivery pressure. (P_N) Negative flow control pressure. (P_S) Power shift pressure.

Pump Compartment
(11) Line [upper pump (Pn)]. (23) Line (Ps). (39) Regulator (upper pump). (40) Port (Ps). (41) Regulator (lower pump). (42) Line [lower pump (Pn)]. (43) Outlet line (Pg).

The pump regulator functions as follows:

1. Using the electronic control system, the regulator receives the hydraulic signal pressure [power shift pressure (P_S)] and controls the pump output flow depending on the machine load and engine speed.

2. To keep the horsepower from the engine to the pump constant, the regulator receives the pump delivery pressure P_D. This is called the constant horsepower flow control.

3. When the control levers are in NEUTRAL or in PARTIAL MOVEMENT position, the regulator receives the negative flow control pressure (P_N). Negative flow control pressure (P_N) controls the pump output flow. This is called the negative flow control.

The regulators of the upper and lower pumps are basically identical in construction and operation. Description is given to the upper pump regulator.

Oil from the upper pump and pilot pump flows to regulator (39) as follows:

Oil from the upper pump goes through passages (10) and (7) in housing (8), passage (3) and shuttle valve (4) to passage (2). Oil from the pilot pump goes through passages (16) and (5) and shuttle valve (4) to passage (2). Only the higher pressure of main pump delivery pressure (P_D) or pilot pump delivery pressure (P_G) can go through passage (2).

The pressure through passage (2) separates into the following three paths:

1. One path goes through passage (15) to control piston (14) in the regulator.

2. Another path goes through passage (17) to control piston (24) in the regulator.

3. The third path goes through passages (6) and (35) and cover chamber (36) to piston chamber (37).

Power shift pressure (P_S) goes through line (23) to port (40) which is common to upper and lower pump regulators (39) and (41).

During constant horsepower flow control, the higher pressure of main pump delivery pressure (P_D) or pilot pump delivery pressure (P_G) acts against the shoulder of control piston (14) while power shift pressure (P_S) is acting against the top end face of control piston (14). Control piston (14), pin (21) and piston (24) now shift to control the pump output.

NOTE: For further information, see the section, "Regulator Operation" in this module.

During negative flow control, negative flow control pressure (P_N) from line (11) acts against the top surface of piston (13). Control piston (14) shifts, allowing control piston (24) to move for pump flow control.

Regulator Operation

Constant Horsepower Flow Control (Before Pump Destroke)

Regulator Operation (Before Pump Destroke)
(4) Shuttle valve. (14) Control piston. (15) Passage. (17) Passage. (20) Passage. (21) Pin. (22) Spring. (24) Control piston. (25) Passage. (26) Spring chamber. (27) Spring. (30) Spring. (31) Trunnion. (32) Piston. (33) Bolt. (34) Ring. (35) Passage. (37) Piston chamber. (38) Bolt. (44) Pilot pump. (45) Upper pump. (P_D) Main pump delivery pressure. (P_G) Pilot pump delivery pressure. (P_S) Power shift pressure.

Regulator Operation (Partial)
(14) Control piston. (15) Passage. (17) Passage. (20) Passage. (21) Pin. (22) Spring. (24) Control piston. (25) Passage. (26) Spring chamber. (27) Spring. (46) Shoulder. (47) Top surface. (48) Passage. (49) Passage. (P_D) Main pump delivery pressure. (P_G) Pilot pump delivery pressure. (P_S) Power shift pressure.

When the machine is operating with a low load, the higher main pump delivery pressure (P_D) or pilot pump delivery pressure (P_G) from passage (15) acts on shoulder (46) of control piston (14). Power shift pressure (P_S) from passage (20) acts on top surface (47) of control piston (14). Control piston (14) pushes down against pin (21), trying to move control piston (24) down. Control piston (24) does not move down because the total forces of main pump delivery pressure (P_D), pilot pump delivery pressure (P_G) and power shift pressure (P_S) are less than the combined forces of springs (22), (27) and (30). The force of spring (30) is less than that of spring (27). Spring (30) is compressed before spring (27) is compressed. Passage (48) closes and passage (49) opens making an open connection between passage (25) and spring chamber (26). Tank pressure in spring chamber (26) acts on the bottom surface of ring (34). Main pump delivery pressure (P_D) or pilot pump delivery pressure (P_G) in piston chamber (37) moves piston (32) and ring (34) down until bolt (33) comes in contact with bolt (38). Because of the mechanical linkage of piston (32) and the cylinder through trunnion (31), the cylinder is held at the maximum angle position, allowing the pump to maintain the maximum output flow.

Constant Horsepower Flow Control (After Start Of Pump Destroke)

Regulator Operation (After Start Of Pump Destroke)
(4) Shuttle valve. (14) Control piston. (15) Passage. (17) Passage. (20) Passage. (21) Pin. (22) Spring. (24) Control piston. (25) Passage. (26) Spring chamber. (27) Spring. (28) Spring. (30) Spring. (31) Trunnion. (32) Piston. (34) Ring. (35) Passage. (37) Piston chamber. (44) Pilot pump. (45) Upper pump. (50) Set screw. (P_D) Main pump delivery pressure. (P_S) Power shift pressure.

Regulator Operation (Partial)
(14) Control piston. (15) Passage. (17) Passage. (20) Passage. (22) Spring. (24) Control piston. (25) Passage. (26) Spring chamber. (27) Spring. (46) Shoulder. (47) Top surface. (48) Passage. (49) Passage. (50) Set screw. (P_D) Main pump delivery pressure. (P_S) Power shift pressure.

An increased load on the main pump increases power shift pressure (P_S) and main pump delivery pressure (P_D). (P_D is held more than P_G.)

The combined forces of increased power shift pressure (P_S) and main pump delivery pressure (P_D) act on top surface (47) and shoulder (46) of control piston (14) to overcome the total forces of springs (22) and (30). Control piston (14) pushes down on control piston (24) through pin (21). Passage (49) closes and passage (48) opens, allowing main pump delivery pressure (P_D) from passage (17) to go through passage (25) to the bottom surface of ring (34).

Main pump delivery pressure (P_D) acting on the top surfaces of ring (34), is now supplied to piston chamber (37) through passage (35). Main pump delivery pressure (P_D) is common to both top and bottom surfaces of ring (34). Because the area of ring (34) bottom surface is larger than that of its top surface, ring (34) pushes piston (32) up against the forces of springs (30) and (28). The mechanical linkage of piston (32) and the cylinder through trunnion (31), causes the cylinder to move in its smaller angular direction for pump destroke.

As piston (32) moves up, spring (30) compresses and pushes piston (24) up. Passage (48) closes and passage (49) partially opens, allowing oil to flow from passage (25) to spring chamber (26). Because spring chamber (26) is open to tank pressure, the pressure on the bottom surface of ring (34) becomes less than main pump delivery pressure (P_D). Piston (32) starts to stop upward movement. When the force of main pump delivery pressure (P_D) on the top surface of the ring becomes more than the force on its bottom surface, piston (32) starts to move down. Because of the decreased compression force of spring (30), control piston (24) also starts to move down. Passage (49) now closes and passage (48) partially opens. Piston (32) now starts to move up again because of main pump delivery pressure (P_D) through passage (25) to the bottom surface of the ring.

As main pump delivery pressure (P_D) further increases and compresses spring (27), pistons (24) and (32) operate in the same operating manner as that described above.

When main pump delivery pressure (P_D) is equal to the combined force of springs (28), (30) and (27), piston (32) is in a balanced position and the angle of the cylinder is held at this point. Control piston (24) is now also held at a balanced position by keeping the openings of both passages (48) and (49) slightly opened.

Turning set screw (50) changes the compression force of spring (22) which changes the pump output flow. An increased compression force of the spring increases the pump output flow.

Negative Flow Rate Control

Negative Flow Control Operation (Partial)
(1) Pin. (11) Line [Negative flow control pressure (P_N)]. (12) Port. (13) Piston. (14) Control piston. (17) Passage. (18) Spring. (19) Bushing. (21) Pin. (22) Spring. (24) Control piston. (25) Passage. (26) Spring chamber. (27) Spring. (28) Spring. (30) Spring. (32) Piston. (45) Upper pump. (46) Shoulder. (47) Top surface. (48) Passage. (49) Passage. (51) Passage. (52) Center bypass passage. (53) Negative flow control orifice. (54) Main control valves. (55) Spring spacer. (56) Spring spacer. (P_D) Main pump delivery pressure. (P_G) Pilot pump delivery pressure. (P_N) Negative flow control pressure. (P_S) Power shift pressure.

The rate of oil flow through center bypass passage (52) in main control valves (54) is maximum when all control levers are in NEUTRAL position. When the control levers are partially moved for a fine control operation, part of upper pump oil flows to passage (51), decreasing the rate of oil flow in center bypass passage (52).

The oil flow in center bypass passage (52) is then restricted at negative flow control orifice (53). Negative flow control pressure (P_N) develops in line (11). Modulation [increase or decrease of negative flow control pressure (P_N)] is done depending on the rate of oil flow through center bypass passage (52). Negative flow control pressure (P_N) is maximum when all control levers are in NEUTRAL position, keeping the pump output flow at minimum.

NOTE: For more information of the negative flow control pressure (P_N), see "Control Valve" in this module.

Negative flow control pressure (P_N) in line (11) enters the regulator through port (12) and acts on the top surface of piston (13). Piston (13) tries to move down. Power shift pressure (P_S) acting on top surface (47) of control piston (14) and main pump delivery pressure (P_D) or pilot pump delivery pressure (P_G) acting on shoulder (46) of piston (14) are also acting on the inner surface of bushing (19). Bushing (19) tries to push piston (13) up.

When negative flow control pressure (P_N) acting on piston (13) is greater than the combined forces acting on bushing (19), piston (13) moves down, allowing the negative flow control to function. As piston (13) moves down, bushing (19) is pushed down through pin (1), pushing control piston (14) down. Now the cylinder decreases its angle and destrokes the pump in the same manner as described for the constant horsepower flow control.

When all control levers are in NEUTRAL position [because negative flow control pressure (P_N) is maximum], control piston (14) pushes down against pin (21) moving control piston (24) down, opening passage (48). Now main pump delivery pressure (P_D) or pilot pump delivery pressure (P_G) from passage (17) pushes piston (32) up compressing springs (27), (28) and (30). When the top surface of spring spacer (56) comes in contact with spring spacer (55), control piston (24) is pushed up with piston (32) by the force of main pump delivery pressure (P_D) or pilot pump delivery pressure (P_G) until a balancing condition occurs. Control piston (24) remains in the new balancing position to keep both openings of passages (48) and (49) slightly opened in the same manner as that described for the constant horsepower flow control. The cylinder is now held at the minimum angle position for minimum pump output flow.

When the control levers are partially moved, negative flow control pressure (P_N) gradually decreases its force on piston (13). As the forces of compressed springs (27) and (30) overcome the force of decreased negative flow control pressure (P_N), control piston (24) moves up before spring spacer (56) comes in contact with spring spacer (55). During a fine control operation, the pump output flow is controlled at any rate between minimum and maximum depending on negative flow control pressure (P_N).

When piston (13) moves up due to a lower negative flow control pressure (P_N), the constant horsepower flow control functions.

When main pump delivery pressure (P_D) is very low [less than 3450 kPa (500 psi)] during a fine control operation, piston (32) remains stationary because the low main pump delivery pressure (P_D) cannot overcome the resistance of the cylinder. Now passage (17) and piston chamber (37) are supplied pilot pump delivery pressure (P_G) so that piston (32) can shift.

Pressure/Flow (P-Q) Characteristic Curves

P-Q Characteristic Curves
(1) Point (start of pump destroke). (2) Horsepower characteristics.

The output characteristics of each pump depends on the following two pressures:

1. Pump output circuit pressure.

2. Power shift pressure.

After a pump starts to operate, each pump has a set of pressure/flow (P-Q) characteristic curves. The P-Q curve represents a set of flow rates for different pump circuit pressures. Each point on curve (2) represents the respective flow rate and pressure to maintain pump output horsepower constant.

Hydraulic Schematic Of Main Control Valves

(1) Line relief valve (stick cylinder rod end).

(2) Stick drift reduction valve.

(3) Return passage.

(4) Check valve.

(5) Boom II control valve.

(6) Line relief valve (stick cylinder head end).

(7) Stick I control valve.

(8) Load check valve.

(9) Logic valve.

(10) Swing control valve.

(11) Parallel feeder passage.

(12) Left travel control valve.

(13) Center bypass passage.

(14) Straight travel valve.

(15) Pilot passage.

(16) Main control valves.

(17) Pressure control valve.

(18) Pilot passage.

(19) Pilot passage.

(20) Pressure switch (implement/swing).

(22) Pilot passage.

(23) Right travel control valve.

(24) Center bypass passage.

(25) Attachment control valve.

(26) Load check valve.

(27) Bucket control valve.

(28) Boom I control valve.

(29) Check valve.

(30) Stick II control valve.

(31) Passage.

(32) Passage (lower pump negative flow control).

(33) Orifice (lower pump negative flow control).

(34) Negative flow control relief valve (lower pump).

(35) Negative flow control relief line (lower pump).

(36) Return line.

(37) Passage (upper pump negative flow control).

(38) Orifice (upper pump negative flow control).

(39) Negative flow control line (upper pump).

(40) Line.

(41) Negative flow control relief valve (upper pump).

(42) Boom drift reduction valve.

(43) Line relief valve (boom cylinder head end).

(44) Return passage.

(45) Passage.

(46) Passage.

(47) Pressure control valve.

(48) Main relief valve.

(49) Parallel feeder passage.

(50) Line relief valve (bucket cylinder head end).

(51) Line relief valve (bucket cylinder rod end).

(52) Pilot passage.

(53) Line relief valve (boom cylinder rod end).

(54) Selector valve.

(55) Check valve.

(56) Return line.

(57) Upper pump.

(58) Lower pump.

(59) Pilot pump.

Main Control Valves

Introduction

Main Control Valves(Viewed From The Front)
(5) Boom II control valve. (6) Line relief valve (stick cylinder head end). (7) Stick I control valve. (10) Swing control valve. (12) Left travel control valve. (20) Implement/swing pressure switch. (23) Right travel control valve. (25) Attachment control valve. (27) Bucket control valve. (28) Boom I control valve. (30) Stick II control valve.
(48) Main relief valve. (50) Line relief valve (bucket cylinder head end). (60) Boom raise pressure switch. (61) Right body. (62) Left body.

Main Control Valves(Viewed From The Front)
(1) Line relief valve (stick cylinder rod end). (2) Stick drift reduction valve. (5) Boom II control valve. (6) Line relief valve (stick cylinder head end). (7) Stick I control valve. (10) Swing control valve (12) Left travel control valve. (14) Straight travel control valve. (23) Right travel control valve. (25) Attachment control valve. (27) Bucket control valve. (28) Boom I control valve. (30) Stick II control valve. (48) Main relief valve. (50) Line relief valve (bucket cylinder head end). (51) Line relief valve (bucket cylinder rod end). (53) Line relief valve (boom cylinder rod end). (61) Right body. (62) Left body. (63) Return port. (64) Inlet port (upper pump). (65) Inlet port (lower pump). (66) Return port.

Main control valves (16) are located in the hydraulic system between the pumps and actuators (cylinders and motors). The main control valves control oil flow and pressure from upper pump (57), lower pump (58) and pilot pump (59) so the actuators operate at optimum speed and in the correct direction.

Main Control Valve Bodies

The main control valves consist of right and left bodies (61) and (62). In right body (61), the following control valves are in parallel:

Right travel control valve (23).Attachment control valve (25).Bucket control valve (27).Stick II control valve (30).Boom I control valve (28).

In left body (62), the following control valves are in parallel:

Straight travel control valve (14).Left travel control valve (12).Swing travel control valve (10).Stick I travel control valve (7).Boom II travel control valve (5).

These two bodies are coupled with bolts to make one assembly.

The right body has return port (63). The left body has inlet ports (64) and (65) and return port (66). Upper pump oil flows to inlet port (64). Lower pump oil flows to inlet port (65). Both pump oil flows are controlled by the control valves and supplied to cylinder(s) and/or motor(s) selected for operation.

Return oil from cylinder(s) and/or motor(s) enters the control valves and flows out return ports (63) and (66) and back to the hydraulic tank through the return line.

Each body has other important components as follows.

Right body (61):

1. Boom cylinder rod end line relief valve (53) and bucket cylinder line relief valves (50) and (51) that limit respective circuit pressures.

2. Negative flow control relief valve (41) and negative flow control orifice (38) that function to destroke the main pump when the control levers are in the NEUTRAL position or moved partially.

3. Implement/swing pressure switch (20) that create electric signals for the Automatic Engine Speed Control operation, along with right and left travel pressure switches.

4. Boom raise pressure switch (60) that assures an optimum boom raise speed.

5. Load check valve (26).

Left body (62):

1. Stick cylinder head end line relief valve (6).

2. Negative flow control relief valve (34) and negative flow control orifice (33).

3. Load check valve (8).

NOTE: Major functions of the above components are basically the same as those described in right body (61).

4. Main relief valve (48) that limits the main hydraulic system pressure.

5. Stick drift reduction valve (2) that prevents stick cylinder drift when the main control valves are in neutral position. Stick cylinder rod end line relief valve (1) is located on stick drift reduction valve (2).

In Right Front Of Swing Motor
(42) Boom drift reduction valve. (43) Line relief valve (boom cylinder head end).

Boom cylinder head end line relief valve (43) is located on boom drift reduction valve (42) that is located between the boom control valve and the boom cylinder.

Functions of the main control valves are divided into the following five configurations:

1. Control in the NEUTRAL position with no load placed on cylinders and motors.

2. Individual valve operation.

3. Negative flow control when the control levers are in the NEUTRAL position or moved partially.

4. Load check valve operation to prevent cylinder drift.

5. Relief valve operation to limit circuit pressure.

NOTE: Description on some components that are installed on or in the main control valves will be given separately. Refer to appropriate sections in this module for further information on these components shown below.

1. Implement/swing pressure switch (20): Refer to "Pilot Oil Supply Circuit" section in this module.

2. Boom drift reduction valve (42) and stick drift reduction valve (2): Refer to "Boom, Stick And Bucket Control" section in this module.

3. Straight travel control valve (14): Refer to "Straight Travel Control" section in this module.

Main Control Valve Operation In Neutral Position

Main Control Valves (Neutral position)
(3) Return passage. (5) Boom II control valve. (7) Stick I control valve. (10) Swing control valve. (11) Parallel feeder passage. (12) Left travel control valve. (13) Center bypass passage. (14) Straight travel control valve. (23) Right travel control valve. (24) Center bypass passage. (25) Attachment control valve. (27) Bucket control valve. (28) Boom I control valve. (30) Stick II control valve. (33) Negative flow control orifice. (38) Negative flow control orifice. (44) Return passage. (49) Parallel feeder passage. (61) Right body. (62) Left body. (63) Return port. (64) Inlet port. (65) Inlet port. (66) Return port.

The upper pump supplies oil to right body (61) through inlet port (64), center bypass passage (24) and parallel feeder passage (49). The lower pump supplies oil to left body (62) through inlet port (65), center bypass passage (13) and parallel feeder passage (11).

With the control levers in the NEUTRAL position (no load placed on the machine), upper pump oil flows from inlet port (64) through bypass passage (24), negative flow control orifice (38), return passage (44) and out through return port (63). The oil then flows back to the hydraulic tank. Lower pump oil from inlet port (65) flows through center bypass passage (13), negative flow control orifice (33), return passage (3), return port (66) and back to the hydraulic tank. Oil in parallel feeder passages (49) and (11) supplied from both pumps remains blocked.

Activation of the control levers provides two paths for upper pump oil. One path is from center bypass passage (24) to right travel control valve (23). The other path is from parallel feeder passage (49) to attachment control valve (25), bucket control valve (27) and boom I control valve (28). Activation of any control lever also provides two paths for lower pump oil. One path is from center bypass passage (13) to left travel control valve (12) and stick 1 control valve (7). The other path is from parallel feeder passage (11) to swing control valve (10).

Individual Valve Operation

Bucket Control Valve (Neutral Position)
(1) Bucket control valve. (2) Spring. (3) Port. (4) Port. (5) Pilot port. (6) Pilot port. (7) Passage. (8) Center bypass passage. (9) Load check valve. (10) Return passage. (11) Parallel feeder passage. (12) Line relief valve (bucket cylinder rod end). (13) Line relief valve (bucket cylinder head end). (14) Stem.

The bucket control valve is used as a typical example for describing the operation of individual control valves.

When all of the pilot control valves are in the NEUTRAL position, there is no pilot oil sent to pilot ports (5) and (6) from the pilot control valve. Stem (14) is centered in the Neutral position by the force of spring (2). The upper pump oil goes through center bypass passage (8) to the hydraulic tank.

Bucket Control Valve (Bucket Close Position)
(3) Port. (4) Port. (6) Pilot port. (7) Passage. (8) Center bypass passage. (9) Load check valve. (10) Return passage. (11) Parallel feeder passage. (14) Stem. (15) Passage. (16) Passage.

When the bucket control valve is operated to the Bucket Close position, pilot oil is supplied to port (6) moving stem (14) to the left. This closes center bypass passage (8) and opens passage (16). Passage (15) is now connected to return passage (10).

Upper pump oil in parallel feeder passage (11) flows through load check valve (9), passages (7) and (16) to port (3). The bucket cylinder rod extends, allowing the displaced oil in the rod end to flow to port (4).

Oil from port (4) flows through passage (15) to return passage (10) and back to the hydraulic tank.

Negative Flow Control Signal

Hydraulic Schematic (Partial) (Negative Flow Control)
(1) Center bypass passage. (2) Center bypass passage. (3) Passage. (4) Passage. (5) Orifice. (6) Negative flow control relief valve. (7) Negative flow control line. (8) Orifice. (9) Negative flow control line. (10) Negative flow control relief valve. (11) Return passage. (12) Upper pump. (13) Lower pump.

Main Control Valves (Viewed From Rear)
(7) Negative flow control line. (9) Negative control line.

A negative flow control pressure signal from center bypass passages (1) and (2) occurs during the following instances:

A. When cylinders or motors are not in operation.

B. When fine control of the pilot control valves is needed.

Cross Section Of Stick II Control Valve (Partial) (Negative Flow Control Relief Valve)
(3) Passage. (4) Passage. (8) Orifice. (10) Negative flow control relief valve. (11) Return passage. (14) Plug. (15) Spring. (16) Body. (17) Valve. (P_N) Negative flow control signal pressure.

Oil from upper pump (12) flows through center bypass passage (2), passage (3) and orifice (8) to return passage (11). Oil flow through orifice (8) is restricted causing the pressure in passage (3) to increase. A negative flow control signal pressure (P_N) now goes through passage (4) and negative flow control line (9) to the pump regulator. The negative flow control of the regulator causes the pump to destroke.

Negative flow control relief valve (10) consists of body (16), plug (14), valve (17) and spring (15).

When the oil flow in a center bypass passage suddenly changes, there will be a sudden rise in the negative flow control pressure. To prevent pressure shocks to machine implements, negative flow control relief valve (10) gives a cushion effect by allowing a portion of the oil to flow by valve (17) and through return passage (11).

When all the pilot control valve lever/pedals are in the NEUTRAL position, all of the upper pump oil goes through center bypass passage (2). The oil then goes through orifice (8), return passage (11), and back to the hydraulic tank. Maximum negative flow control pressure (P_N) in passage (3) now goes to the upper pump. The pump cylinder rotates to its minimum angle, causing the upper pump to destroke to provide minimum oil flow.

Typical Cross Section Of Bucket Control Valve (Fine Control Operation)
(2) Center bypass passage. (18) Parallel feeder passage. (19) Port. (20) Stem. (21) Passage. (P) Pilot pressure.

When partial implement operation is started, pilot pressure (P) shifts stem (20) slightly to the left. Pilot pressure (P) partially opens passage (21) and partially closes center bypass passage (2). Part of the upper pump oil from center bypass passage (2) goes to orifice (8). The remainder of the oil goes through parallel feeder passage (18) and passage (21) to port (19). The oil flow in center bypass passage (2) now decreases. The resistance to oil flow through orifice (8) decreases and the negative flow control pressure (P_N) in passage (3) decreases. The upper pump cylinder rotates to a larger angle, causing the upper pump to upstroke increasing the oil flow.

Continuing to full operation moves stem (20) to the left closing center bypass passage (2). There is no oil flow going through passage (3), causing no negative flow control pressure (P_N). The upper pump output is held maximum. Now the upper pump output is controlled by the constant horsepower flow control.

Modulation (increase or decrease) of exact pump output needed is done by inching the control levers. This allows fine control operation of implements for precision work.

The negative flow control works in the same way for lower pump oil through orifice (5).

Load Check Valve

Boom I Control Valve (Boom Raise Position, Load Check Valve Open)
(1) Load check valve. (2) Center bypass passage.

Load check valve (1) has two functions. The first function of load check valve (1) is to prevent a high pressure circuit that is in parallel and in operation at the same time with a lower pressure circuit, from losing oil to the lower pressure circuit. For example, if the bucket cylinder, whose load is light, is moved while the boom cylinders are going up, the high pressure oil of the boom cylinders would want to flow toward the low pressure oil side of the bucket cylinder. If load check valve (1) was not in the circuit, the boom would lower.

The second of load check valve (1) is to prevent the boom from coming down when started at a slow speed. When the boom starts going up at a slow speed, center bypass passage (2) of the boom control valve has partial flow to the hydraulic tank. Without load check valve (1), the pressure oil in the boom cylinders would flow through center bypass passage (2) to the hydraulic tank, causing the boom to come down. Load check valve (1) prevents flow of pressure oil from the head end of the cylinders to the tank.

Main Relief Valve

Cross Section Of Straight Travel Valve And Main Relief Valve
(1) Straight travel valve. (2) Main control valve. (3) Drain passage. (4) Pressure control valve. (5) Passage. (6) Passage. (7) Right travel control valve. (8) Check valve. (9) Check valve. (10) Pilot passage. (11) Passage. (12) Main relief valve. (13) Piston. (14) Line. (15) Line. (16) Line. (17) Upper pump. (18) Lower pump. (19) Pilot pump. (20) Spring. (21) Passage. (22) Passage. (23) Passage. (24) Valve.

Oil from upper and lower pumps (17) and (18) enters main control valves (2) through lines (14) and (15), respectively. Upper and lower pump oil then goes through check valves (8) and (9) to passage (11). Only the higher oil pressure from either the upper or lower pump can go through passage (11) to main relief valve (12).

Oil from pilot pump (19) goes through line (16) to pilot passages (5) and (6). Activation of travel control causes the pressure in passage (6) to increase. Activation of any of implements or swing controls causes the pressure in passage (5) to increase. When travel control is operated alone, pilot oil in passage (6) goes through pressure control valve (4) and pilot passage (10) to piston (13) of main relief valve (12). When implement or swing controls are activated, valve (24) is shifted by the increased pressure in passage (5). The oil acting on piston (13) goes through passage (10) to drain passage (3) and becomes low pressure oil. Now, piston (13) can activate to limit the main relief pressure to 34 300 kPa (5000 psi) when travel control is activated alone. When piston (13) is not activated (during implement or swing operation), the main relief pressure is limited to 31 400 kPa (4550 psi) for any implement operation.

Pressure control valve (4) is located on right travel control valve (7). During travel operation, the oil pressure in passage (5) is less than the force of spring (20), causing valve (24) to move to the right opening passage (23). This allows the pilot oil from passage (6) to flow through passages (23) and (22) to pilot passage (10). When implements and swing controls are activated, the pressure in passage (5) increases and moves valve (24) to the left. Passage (23) now closes and passage (21) opens. Oil in pilot passage (10) now goes through passage (21), drain passage (3) to the pump suction line and becomes low pressure oil.

Main Relief Valve (In Closed Position)
(11) Passage. (25) Valve. (26) Spring chamber. (27) Spring. (28) Valve. (29) Spring. (30) Passage. (31) Orifice. (32) Return passage.

When main pump oil pressure in passage (11) is less than the main relief pressure setting, valve (28) is closed by the force of spring (29). The oil in passage (11) goes through orifice (31) and enters spring chamber (26). Because the pressures in passage (11) and spring chamber (26) are equal, valve (25) shifts to the left by the force of spring (27) and closes passage (30). There is no oil flow from passage (11) to return passage (32).

Main Relief Valve (During Travel Operation With Valve In Open Position)
(10) Pilot passage. (11) Passage. (13) Piston. (25) Valve. (26) Spring chamber. (27) Spring. (28) Valve. (29) Spring. (30) Passage. (31) Orifice. (32) Return passage. (33) Passage. (34) Piston chamber. (35) Adjuster. (36) Passage. (37) Valve chamber.

During travel operation, oil from pilot passage (10) goes through passage (33) to piston chamber (34). Piston (13) moves to the left compressing spring (29), closing valve (28).

As the oil pressure in passage (11) increases to the relief pressure setting for travel circuit, the oil pressure in passage (11) overcomes the force of spring (29) and opens valve (28). The oil in valve chamber (37) goes through passage (36) to return passage (32) and becomes low pressure oil. Now, the oil pressure from passage (11) is decreased at orifice (31). The oil then goes through spring chamber (26) to valve chamber (37). Because of decreased pressure in spring chamber (26), the pressure oil from passage (11) pushes valve (25) to the right against the force of spring (27). Passage (30) now opens, allowing the high pressure oil flow from passage (11) to return passage (32). Pressure adjustment can be made by turning adjuster (35).

Main Relief Valve (During Implement Or Swing Operation With Valve In Open Position)
(10) Pilot passage. (11) Passage. (13) Piston. (25) Valve. (28) Valve. (29) Spring. (32) Return passage. (34) Piston chamber. (38) Plunger.

During an implement or swing operation, there is no oil flow from pilot passage (10) to piston chamber (34). The oil pressure in piston chamber (34) is low. The low oil pressure in piston chamber (34) allows spring (29) to move piston (13) to the right against plunger (38). As piston (13) moves to the right during travel operation, the force of spring (29) acting on valve (28) decreases. The relief valve pressure for implements and swing circuits is now lower than that for travel circuit.

As the oil pressure in passage (11) increases to the relief valve pressure setting for implement or swing circuit, valves (28) and (25) shift to the right allowing oil flow from passage (11) to return passage (32). Pressure adjustment can be made by turning plunger (38).

Line Relief And Makeup Valves

Line relief valve and makeup valves are in the line between each cylinder and its control valve. With an outside force acting against a cylinder (with the control valve in the NEUTRAL position), the pressure in the cylinder and the circuit to the control valve increases. The line relief valve limits the pressure to 33 800 kPa (4900 psi). The line relief valve also operates as a makeup valve.

When an outside force acts on the implement cylinder (with the control valve in the NEUTRAL position), the implement cylinder piston will try to move. A vacuum will occur in the cylinder. The makeup part of the valve sends part of the return oil to the cylinder, removing the vacuum condition.

Line Relief Valve (Closed Position)
(1) Passage. (2) Valve. (3) Valve. (4) Spring chamber. (5) Valve. (6) Spring. (7) Piston. (8) Return passage. (9) Passage.

High pressure oil from the line between each cylinder and its control valve goes through passage (1) and enters the line relief valve. The pressure oil then goes through two grooves (9) in piston (7), and into spring chamber (4). As long as the oil pressure does not exceed the line relief valve pressure setting, valve (5) is kept closed by the force of spring (6). This equalizes the pressure in passage (1) and spring chamber (4). Because there is more surface area on the spring chamber side of valves (2) and (3) than on the cylinder passage side, both valves are shifted all the way to the left and held in position. The oil flow from passage (1) remains blocked to passage (9).

Line Relief Valve (Open Position)
(1) Passage. (3) Valve. (4) Spring chamber. (5) Valve. (6) Spring. (7) Piston. (8) Return passage. (9) Passage. (10) Valve chamber. (11) Passage. (12) Passage.

As oil pressure in passage (1) increases to the relief setting, valve (5) shifts to the right (open position) against the force of spring (6). The oil from valve chamber (10) now goes through passage (12) to return passage (8). The oil pressure in valve chamber (10) decreases. Oil pressure from passage (1) moves piston (7) to the right coming in contact with the left end face of valve (5). The oil from passage (1) now goes around piston (7), and through passage (9). The oil then goes through spring chamber (4) and into valve chamber (10). Because the oil flow is restricted at the outer circumference of piston (7), the oil pressure in spring chamber (4) is decreased. Valve (3) now moves to the right opening passage (11). The oil will now flow from passage (1) to return passage (8).

Line Relief Valve (Makeup Valve In Operation)
(1) Passage. (2) Valve. (3) Valve. (4) Spring chamber. (8) Return passage. (9) Passage. (13) Shoulder.

When oil is lost through the operation of the line relief for the rod end of a cylinder, the oil has to be made up (replaced) in the head end to prevent a vacuum condition.

Because passage (1) is connected to spring chamber (4) through passage (9), a vacuum can occur in passage (1) and spring chamber (4). Pressure oil from return passage (8) acts on shoulder (13) of valve (2). The back side of shoulder (18) receives the negative pressure occurred in spring chamber (4). Valve (2) moves to the right. Now the oil from return passage (8) goes to passage (1) as make-up oil, removing the vacuum condition in passage (1).

Hydraulic Schematic For Pilot Oil

(1) Swing parking brake control valve.

(2) Swing parking brake.

(3) Displacement change valve (left travel).

(4) Displacement change valve (right travel).

(5) Pilot line.

(6) Pilot line.

(7) Stick drift reduction valve.

(8) Pressure switch (implement/swing).

(10) Pilot line.

(11) Parallel feeder passage.

(12) Main control valves.

(13) Pilot line.

(14) Boom drift reduction valve.

(15) Logic valve.

(16) Straight travel valve.

(17) Main relief valve.

(18) Pressure control valve.

(19) Line.

(20) Pilot line.

(21) Pilot line.

(22) Pilot line.

(23) Pilot line.

(24) Pilot line.

(25) Pilot line.

(26) Pilot line.

(27) Pilot line.

(28) Pressure switch (boom raise).

(29) Pilot line.

(30) Pilot line.

(31) Pilot control valve (right/left travel).

(33) Pilot control valve (swing/stick).

(34) Line.

(35) Solenoid valve (fine control).

(36) Solenoid valve (swing priority).

(37) Solenoid valve (travel speed).

(38) Proportional reducing valve.

(39) Pilot control valve (bucket/boom).

(40) Pilot line.

(41) Pilot relief valve.

(42) Passage.

(43) Passage.

(44) Passage.

(45) Passage.

(46) Pilot oil manifold.

(47) Upper pump.

(48) Lower pump.

(49) Pilot pump.

(51) Line.

(52) Hydraulic activation control valve.

(53) Line.

(54) Line.

(55) Pilot filter.

(56) Outlet line.

(57) Automatic travel speed change valve.

(60) Left travel pressure switch.

(61) Right travel pressure switch.

Pilot Oil Supply Circuit

Introduction

Pump Compartment
(38) Proportional reducing valve. (41) Pilot relief valve. (46) Pilot oil manifold. (55) Pilot filter. (56) Outlet line (pilot pump).

Pilot system oil output from pilot pump (49) goes through outlet line (56). The pilot system oil flows through pilot filter (55) and enters pilot oil manifold (46). The pressure of pilot system oil is limited to 3450 kPa (500 psi) by pilot relief valve (41). The oil then goes through passage (45) and separates into the following circuits:

1. Pilot control valves (31), (32), (33) and (39)

2. Proportional reducing valve (38)

3. Automatic travel speed change valve (57) [with travel speed solenoid valve (37) activated]

4. Logic valve (15) [with pressure control valve (18) and swing priority solenoid valve (36) activated]

5. Swing parking brake (2)

6. Pilot circuits in main control valves (12)

Pilot Control Valve Circuits

Cab (Pilot Control Valves)
(31) Pilot control valve (right/left travel). (33) Pilot control valve (right travel). (33) Pilot control valve (swing and stick). (39) Pilot control valve (boom and bucket).

Viewed From Under Cab Floor
(52) Hydraulic activation control valve.

The pilot control valve is the main component in the pilot system. The pilot oil in passage (45) goes through line (34) to hydraulic activation control valve (52). The pilot oil then goes through lines (50), (51), (53) and (54) to pilot control valves (31), (33) and (39), respectively. When any of pilot control valves (31), (33) and (39) are operated, pilot oil goes to the corresponding main control valves. The pilot pressure oil shifts the stem in the control valve to operate a cylinder and/or motor. This provides easier operation of control levers.

Hydraulic Activation Control Lever (LOCK Position)
(58) Lever.

Hydraulic Activation Control Lever (UNLOCK Position)
(58) Lever.

Hydraulic activation control valve (52) is part of the pilot control valve circuit. When hydraulic activation control lever (58) is placed in the LOCK position, hydraulic activation-control valve (52) is closed, blocking the pilot oil supply to any of pilot control valves. The main control valve stems can not be moved. Hydraulic activation control valve (52) is equipped with a limit switch that allows the starter switch to operate only when lever (58) is in the LOCK position. This prevents any possibility of a sudden movement of machine due to unexpected operation of hydraulic controls.

When lever (58) is in the UNLOCK position, hydraulic activation-control valve (52) is open and allows the pilot oil to go through hydraulic activation-control valve (52) to the respective pilot control valves.

NOTE: For more information, see the section of this manual "Hydraulic Activation Control Valve".

Main Control Valve Compartment (Pilot Lines)
(20) Boom II. (21) Stick I. (23) Swing. (24) Left travel. (25) Right travel. (26) Bucket. (27) Boom I. (29) Stick II.

Pilot oil from pilot control valves goes through the respective pilot lines to ports of control valve(s) selected for operation(s). The pilot oil shifts the stems in the main control valves.

Right Front Of Swing Motor
(13) Pilot line. (14) Boom drift reduction valve.

Front Of Main Control Valves
(6) Pilot line. (7) Stick drift reduction valve.

When the control lever is moved to BOOM LOWER position, oil from pilot control valve (39) goes through pilot line (13) to boom drift reduction valve (14). Boom drift reduction valve (14) shifts, allowing the return oil from the boom cylinder head end to go through boom drift reduction valve (14) to the boom control valve. The boom cylinder now operates for a boom lower operation.

When the control lever is moved to STICK IN position, pilot oil flow from pilot line (6) activates stick drift reduction valve (7) in the same manner as that described for boom drift reduction valve (14). Now the stick cylinder operates for stick IN.

NOTE: For more information on boom and stick drift reduction valves, see the section "Boom And Stick Control".

Main Control Valve Compartment
(28) Pressure switch (boom raise)

When the control lever is moved to FULL BOOM RAISE position with the work mode switch at BOOM PRIORITY MODE position, there is a pilot oil flow from pilot line (27) to pressure switch (boom raise) (28). Pressure switch (boom raise) (28) activates causing fine control solenoid valve (35) to energize. During a combined operation of boom and stick, there is no upper pump oil sent to the stick circuit but all of upper pump oil is used for the boom circuit. Now the boom increases its speed.

Bottom Of Cab Floor
(31) Pilot control valve (right/left travel). (60) Left travel pressure switch. (61) Right travel pressure switch.

Right and left travel pressure switches (61) and (60) are located at the bottom of pilot control valve (right/left travel) (31). The On or Off signal of travel pressure switches (61) and (60) is sent to the electronic controller. The electronic controller processes the signals from travel pressure switches (61) and (60), and signal from implement/swing pressure switch (8) so the automatic engine speed control (AEC) functions. The signals from the travel pressure switches are also used for the electronic controller to assure smooth travel operation.

NOTE: For more information on travel pressure switches (60) and (61), see the separate "Systems Operation module, Electric And Electronic Systems, Form 5404".

Proportional Reducing Valve Circuit

Pilot Oil Manifold Compartment
(38) Proportional reducing valve. (40) Pilot line (power shift pressure).

Part of the pilot pump oil in passage (45) goes through passage (44) to proportional reducing valve (38). Proportional reducing valve (38) continuously receives an electrical signal from the electronic controller. Proportional reducing valve (38) changes the pilot oil sent from passage (44) into a hydraulic signal (power shift pressure). The hydraulic signal goes through pilot line (40) to the regulator of the main pump, controlling the pump output.

NOTE: For more information, see the separate Systems Operation module, "Electric and Electronic Systems", Form SENR5494.

Automatic Travel Speed Change Valve Circuit

Pilot Oil Manifold Compartment
(37) Solenoid valve (travel speed). (57) Automatic travel speed change valve.

Right Console
(59) Travel speed switch.

The automatic travel speed change valve circuit activates only when travel speed switch (59) is in the AUTOMATIC TRAVEL SPEED MODE [HIGH (rabbit sign)] position. Moving travel speed switch (59) to AUTOMATIC TRAVEL SPEED position energizes travel speed solenoid valve (37). Part of pilot oil in passage (45) goes through passage (43) to travel speed solenoid valve (37). With a smaller travel load placed on the machine, automatic travel speed change valve (57) remains open. The oil now flows through automatic travel speed change valve (57) and pilot line (10) to displacement change valves (3) and (4) in the left and right travel motors. The travel motors now operate at HIGH speed. As the travel load increases to a certain range, automatic travel speed change valve (57) automatically changes the travel speed to LOW.

NOTE: For more information, see the section, "Travel Control".

Logic Valve Circuit

Main Control Valve Compartment
(18) Pressure control valve. (22) Pilot line.

The logic valve circuit operates during combined loading operation involving boom, stick and swing.

Part of pilot oil from passage (45) goes through passage (42), swing priority solenoid valve (36) and pilot line (22) to pressure control valve (18). This opens logic valve (15), allowing the swing and stick circuits to share the lower pump oil from parallel feeder passage (11) for adequate swing and stick movements relative to boom movement.

NOTE: For more information, see the section, "Loading Operation".

Swing Parking Brake Release Circuit

Swing Motor
(1) Swing parking brake control valve. (5) Pilot line. (19) Line.

The swing parking brake release circuit functions to release the swing parking brake during implements and/or swing operation. Part of pilot oil in passage (45) goes through line (19) to swing parking brake control valve (1). During operation, the pilot pressure oil in pilot line (8) keeps swing parking brake control valve (1) open. The pilot pressure oil goes to swing parking brake (2) and releases the parking brake.

NOTE: For more information, see the section, "Swing Control".

Pilot Oil Circuits In Main Control Valves

Hydraulic Schematic (Partial) (Pilot Oil Circuit In Main Control Valves)
(1) Swing control valve. (2) Left travel control valve. (3) Swing parking brake control valve. (4) Straight travel control valve. (5) Main relief valve. (6) Pilot passage. (7) Pressure control valve. (8) Pressure switch (implement/swing). (9) Pilot passage. (11) Pilot passage. (12) Right travel control valve. (13) Main control valves. (14) Boom I control valve. (15) Drain passage. (16) Orifice. (17) Orifice. (18) Passage. (19) Passage. (20) Passage. (21) Line. (22) Pilot oil manifold. (23) Upper pump. (24) Pilot pump.

Cross Section Of Right Travel Control Valve
(7) Pressure control valve. (8) Pressure switch (implement/swing). (9) Pilot passage. (10) Pressure switch (travel). (11) Pilot passage. (16) Orifice. (17) Orifice. (21) Line.

Main Control Valve Compartment
(4) Straight travel control valve. (8) Pressure switch (implement/swing). (12) Right travel control valve. (21) Line.

Pilot oil from pilot pump (24) goes through pilot oil manifold (22) and enters main control valves (13) through line (21). The oil flow then divides into two paths. One path goes through orifice (17) to pilot passage (11). The other path goes through orifice (16) and then divides into two oil flows. One oil flow directs to pilot passage (9) which is connected to pressure switch (8) for implement and swing. The other oil flows directly to passage (18). When only the travel control is activated, passage (18) is open to pilot passage (6).

Under this condition, the pilot pressure oil is supplied to the following circuits in the main control valves:

1. Pilot pressure oil in pilot passage (11); The pilot pressure oil from pilot passage (11) is used for main relief valve (5) to restrict the working pressure in the travel circuit.

2. Pilot pressure oil in pilot passage (9); The pilot pressure oil from pilot passage (9) is used for main relief valve (5) to restrict the working pressure in the implement/swings circuits. The pilot pressure oil from passage (9) is also used to activate the automatic engine speed control (AEC) and to release the swing parking brake.

3. Pilot pressure oil in pilot passage (6); The pilot pressure oil from pilot passage (6) is used for straight travel control valve (4) to activate for straight machine travel.

NOTE: For more information on pressure control of main relief valve, swing parking brake release and straight travel valve operation, see sections, "Control Valves,", "Swing Control" and "Straight Travel Control", respectively.

Automatic Engine Speed Control (AEC) Circuit

Hydraulic Schematic (Partial) (Pilot Oil Circuit For Travel Operation)
(2) Left travel control valve. (12) Right travel control valve. (13) Main control valves. (24) Pilot pump. (25) Pilot line (forward left travel). (26) Pilot line (forward right travel). (27) Pilot line (reverse left travel). (28) Pilot control valve(right/left travel). (29) Pilot line(reverse right travel). (30) Hydraulic activation control valve. (31) Left travel pressure switch. (32) Right travel pressure switch.

When all the implements and swing controls are in the NEUTRAL position, the pilot oil in pilot passage (9) goes through pilot passage (19) which is open to all of implement and swing control valves, and then goes to drain line (15). Because the circuit pressure in passage (9) is low, implement/swing pressure switch (8) remains Off. When the travel control is in the NEUTRAL position, the pilot oil pressure in each of pilot lines for forward left travel (25), forward right travel (26), reverse left travel (27) and reverse right travel (29) is low. Both travel pressure switches (31) and (32) remain off.

When all pilot control valves are in the Neutral position, each of pressure switches for implement/swing (8), left travel (31) and right travel (32) sends an Off signal to the electronic controller. When the electronic controller receives the Off signal, it activates for the AEC system to function for an engine speed reduction.

When any of implement and swing controls are operated, the operating control valve blocks oil flow through passage (19), causing a pressure increase in passage (9). The pressure increase turns on implement/swing pressure switch (8). When the travel control is operated, the circuit pressure in pilot line (25), (26), (27) or (29) that is used for the travel operation increases. The pressure increase turns on right or left travel pressure switch (31) or (32).

When the electronic controller receives the On signal from pressure switch (8), (31) or (32), it overrides the AEC function. The engine increases its speed to the governor lever setting.

NOTE: The AEC functions to reduce engine speed as long as the load placed on the machine is very small.

NOTE: For more information, see the separate module, "Electric and Electronic Systems, Systems Operation" Form SENR5494.

Pilot Pump

The pilot pump is a gear type pump and is incorporated in the main pump housing. It is mechanically connected to the main pump in parallel through gears. The pilot pump supplies pressure oil to the pilot system. At full load rpm, the pilot pump output flow is approximately 20 liters/min. (5.3 U.S. gal).

Pilot Filter

Pilot Filter
(1) Pilot filter. (2) Bypass relief valve. (3) Filter element.

Filter element (3) in pilot filter (1) removes contaminants from the pilot oil.

If the oil flow through filter element (3) becomes restricted due to the oil being too cold or too contaminated, the oil bypasses the filter through bypass relief valve (2).

Pilot Manifold Components

Pilot Oil Manifold Compartment
(1) Solenoid valve (fine control). (2) Solenoid valve (swing priority). (3) Solenoid valve (travel speed). (4) Line (from pilot filter). (5) Proportional reducing valve. (6) Accumulator. (7) Line (to hydraulic activation control valve). (8) Pilot oil manifold. (9) Pilot relief valve.

Accumulator And Pilot Relief Valve.

Pilot Oil Manifold (Partial)
(4) Line (to hydraulic activation control valve). (6) Accumulator. (7) Line (from pilot filter). (8) Pilot oil manifold. (9) Pilot relief valve. (11) Check valve. (12) Passage. (14) Gas Chamber. (15) Bladder. (16) Bowl. (17) Oil Chamber. (18) Inlet Port. (29) Passage.

Pilot oil flowing through pilot filter and line (4) enters pilot oil manifold (8) and flows through passage (29) and opens check valve (11). The oil then goes through passage (12) and line (7) to the hydraulic activation control valve. Pilot oil in passage (12) is supplied at both inlets of pilot relief valve (9) and inlet port (18) of accumulator (6).

Accumulator (6) provides oil to the pilot line as makeup oil. During combined operations, the pilot system needs more oil because there is not enough pilot pump oil flow. When lowering implements with the engine stopped, makeup oil supply is provided by the accumulator.

The accumulator stores hydraulic pressure oil by taking advantage of the compressibility of nitrogen gas in gas chamber (14).

The pilot pump oil from inlet port (18) goes into oil chamber (17). The pilot pressure oil pushes against bladder (15) compressing the nitrogen gas in gas chamber (14).

Check valve (11) is located in the passage connected to inlet port (18). The check valve prevents oil from flowing back to passage (29). Accumulator oil goes through line (7) and is used to shift the main control valve stems.

Pilot Relief Valve

Pilot relief valve (9) limits the pressure in the pilot circuit to 3450 kPa (500 psi). Since the flow of oil in the pilot system is minimal, most of the output from the pilot pump goes through the pilot relief valve. Most of the oil needed by the pilot system is used to shift one or more of the stems in the main control valves.

Proportional Reducing Valve

Proportional Reducing Valve
(5) Proportional reducing valve. (19) Solenoid. (20) Valve.

The proportional reducing valve (5) consists of solenoid (19) and valve (20). While the engine is operating, an electrical signal from the electronic controller energizes solenoid (19) which controls valve (20). Valve (20) allows a certain amount of pilot pressure oil through to the pump regulator to control pump output. This pilot pressure to the regulator is called power shift pressure. A decrease in engine speed increases the power shift pressure for a decrease in pump output.

An increase in engine speed decreases the power shift pressure for an increase in pump output.

Cross Section Of Proportional Reducing Valve (Partial) (Signal Current Increase)
(21) Rod. (22) Spool. (23) Passage (power shift pressure). (24) Spring. (25) Passage. (26) Passage (pilot pressure).

A decrease in engine speed increases the signal current to solenoid (19) and increases the magnetic force to rod (21). Rod (21) pushes spool (22) down overcoming the force of spring (24). Now passage (25) opens, allowing oil flow from passage (26) through passage (25). The oil then goes through passage (23) to the pump regulator as power shift pressure.

When the power shift pressure increases, the pump destrokes.

Cross Section Of Proportional Reducing Valve (Partial) (Signal Current Decrease)
(21) Rod. (22) Spool. (23) Passage. (24) Spring. (25) Passage. (27) Passage (to pump suction line). (28) Passage.

An increase in engine speed decreases the signal current to solenoid (19). The magnetic force given to rod (21) is smaller than the force of spring (24), causing rod (21) to moves up. Spool (22) follows rod (21) up, opening passage (28) and closing passage (25). The power shift pressure in passage (23) then vents through passage (28) and out through passage (27) to the pump suction line. The power shift pressure decreases, allowing the pump to upstroke.

The power shift pressure is determined by the relationship between the force given to rod (21) and the force of spring (24).

The power shift pressure decreases if the force on the rod is smaller than the force of the spring (smaller signal current flow to the solenoid).

The power shift pressure increases if the force on the rod is larger than the force of the spring (greater signal current flow to the solenoid).

Solenoid Operated Valves

When a solenoid receives an electrical signal, it energizes and operates the valve section.

There are three solenoid valves mounted on the pilot oil manifold..

1. Fine Control Solenoid Valve

Fine control solenoid valve (1) activates for easier fine control operation.

NOTE: For more information, see the section in this module "Leveling Operation".

2. Swing Priority Solenoid Valve

Swing priority solenoid valve (2) activates for easier trenching operation.

NOTE: For more information, see the section in this module "Trenching Operation".

3. Travel Speed Solenoid Valve

Travel speed solenoid valve (3) activates for automatically changing travel speed from LOW to HIGH.

NOTE: For more information, see the section in this module "Travel Control".

Hydraulic Activation Control Valve

Hydraulic Activation Control Valve (UNLOCK Position)
(1) Return port. (2) Port. (3) Limit switch. (4) Hydraulic activation control valve. (5) Port (pilot control valve for swing and stick). (6) Port (pilot control valve for boom and bucket). (7) Port (pilot control valve for left travel). (8) Port (pilot control valve for right travel). (9) Passage. (10) Passage. (11) Spool. (12) Passage. (13) Return passage.

Section A-A Of Hydraulic Activation Control Valve (4)
(2) Port. (3) Limit switch. (9) Passage. (10) Passage. (11) Spool. (14) Plunger. (15) Notch.

When hydraulic activation control valve (4) is placed in the Unlock position, port (2) is open to passage (9) through passage (10) of spool (11). Pilot pump oil enters hydraulic activation control valve (4) through port (2). The oil then goes through passage (9) and out through ports (5), (6), (7) and (8) to pilot control valves. The oil then activates the main control valves.

Limit switch (3) is located in hydraulic activation control valve (4). When hydraulic activation control valve (4) is in the UNLOCK position, spool (11) in hydraulic activation control valve (4) is held at the position shown in the previous illustration (left side). In this position, plunger (14) of limit switch (3) moves out to the left until its end seats in notch (15). Limit switch (3) is now in the Off position.

When hydraulic activation control valve (4) is in the Lock position, spool (11) turns to move plunger (14) to the right, turning limit switch (3) On. Now the pilot pump oil is blocked (held) between port (2) and passage (10), and passage (12) is connected to return passage (13) of spool (11). With the flow of pilot pump oil blocked to passage (9), return oil from each pilot control valve goes through passages (9), (12) and (13), and out through return port (1) to the pump suction line. Now any activation of the pilot control valve lever/pedals will not activate the main control valves.

The start switch can operate only when limit switch (3) is turned On and hydraulic activation control valve (4) is in the Lock position.

Pilot Control Valve (Implements And Swing)

Cab
(1) Pilot control valve (stick/swing). (2) Pilot control valve (bucket/boom)

Both pilot control valves contain within them four valves. Each of the four valves controls a single machine action. Pilot control valve (1) controls the stick in and out movement and the right and left swing movement. Pilot control valve (2) controls the boom raise and lower movement and bucket open and close movement.

Pilot Control Valve (Implements And Swing)
(1) Control lever. (2) Plate. (3) Rod. (4) Rod. (5) Seat. (6) Metering spring. (7) Spring. (8) Return chamber. (9) Return passage. (10) Return passage. (11) Passage. (12) Passage. (13) Spool. (14) Spool. (15) Port. (16) Passage. (17) Port. (18) Line (from main control valve). (19) Line (to main control valve). (20) Pilot pump.

When control lever (1) is moved to the left, plate (2) tilts to the left. Plate (2) pushes down on rod (3) and seat (5) pushes against the force of metering spring (6) and spring (7). The force of metering spring (6) moves spool (14) down, opening passage (11). The oil can now flow through passages (16) and (11), and out port (15) through line (19) to the main control valve. The pressure oil on the end of the main control valve stem causes it to move for implement and/or swing operation.

The oil at the opposite end of the main control valve stem (for the operation) flows back through port (17), through return passage (10) and into return chamber (8) back to the hydraulic tank.

As long as rod (4) is not pushed down, return passage (10) is open and passage (12) is closed.

Spring (7) provides the necessary force to allow the control levers to return to the NEUTRAL position when released.

When the pilot control lever is moved to the left, metering spring (6) is compressed. The metering spring forces spool (14) to move down. Movement of spool (14) controls the amount of pilot oil pressure that goes through passage (11). Pilot oil passes through passage (11) to the main control valves. The pilot oil sent to the main control valves changes proportionally to the travel distance of the pilot control lever. Movement of the main control valve stem causes a change in oil flow to cylinders and/or motors, proportional to a change in pilot oil pressure. Fine movement of the pilot control lever allows fine control of operation of the cylinders and/or motors.

Modulated Pilot Pressure

Partial Cross Section Of Pilot Control Valve
(3) Rod. (5) Seat. (6) Metering spring. (7) Spring. (9) Return passage. (11) Passage. (14) Spool. (16) Passage. (21) Passage. (D) Diameter [of spool (14) for return passage (9)]. (d) Diameter [of spool (14) for passage (11)]. (E) Shoulder [of spool (14)]. (F) Shoulder [of spool (14)]. (L) Length [of metering spring (6) under compression].

When pilot control lever is moved to the left, rod (3) compresses metering spring (6) through seat (5), moving spool (14) down. Any movement of spool (14), under this condition, controls the pressure of the pilot oil that goes through passage (11) to the main control valves. This allows modulation (up and down) of the pilot pressure to the stem of main control valve for fine control operation of the implement or swing.

When the force of metering spring (6) moves spool (14) down, passage (11) opens, as shown in Fig. A. Part of the pilot oil can go through passage (21) and out to the main control valve, moving the stem only part of its travel distance against the force of its spring. This causes a slight increase in pressure which works against shoulders (E) and (F) of spool (14). Because the area of shoulder (E) is larger than that of shoulder (F), spool (14) moves up a small amount of its travel distance against the force of metering spring (6). Return passage (9) partially opens and passage (11) is closed, as shown in Fig. B.

Part of the oil in passage (21) goes out through return passage (9) causing a slight decrease in pressure in passage (21).

When the oil pressure acting on spool (14) is less than the force of metering spring (6), spool (14) returns to its position in Fig. A.

Spool (14) modulates (shift up and down) in a balanced condition between the pressure in passage (21) and the force of metering spring (6).

During modulation (up-and-down movement) of spool (14), a condition can occur that both return passages (9) and (11) are closed at the same time (see Fig. C). This condition provides a certain length (L) of metering spring (6). At this point, the force of the pressure oil in passage (21) and the force of metering spring (6) are equal.

Further downward movement of rod (3) decreases length (L) of metering spring (6) and establishes a new balance between the force of metering spring (6) and the pressure in passage (21). The pressure in passage (21) increases with an increase in the force of metering spring (6).

Pilot oil pressure sent to the main control valves from the pilot control valves increases, directly proportional to the travel distance of the inlet control lever. Movement of the main control valve stem causes an increased oil flow to cylinders and/or motors, proportional to an increased pilot pressure. Fine movement of the pilot control lever allows fine control of operation of the cylinders and/or motors.

The pilot valves for travel operate similar to the pilot valves for the implements and swing. There is a combination control "lever/foot pedal" for each of the left and right travel pilot control valves.

NOTE: For more information on travel pilot control valve operation, see the section, "Travel Control".

Hydraulic Schematic For Return Circuit

(1) Swing motor.

(2) Travel motor.

(3) Drain line.

(4) Makeup line.

(5) Drain line.

(6) Center bypass passage.

(7) Return passage.

(8) Main control valves.

(9) Center bypass passage.

(10) Orifice.

(11) Drain line.

(12) Return line.

(13) Orifice.

(14) Upper pump.

(15) Return line.

(16) Bypass check valve.

(17) Oil cooler.

(18) Bypass check valve.

(19) Hydraulic tank.

(20) Lower pump.

(21) Slow return check valve.

(22) Suction line.

Return Circuit

Introduction

The oil from upper and lower pumps (14) and (20) enters main control valves (8) and then flows as follows:

1. With no load placed on the machine;

a. The upper pump oil goes through center bypass passage (9) and orifice (10) to return passage (7).

b. The lower pump oil goes through center bypass passage (6) and orifice (13) to return passage (7).

2. With a load placed on the machine;

a. Return oil from each control valve for travel, swing and implements goes to return passage (7).

The oil in passage (7) then flows as follows.

1. When the oil temperature is very low, most of the return oil goes through return line (15), bypass check valves (16) and (18) and back to hydraulic tank (19). The remainder of the oil goes through return line (12), slow return check valve (21) and oil cooler (17) to hydraulic tank (19).

2. As the oil temperature increases, the rate of oil flow through line (15) decreases and the rate of oil flow through line (12) increases. More return oil passes through slow return check valve (21) to the hydraulic tank.

Case drain oil from swing motor (1) and travel motors (2) goes through respective drain lines (3) and (5), and combines at drain line (11). The oil then returns to hydraulic tank (19).

If a vacuum occurs in the swing motor, makeup line (4) routes part of the oil from line (12) to the motor, eliminating the vacuum condition.

Slow Return Check Valve And Oil Cooler Circuit

Main Control Valve Compartment (Return Circuit)
(4) Makeup line. (8) Main control valves. (12) Return line. (21) Slow return check valve.

Slow return check valve (21) is provided in the downstream side of return line (12). Slow return check valve (21) restricts oil flow, keeping the circuit pressure in return line (12) at approximately 290 kPa (43 psi). This causes part of oil in return line (12) to go to makeup line (4) to remove the vacuum in the swing motor.

NOTE: For more information on the makeup operation, see the section, "Swing Control".

Oil Cooler (Engine Viewed From Left Side) (Return Circuit)
(17) Oil cooler. (23) Line (inlet). (24) Return line (outlet).

Return oil flow from slow return check valve (21) goes through line (23) to oil cooler (17). The oil cooler is bolted to the engine radiator. The oil is cooled and returns to hydraulic tank (19) through return line (24).

Bypass Return Circuit

Rear Of Hydraulic Tank (Return Circuit)
(11) Drain line. (16) Bypass check valve. (18) Bypass check valve. (19) Hydraulic tank. (24) Return line. (25) Air breather.

Bypass Check Valve
(15) Return line. (16) Bypass check valve.

When return oil temperature is very low, resistance to oil flow in return line (15) is high and causes an increase in oil pressure. Factory settings of bypass check valves (16) and (18) are 290 kPa (43 psi) and 200 kPa (28 psi), respectively. When the pressure increases to approximately 490 kPa (72 psi), bypass check valves (16) and (18) open. Valves (16) and (18) are identical in construction.

Most of the return oil directly flows through line (15) and bypass check valves (16) and (18) to hydraulic tank (19). The remaining oil goes through return line (12), slow return check valve (21), oil cooler (17) and return line (24) to hydraulic tank (19). This causes the oil temperature to increase minimizing the pressure loss.

Hydraulic Tank

Hydraulic Tank
(19) Hydraulic tank. (22) Suction line. (26) Filter. (27) Relief valve. (28) Suction filter. (29) Return chamber. (30) Tank chamber. (R) Return oil.

Return oil (R) from return lines (15) and (24) and drain line (11) enters return chamber (29) of hydraulic tank (19). The oil then goes through filter (26) before it enters tank chamber (30). Oil in hydraulic tank (19) goes out through suction filter (28) and enters the pumps through suction line (22).

Air breather (25) is located on the back side of hydraulic tank (21). Air breather (25) prevents an increase or decrease in pressure in hydraulic tank (18) that could occur due to a change in oil level and/or temperature.

Hydraulic Schematic For Boom Raise

(1) Boom cylinders.

(2) Line.

(3) Boom drift reduction valve.

(4) Line.

(5) Valve.

(6) Parallel feeder passage.

(7) Line.

(8) Main control valves.

(9) Port.

(10) Line.

(11) Check valve.

(12) Load check valve.

(13) Boom I control valve.

(14) Port.

(15) Boom II control valve.

(16) Parallel feeder passage.

(17) Return passage.

(18) Port.

(19) Port.

(20) Return line.

(21) Pilot line.

(22) Return line.

(23) Pilot line.

(24) Pilot control valve (bucket and boom).

(25) Pilot line.

(26) Shock reducing valve (boom raise).

(27) Upper pump.

(28) Lower pump.

(29) Pilot pump.

Boom, Bucket And Stick Control

Boom Raise Control

Boom raise operation uses boom I control valve (13) and boom II control valve (15). The boom moves up in High speed when the oil is supplied to the head end of boom cylinders (1) from both upper pump (27) and lower pump (28). The boom moves up in Low speed when oil is supplied only from the upper pump.

Shock reducing valve (26) is provided to give a cushion for the shock loads that can occur at a stop operation of boom raise by slowing down the stem movement of the boom control valve stem.

NOTE: The operation of the shock reducing valve is described in the section of this module "Components In Cylinder Circuits (Shock Reducing Valve)".

Boom drift reduction valve (3) is provided in the line between main control valves (8) and cylinders (1). When all control levers are in the NEUTRAL position, valve (3) stops reverse oil flow from the head end of cylinders (1) to prevent a boom drift.

Boom Raise (High Speed)

Main Control Valve Compartment
(13) Boom I control. (15) Boom II valve.

Oil from upper pump (27) flows through parallel feeder passage (16). Parallel feeder passage (16) supplies oil to boom I control valve (13).

Oil from lower pump (28) flows through parallel feeder passage (6). Parallel feeder passage (6) supplies oil to boom II control valve (15).

When the boom control lever is moved to its FULL RAISE position, the pilot oil in pilot control valve (24) goes through pilot line (25) and shock reducing valve (26) to pilot line (23). The pilot oil flow then divides into two paths. One oil flow goes through port (19) into boom I control valve (13). The other is through pilot line (21) to port (18) of boom II control valve (15).

Boom I Control Valve (Boom Raise Position)
(9) Port. (12) Load check valve. (16) Parallel feeder passage. (17) Return passage. (19) Port. (30) Passage. (31) Passage. (32) Stem. (33) Passage. (34) Passage. (35) Passage. (36) Spring.

The pilot oil flow from port (19) moves stem (32) of boom I control valve (13) to the left against the force of spring (36). The upper pump oil in passage (16) goes through load check valve (12), passage (31) and (35), and out through port (9). The oil then goes through line (10), valve (5) of boom drift reduction valve (3) and line (2) to the head end of boom cylinders (1).

Boom II Control Valve (Boom Raise Position)
(6) Parallel feeder passage. (11) Check valve. (14) Port. (18) Port. (37) Passage. (38) Passage. (39) Stem. (40) Spring.

Pilot oil at port (18) of boom II control valve (15), moves stem (39) to the left against the force of spring (40). Lower pump oil from parallel feeder passage (6) now goes through passages (37), (38) and check valve (11) and out through port (14) to line (7). The oil then combines with the upper pump oil in line (10). The combined pump oil then goes to the head end of boom cylinders (1).

Return oil from the rod end of boom cylinders (1) flows through line (4) to boom I control valve (13). The oil then flows through passage (30), return passage (17) and return lines (20) and (22) to the hydraulic tank.

Boom Raise (Low Speed)

When the boom control lever is moved part way into a boom raise position, boom I control valve (13) and boom II control valve (15) receive only partial pilot oil pressure.

During a low speed boom raise operation, boom I control valve (13) opens and boom II control valve (15) remains closed. The force of spring (36) in boom I control valve (13) is less than the force of spring (40) in boom II control valve (15). Pilot oil pressure opens boom I control valve (13) before boom II control valve (15). Upper pump oil goes to the head end of cylinders (1) from boom 1 control valve (13). Without lower pump oil supply to the head end of boom cylinders (1), the cylinder rod movement for the boom raise is slower.

Hydraulic Schematic For Boom Lower

(1) Boom cylinders.

(2) Line.

(3) Pilot line.

(4) Spool.

(5) Line.

(6) Passage.

(7) Valve.

(8) Boom drift reduction valve.

(9) Pilot line.

(10) Line.

(11) Pilot line.

(12) Port.

(13) Port.

(14) Load check valve.

(15) Center bypass passage.

(16) Boom I control valve.

(17) Check valve (regeneration circuit).

(18) Center bypass passage.

(19) Orifice.

(20) Parallel feeder passage.

(21) Return passage.

(22) Pilot control valve (bucket and boom).

(23) Line.

(24) Drain line.

(25) Shock reducing valve (boom lower).

(26) Upper pump.

(27) Lower pump.

(28) Pilot pump.

Boom Lower Control

Introduction

When the boom is lowered, only the oil from upper pump (26) is supplied to boom cylinder (1) through boom I control valve (16). Shock reducing valve (25) makes a cushion effect for a shock load at the end of boom I valve (16) stem movement for boom lower operation.

Boom I control valve (16) contains a regeneration circuit for check valve (17). When the control lever is moved to the BOOM LOWER position, check valve (17) causes the displaced oil from the head end of cylinders (1) to go to the rod end of boom cylinders (1). During boom lower operation the regeneration circuit allows the oil flow from upper pump (27) to be shared in other implement functions.

Center bypass passage (15) in boom I control valve (16) partially opens, allowing upper pump oil to go through center bypass passage (15) to center bypass passage (18). The oil then goes through line (23) to the upper pump regulator. The negative flow control of upper pump (25) is activated for destroking.

Boom Lower

When the control lever is moved to the BOOM LOWER position, pilot oil in pilot control valve (22) goes through pilot line (9) and then separates into two paths. One path goes through pilot line (11) and enters boom I control valve (16) through port (12). The other path goes through pilot line (3) to spool (4) in boom drift reduction valve (8).

Boom I Control Valve (Boom Lower Position)
(12) Port. (13) Port. (14) Load check valve. (15) Center bypass passage. (17) Check valve. (18) Center bypass passage. (21) Return passage. (29) Passage. (30) Passage. (31) Passage. (32) Passage. (33) Spring. (34) Spring chamber. (35) Passage. (36) Valve. (37) Spring. (38) Passage. (39) Passage. (40) Passage. (41) Passage. (42) Stem. (43) Passage. (44) Passage. (45) Passage. (46) Passage. (47) Return check valve. (48) Spring. (49) Spring.

The pilot oil from port (12) moves stem (42) to the right. Upper pump oil in parallel feeder passage (20) now goes through load check valve (14) and passage (31), and out through port (13). The oil then goes to the rod end of boom cylinders (1) through line (5).

The return oil from the head end of boom cylinders (1) goes through line (2) and into boom drift reduction valve (8). Because spool (4) is shifted by the pilot pressure from line (3), passage (6) is open to drain line (24). The oil pressure acting on the top of valve (7) becomes lower than the circuit pressure in line (2). The lower circuit pressure causes valve (7) to moves up, allowing the oil in line (2) to go through line (10) and into boom I control valve (16). Part of the return oil goes through passages (44) and (45) and back to the hydraulic tank through return passage (21). Now the boom starts lowering.

Because the return oil flow is restricted at passage (45), movement of the boom cylinder rod is slowed down so that the boom can lower at an appropriate speed depending on the flow rate of upper pump oil.

Regeneration Circuit

The remainder of the return oil in passage (44) goes through passage (41) in stem (42) to check valve (17). With stem (42) moved to the right, passage (35) is open to return passage (21), causing oil to flow from spring chamber (34) to return passage (21). As the oil pressure in spring chamber (34) decreases, the oil pressure in passage (41) overcomes the forces of springs (33) and (37), and moves valve (36) and check valve (17) to the left. Both valves are opened, allowing the oil in passage (41) to go through passage (38) and out through passage (29). The oil then goes to the rod end of the boom cylinders. The regeneration circuit of boom I control valve (16) functions to use the return oil from the head end for boom lower operation.

When the boom control lever is returned to the NEUTRAL position, there is no oil supply to port (12). Stem (42) is shifted to the left (neutral position) by spring (49). Passage (43) closes, blocking oil flow from passage (44). Check valve (17) is now closed by the force of spring (37) and valve (36) is moved to the right by the force of spring (33).

Negative Flow Control During Activation Of Regeneration Circuit

The boom cylinder rod end requires less upper pump oil to be supplied to the cylinder due to activation of regeneration circuit for boom lower. Negative flow control is done as follows:

In Full Boom Lower Position

When the boom control lever is moved to the FULL BOOM LOWER position, upper pump oil in center bypass passage (15) goes through partially open passage (32) and passage (40) to center bypass passage (18). Return oil from the head end enters boom I control valve (16) through passage (44). The return oil then goes through fully open passage (43) to passage (41). Part of oil in passage (41) goes through passages (39) and (40) to center bypass passage (18), and combines with the upper pump oil.

The combined oil in center bypass passage (18) goes through line (23), developing negative flow control signal pressure. The negative flow control pressure acts on the upper pump regulator, causing the upper pump to destroke. Now less oil is required for the cylinder rod end due to the function of the regeneration circuit.

In Partial Boom Lower Position

When the boom control lever is partially moved to BOOM LOWER position with stem (42) slightly shifted to the right, passages (30) and (43) are partially open, and passage (45) is closed. Return oil in passage (44) goes through passages (43) and (41) to return check valve (47). Return check valve (47) is opened allowing oil flow through passage (46) to return passage (21).

Upper pump oil in center bypass passage (15) goes through partially open passage (32). [The opening of passage (32), at this time, is larger than when the boom control lever is moved to FULL BOOM LOWER position.] The oil then goes through passage (40) to center bypass passage (18). The return oil in passage (44) goes through partially open passage (43), passages (41), (39) and (40) to center bypass passage (18), and combines with the upper pump oil.

With the appropriate opening of passage (32), optimum amount of combined oil flows through center bypass passage (18). Now the negative flow control pressure destrokes the pump for proper cylinder operation.

Components In Cylinder Circuits

Shock Reducing Valve (For Boom And Stick)

Shock Reducing Valve Block (Viewed From Left Side Of Swing Frame)
(1) Body. (2) Shock reducing valve (stick out). (3) Shock reducing valve (boom lower). (4) Shock reducing valve (boom raise).

Shock Reducing Valve
(5) Flow control valve. (6) Port (pilot control valve). (7) Spring. (8) Spring. (9) Check valve. (10) Orifice. (11) Port (main control valve). (12) Passage. (13) Valve.

Shock reducing valves (2), (3) and (4) are contained in shcok reducing valve body (1). Shock reducing valve body (1) is located on the left side plate of the swing frame. Shock reducing valve (2), (3) and (4) are for stick out, boom lower and boom raise, respectively. These shock reducing valves function to prevent shock loads at the end of cylinder rod movements by restricting the pilot oil flow returning from each control valve.

When the control lever is moved to any position of STICK OUT, BOOM LOWER and BOOM RAISE, the shock reducing valve for operation selected gets pilot oil through port (6). Pilot oil pressure moves valve (13) to the left against the force of spring (7), opening passage (12). Pilot oil now goes out through port (11) to its control valve. Valve (13) functions similar to that for check valve (9).

When the control lever is returned to the NEUTRAL position, the pilot oil in the main control valve returns to port (11). Pilot return pressure oil moves valve (13) to the right against the force of spring (8). Passage (12) now closes allowing the pilot return oil to go through orifice (10) and out through port (6). Valve (13) functions similar to that for flow control valve (5). Because the oil flow is restricted at orifice (10), the oil flows at a lower rate and the stem of the control valve slowly stops at the closed position. The oil flow in the cylinder and its return line slows down which absorbs the shock loads at the end of cylinder rod movement.

Cylinders (Boom, Stick, Bucket)

Cylinders
(1) Boom cylinder. (2) Rod end port. (3) Tube. (4) Rod. (5) Snubber. (6) Piston. (7) Head end port. (8) Stick cylinder. (9) Snubber. (10) Bucket cylinder.

Snubber Operation (Rod Extending)
(5) Snubber. (11) Passage.

When boom cylinders (1) or stick cylinder (8) come close to the end of their extension stroke, passage (11) begins to be restricted by snubber (5). This restriction slows down the movement of the piston rod just before the piston rod reaches the end of its extension stroke.

Snubber Operation (Rod Retracting)
(9) Snubber. (12) Passage.

When stick cylinder (8) comes close to the end of its retraction stroke, passage (12) is restricted by snubber (9). In the same manner as that for extension stroke, the movement of the piston rod slows down. This absorbs the shock load at the end of the rod movement.

Boom Drift Reduction Valve

Boom Raise

Boom Drift Reduction Valve (Boom Raise Position)
(1) Passage. (2) Passage. (3) Port. (4) Boom drift reduction valve. (5) Spring chamber. (6) Spring. (7) Valve. (8) Port. (9) Spool. (10) Passage. (11) Passage. (12) Passage. (13) Spring chamber. (14) Drain line. (15) Port. (16) Pilot line. (17) Port. (18) Passage.

Boom Drift Reduction Valve (Right Front Of Swing Motor)
(4) Boom drift reduction valve. (14) Drain line. (16) Pilot line.

When the boom control lever is moved to the BOOM RAISE position, the oil from boom I and II control valves enters boom drift reduction valve (4) through port (8). The oil then acts on the right end face of valve (7). Because no oil is sent to pilot line (16) from the pilot control valve, spool (9) remains stationary. Pilot line (16) connects passage (1) and port (3) through passages (12), (18), (10), (11) and (2).

With passage (1) connected to port (3), as the pressure of oil at port (8) is more than the force of spring (6), valve (7) moves to the left, compressing spring (6). Oil through port (8) goes to port (3). At the same time, the oil in spring chamber (5) goes through passages (1), (18) and (2) to port (3). Both oil flows through port (3) then go to the head end of the boom cylinders.

Boom Lower

Boom Drift Reduction Valve (Boom Lower Position)
(1) Passage. (3) Port. (4) Boom drift reduction valve. (5) Spring chamber. (7) Valve. (8) Port. (9) Spool. (10) Passage. (11) Passage. (12) Passage. (13) Spring chamber. (14) Drain line. (15) Port. (16) Pilot line. (17) Port. (18) Passage. (19) Cover.

When the control lever is moved to the BOOM LOWER position, pilot oil from the pilot control valve goes through pilot line (16) and into boom drift reduction valve (4) through port (17). The oil then moves spool (9) to the right until it comes in contact with the bottom bore of cover (19). The oil in spring chamber (5) goes through passages (1), (10), (18) and (12) and into spring chamber (13). The oil then goes out through port (15) and goes through drain line (14) to the pump suction line. The oil pressure in chamber (5) now decreases.

Return oil from the boom cylinder head end enters boom drift reduction valve (4) through port (3). Because the oil pressure in spring chamber (5) is low, valve (7) begins to open by moving to the left. The return oil now goes out through port (8) to the boom I control valve.

Bucket Control

When the bucket is operated for CLOSE and DUMP, only the upper pump oil is supplied to the bucket cylinder. When the control lever is moved to the BUCKET CLOSE position, the return oil is restricted by the stem in the bucket control valve. The bucket now operates at an appropriate speed depending on the pump delivery flow.

Hydraulic Schematic For Stick Out

(1) Stick cylinder.

(2) Line.

(3) Pilot line.

(4) Stick drift reduction valve.

(5) Drain line.

(6) Line.

(7) Line.

(8) Valve.

(9) Main control valve.

(10) Line.

(11) Return line.

(12) Passage.

(13) Return passage.

(14) Center bypass passage.

(15) Stick II control valve.

(16) Passage.

(17) Check valve.

(18) Passage.

(19) Center bypass passage.

(20) Passage.

(21) Pilot line.

(22) Boom II control valve.

(23) Passage.

(24) Stick I control valve.

(25) Parallel feeder passage.

(26) Return passage.

(27) Check valve.

(28) Passage.

(29) Selector valve.

(30) Passage.

(31) Check valve.

(32) Pilot line.

(33) Pilot line.

(34) Return line.

(35) Pilot line.

(36) Pilot control valve.

(37) Pilot line.

(38) Solenoid valve (fine control).

(39) Pilot line.

(40) Pilot line.

(41) Pilot line.

(42) Shock reducing valve.

(43) Pilot line.

(44) Upper pump.

(45) Lower pump.

(46) Pilot pump.

Stick Control

Introduction

Main Control Valve Compartment
(15) Stick II. (24) Stick I.

Front Of Main Control Valve
(4) Stick drift reduction valve.

Both Stick Out and In operations use stick I control valve (24) and stick II control valve (15). Stick I control valve (24) and stick II control valve (15) cause the combined oil to flow from upper pump (44) and lower pump (45) to stick cylinder (1).

Shock reducing valve (42) (similar to that for the boom operation) functions to make a cushion for the shock loads at a stop of stick out operation.

Stick drift reduction valve (4) functions similar to that for the boom drift reduction valve. See the section, "Boom Drift Reduction Valve".

Stick Out

When the control lever is moved to the STICK OUT position, pilot oil from pilot control valve (36) goes through pilot line (43) and shock reducing valve (42) to pilot line (40). The oil flow then divides into two paths. One path goes through pilot line (21) and enters stick I control valve (24) shifting its stem. This allows the lower pump oil in center bypass passage (19) to go through load check valve (17), passage (18) and stick I control valve (24) to passage (12). The oil then goes through line (7) and enters stick drift reduction valve (4) opening valve (8). The oil leaves stick drift reduction valve (4) and goes through line (2) to the rod end of the stick cylinder.

The other path from pilot line (40) goes through pilot line (35) and enters stick II control valve (15) shifting its stem. Stick II control valve (15) closes, causing no oil flow from center bypass passage (14) through passage (16) to return passage (26).

Upper pump oil in center bypass passage (14) now goes through check valve (27) and passage (20) to line (10). Upper pump oil in parallel feeder passage (25) goes through selector valve (29) and check valve (31) to line (10). All upper pump oil in line (10) goes through passage (23) and combines with lower pump oil in passage (18). The cylinder now increases its speed.

NOTE: The operation of stick II selector valve (29) will be described later.

Return oil from the stick cylinder head end goes through line (6) and stick I control valve (24) to return passage (13). The return oil then goes back to the hydraulic tank through return lines (11) and (34).

Stick In

When the control lever is moved to the STICK IN position, pilot control valve (36) sends the pilot oil to pilot line (41). The oil flow from line (41) then separates into two oil paths. One path goes through pilot line (33) to stick I control valve (24) shifting its stem. The other path goes through pilot line (37), fine control solenoid valve (38) and pilot line (39), and enters stick II control valve (15) shifting its stem.

In the same manner as that described for Stick Out, lower pump oil goes through center bypass passage (19) to stick I control valve (24). The upper pump oil goes through center bypass passage (14) and parallel feeder passage (25) to line (10) and combines with the lower pump oil in stick I control valve (24). The combined oil then goes through line (6) to the head end of the stick cylinder.

The return oil from the rod end of the stick cylinder goes through line (2), stick drift reduction valve (4) and line (7), and into stick control valve (24). The oil then goes through return passage (13) and return line (11) and back to hydraulic tank. The stick cylinder now operates for Stick In.

NOTE: Operation of stick drift reduction valve (4) will be described in the section, "Boom Lower".

Stick II Control Valve And Selector Valve

Stick II Control Valve
(10) Line. (14) Center bypass passage. (25) Parallel feeder passage. (27) Check valve. (28) Passage. (29) Selector valve. (30) Passage. (31) Check valve. (47) Passage. (48) Passage. (49) Passage. (50) Port. (51) Port. (52) Passage. (53) Stem. (54) Spring. (55) Piston chamber.

Selector valve (29) is installed in stick II control valve (15).

NOTE: Operation of stick II control valve (15) and selector valve (29) is described in the section, "Stick In".

When stem (53) is shifted to the right by the pilot oil flow from port (50), upper pump oil in parallel feeder passage (25) goes through passages (28) to passage (48). The oil in passage (48) then separates into two oil paths. One path goes through check valve (31) to line (10). The other path goes through passages (49) and (30) and into piston chamber (55). The pressure of oil in piston chamber (55) moves selector valve (29) to the left against the force of spring (54). This opens both passage (47) and (49). Now the upper pump oil in passage (28) goes through passages (47) and (49) and combines with each other in passage (48). The combined oil then goes to line (10).

Upper pump oil in center bypass passage (14) goes through check valve (27) and combines with the upper pump oil from parallel feeder passage (25). The combined oil then leaves the stick II control valve and flows to line (10).

When the control lever is moved to the Stick Out position, pilot oil enters the stick II control valve through port (51). The pilot oil goes through passage (52) to act on selector valve (29). Selector valve (29) usually remains shifted to the right by the pilot oil from passage (52) and the force of spring (54) to close the connection between passages (47) and (49). It is very rare that selector valve (29) moves to the left to connect passages (47) and (49) where upper pump oil from parallel feeder passage (25) goes through selector valve (29).

Hydraulic Schematic For Swing Right

(1) Swing parking brake control valve.

(2) Spool.

(3) Pressure reducing valve.

(4) Passage.

(5) Swing parking brake.

(6) Swing motor rotary group.

(7) Swing motor.

(8) Line.

(9) Line.

(10) Pilot line.

(11) Main control valves.

(12) Drain line.

(13) Line.

(14) Return passage.

(15) Load check valve.

(16) Parallel feeder passage.

(17) Pilot passage.

(18) Attachment control valve.

(19) Bucket control valve.

(20) Boom I control valve.

(21) Return line.

(22) Passage.

(23) Stick I control valve.

(24) Passage.

(25) Swing control valve.

(26) Passage.

(27) Orifice.

(28) Pilot passage.

(29) Line.

(30) Line.

(31) Pilot control valve (swing and stick).

(32) Line.

(33) Pilot oil manifold.

(34) Drain line.

(35) Passage.

(36) Upper pump.

(37) Lower pump.

(38) Pilot pump.

(39) Hydraulic tank.

(40) Slow return check valve.

Swing Control

Introduction

Swing motor (7) is driven by pressure oil from lower pump (37). When the swing control lever is moved swing brake (5) is first released, and then swing motor rotary group (6) starts to rotate.

The swing drive reduces the motor speed into two stages and then rotates the upper structure.

Swing Right Operation

Main Control Valve Compartment
(7) Swing motor. (8) Line. (9) Line. (25) Swing control valve.

When the control lever is moved to the SWING RIGHT position, pilot oil from pilot control valve (31) goes through line (13) to swing control valve (25). The stem in swing control valve (25) shifts and opens passages (26) and (24).

The lower pump oil goes through parallel feeder passage (16), load check valve (15), passage (26) and enters swing control valve (25). The oil then goes through passage (24) and line (9) to swing motor rotary group (6).

Return oil from swing motor rotary group (6) goes through line (8) and enters swing control valve (25). The oil now goes through return passage (14) to return line (21). Swing motor rotary group (6) rotates causing the upper structure to swing to the right.

Swing Parking Brake

On Position

Swing Motor Compartment
(1) Swing parking brake control valve. (7) Swing motor. (10) Pilot line. (12) Drain line. (30) Line.

Pilot oil from pilot pump (38) enters pilot oil manifold (33) and goes through passage (35). The pilot oil then separates into two paths and leaves pilot oil manifold (33). One path goes through line (30) and enters swing parking brake control valve (1). The other path goes through line (32) and enters main control valves (11). The oil then goes through orifice (27) and to pilot passage (28). Oil flow through pilot passage (28) is restricted by orifice (27). Part of the pilot oil goes to pilot passage (17) which is a branch of pilot passage (28). The orifice restriction causes an oil pressure decrease in both pilot passages (28) and (17).

With main control valves (11) in the neutral position (except travel control), the control valves for swing (25), stick I (23), attachment (18), bucket (19) and boom I (20) are all connected in series by pilot passage (28). Pilot oil in pilot passage (28) goes through all of these valves and then goes through drain line (34) and back to the hydraulic tank.

Pilot passage (17) is open to swing parking brake control valve (1) through pilot line (10). Spool (2) in swing parking brake control valve (1) cannot be shifted because of low pressure in pilot passage (10). Oil in passage (4) goes through pressure reducing valve (3) which directs the oil through drain line (12). Swing parking brake (5) remains engaged.

Off Position

Activation of any controls other than travel closes pilot passage (28) and increases the pilot oil pressure in pilot passage (28). The oil pressure in pilot passage (17) and pilot line (10) also increases, causing spool (2) to shift. The oil now flows from line (30) through passage (4) to swing parking brake (5), releasing the swing parking brake.

Activation of travel control does not close pilot passage (28). The parking brake remains engaged.

Because pilot passage (28) is closed prior to the opening of swing control valve (25), the swing motor operates only after swing parking brake (5) has been released by the pilot pressure oil from line (30).

When swing and implements controls are in NEUTRAL position, pilot passage (28) is open to drain line (34), allowing the pilot oil pressure in pilot passage (17) and pilot line (10) to decrease. Spool (2) returns to the NEUTRAL position by its return spring. Now there is no pilot oil flow from line (30) to swing parking brake (5). The oil in swing parking brake (5) flows through swing parking brake control valve (1) through passage (4) and pressure reducing valve (3), and returns to hydraulic tank (39) through drain line (12). Swing parking brake (5) begins to be applied. Because the oil flow from passage (4) is restricted at pressure reducing valve (3), a delayed application of swing brake (5) results. Swing brake (5) remains released until the swing motor comes to a stop.

Swing Left Operation

For swing left operation, pilot oil is supplied through line (29) to swing control valve (25). The stem in swing valve (25) shifts (moves) up. The lower pump oil in parallel feeder passage (16) goes through passages (26) and (22), line (8) and enters swing motor rotary group (6). For swing left operation, the supply and return ports are reverse of swing right operation. This causes the upper structure to swing to the left.

NOTE: For information on operation of the swing parking brake, see the section, "Swing Motor".

Swing Motor

Swing Motor
(1) Relief valve. (2) Relief valve. (3) Motor head. (4) Port (parking brake pilot). (5) Swing parking brake control valve. (6) Port. (7) Plate. (8) Friction plate. (9) Body. (10) Shoe. (11) Plate. (12) Drain port. (13) Check valve. (14) Makeup port. (15) Passage. (16) Check valve. (17) Passage. (18) Port. (19) Passage. (20) Port. (21) Anti-reaction valve. (22) Valve plate. (23) Passage. (24) Brake spring. (25) Brake piston. (26) Piston. (27) Cylinder barrel. (28) Plate. (29) Drive shaft.

Introduction

The swing motor may be divided into the following four groups;

1. Rotary group: consisting of cylinder barrel (27), pistons (26), shoes (10), plate (11) and drive shaft (29).

2. Parking brake group: consisting of swing parking brake control valve (5), plates (7), friction plates (8), brake piston (25) and brake springs (24).

3. Relief and makeup valve group: consisting of relief valves (1) and (2), and check valves (13) and (16).

4. Anti-reaction valve (21) group.

Operation

The oil from the lower pump passes through the swing control valve. The swing control valve directs oil to port (18) or (20).

For a Swing Right operation, pump oil enters port (20) and goes through passage (19) in motor head (3), passage (15) in valve plate (22) and through passage (23) in cylinder barrel (27).

Pump oil in cylinder barrel (27) acts against piston (26). The piston forces shoe (10) against plate (28). The piston and shoe slide along the inclined surface of plate (28) from the top dead center to bottom dead center.

Motor Passages (Viewed From Head Side)
(15) Passage (in plate). (17) Passage. (18) Port. (19) Passage. (20) Port. (23) Passage (in cylinder barrel). (30) Passage (in plate). (31) Counterclockwise turn.

The force created by the shoe and the piston against plate (28) causes cylinder barrel (27) to rotate counterclockwise. Passage (23) of each piston that has come to the bottom dead center position is open to passage (30) in valve plate (22). Oil now returns to the hydraulic tank. The piston and the shoe continue to move up on the inclined surface of plate (28) as cylinder barrel (27) continues to turn counterclockwise.

For a Swing Left operation, pump oil is supplied to port (18). The supply and return ports are reversed. Cylinder barrel (27) and drive shaft (29) turn clockwise.

The case drain oil returns through drain port (12) of motor head (3) to the hydraulic tank.

Swing Parking Brake

Parking Brake (Partial)
(1) Spool. (2) Port. (3) Port. (4) Swing parking brake control valve. (5) Spool. (6) Passage. (7) Spring. (8) Passage. (9) Motor head. (10) Brake spring. (11) Piston chamber. (12) Brake piston. (13) Plate. (14) Friction plate. (15) Cylinder barrel. (16) Piston. (17) Body.

The swing parking brake group is located between motor head (9) and body (17). It is made up of brake springs (10), brake piston (12), plates (13), friction plates (14) and swing parking brake control valve (4).

Teeth on the inner circumference of friction plate (14) engage with splines on cylinder barrel (15). Teeth on the outer circumference of plates (13) engage with splines on the inner circumference of body (17).

Swing Parking Brake Control Valve (Brake Off Position)
(1) Spool. (2) Port. (3) Port. (4) Swing parking brake control valve. (5) Spool. (6) Passage. (7) Spring. (8) Passage. (18) Passage. (19) Passage. (20) Passage. (21) Passage.

When the swing control is activated, lower pump oil is supplied to the swing motor. Before supplied to the motor, the oil pressure through port (3) in swing parking brake control valve (4) increases and moves spool (1) down against the force of spring (7). This opens passages (18) and (19) allowing pilot oil pressure from port (2) to flow through passages (18) (19), (20) and (8) to piston chamber (11). The pilot oil pressure overcomes the force of brake springs (10) and moves brake piston (12) to the left. When the force that holds plates (13) and plates (14) together is released, the upper structure is then released for swing operation.

Swing Parking Brake Control Valve (Brake On Position)
(1) Spool. (2) Port. (3) Port. (4) Swing parking brake control valve. (5) Spool. (6) Passage. (7) Spring. (8) Passage. (18) Passage. (19) Passage. (21) Passage. (22) Filter. (23) Orifice. (24) Passage. (25) Spring chamber. (26) Spring.

When no pump oil is supplied to the swing motor, the pilot oil pressure through port (3) decreases. Spool (1) is pushed up by the force of spring (7), closing passage (18) and (19). Pilot oil flow is now blocked from port (2) to passage (8) and piston chamber (11). Brake piston (12) starts moving to the right by the force of brake springs (10). As brake piston (12) moves, the oil in piston chamber (11) goes through passage (8) to spool (5). The oil flow is restricted at orifice (23) causing an increase in oil pressure. The increased pressure oil moves spool (5) down against the force of spring (26) and decreases the opening of passage (24). The oil flow is restricted at orifice (23) and passage (24). Oil flows slowly through spring chamber (25) and passage (21) to the motor case drain. The force of brake springs (10) holds brake piston (12) together with plates (13) and friction plates (14) to body (17). The upper structure is now locked to the lower structure, preventing rotation of the upper structure.

The restricted oil flow delays application of the parking brake. If the oil flow was not restricted at orifice (23) and passage (24), the parking brake would start to apply before a machine swing operation stops.

Relief/Makeup Operation

Swing Circuit Schematic (Partial)
(1) Passage. (2) Makeup port. (3) Relief valve. (4) Passage. (5) Motor rotary group. (6) Swing motor. (7) Passage. (8) Relief valve. (9) Passage. (10) Makeup line. (11) Check valve. (12) Port. (13) Port. (14) Check valve. (15) Check valve. (16) Return line. (17) Main control valves. (18) Slow return check valve. (19) Return line.

Swing Motor Compartment
(2) Makeup port. (3) Relief valve. (6) Swing motor. (8) Relief valve. (10) Makeup line.

Relief Valve

Relief Valve
(1) Passage. (4) Passage. (20) Spring. (21) Passage. (22) Piston. (23) Body. (24) Stem. (25) Passage. (26) Plug. (27) Spring chamber. (28) Orifice. (29) Sleeve. (30) Piston chamber. (31) Piston. (32) Plug. (33) Spring. (34) Orifice.

Relief valves (3) and (8) are located in the top of swing motor (6). These valves limit the pressure in the swing circuit to the relief setting. This provides a cushion effect at a start or stop of the swing operation.

When there is not enough oil supplied to swing motor (6) (at a stop of the swing operation), part of the return oil from main control valves (17) is sent to the motor as makeup oil. This removes the vacuum condition.

When the swing control lever is moved back to NEUTRAL position, during Swing Right operation, inlet and outlet ports of the swing control valve are closed. Oil flow is now blocked at port (12) and port (13) of the swing motor.

The mass (weight and size) of the upper structure causes the swing motor to rotate after a stop operation is made. The continued operation attempts to draw oil from port (13) and force it out port (12). Since port (12) is closed, the pressure of the blocked oil in passage (1) increases. The increased pressure oil in passage (1) forces stem (24) to open against the force of spring (33) in relief valve (3). Oil now flows through passage (4) and check valve (14) to passage (7). From passage (7), oil enters motor rotary group (5). The force of the rotating upper structure is now absorbed as the swing motor comes to a stop.

The oil in passage (1) goes through orifice (34) of stem (24) to piston chamber (30). Because the force of spring (33) is less than the relief valve pressure setting [27 500 kPa (4000 psi)], stem (24) opens just before the pressure in passage (1) reaches the relief setting. This allows the oil to vent. The pressure oil in piston chamber (30) moves piston (22) to the left, compressing spring (20) until its left end face comes in contacts with plug (26). The oil in spring chamber (27) goes through orifice (28) of sleeve (29), passages (21) and (25) to passage (4). In approximately 0.1 second of piston movement, the pressure oil in piston chamber (30) increases, moving piston (31) to the right by compressing spring (33). When piston (31) comes in contact with the shoulder of plug (32), the oil pressure in passage (1) increases to the relief setting [27 500 kPa (4000 psi)]. It is not until the full relief pressure setting is reached that all of the oil is allowed to flow out of relief valve (3) to passage (4).

Because of the two stage relief action, no peak pressure builds up when relief valve (3) opens. Less shock load occurs when the swing motor stops.

At the start of a swing right operation, there is a pressure increase in oil supplied to port (13) because of the mass (weight and size) of the upper structure. Part of the pressure oil flows past stem (24) in relief valve (8) and through makeup port (2) to return line (19). This gives a smoother acceleration at the start of a swing operation.

Oil Makeup

As previously described, when rotation of the swing motor is stopped, all ports in the swing control valve are blocked. There is no pump oil sent to swing motor (6). As the upper structure attempts to continue rotating, part of the oil in swing motor (6) is lost in the form of internal leakage. Because of this oil loss, a vacuum occurs at port (13). To prevent this vacuum condition, oil from return line (16) goes through makeup line (10), makeup port (2), passage (9), check valve (14) and passage (7) into motor rotary group (5).

Slow Return Check Valve

Main Control Valve Compartment
(10) Makeup line. (18) Slow return check valve. (19) Return line.

Slow Return Check Valve
(10) Makeup line. (16) Return line. (18) Slow return check valve (19) Return line.

Slow return check valve (18) is located downstream of return line (16). Slow return check valve (18) makes it possible to makeup lost oil during a swing stop operation.

When all of main control valves (17) are in Neutral position, the oil from the upper and lower pumps goes through line (16) to the hydraulic tank. Check valve (15) causes a resistance to the oil flow in return line (16) maintaining the oil pressure at 290 kPa (43 psi).

When there is not enough oil supplied to the swing motor, this return line back pressure adds oil flow to the motor rotary group through makeup port (2) and passage (9).

When the swing motor speed is decreased during a high speed right swing, by moving the swing control lever partially to NEUTRAL position, oil supply from port (13) decreases. Since the swing control valve is partially open, the oil flow now continues to flow through port (12) to return line (16). On port (12) side, the pressure is lower than the setting of relief valve (3). Relief valve (3) is kept closed and there is no makeup oil sent to passage (7) through check valve (14). A vacuum now develops at port (13) side. Check valve (14) causes makeup oil flow from makeup line (10) to motor rotary group (5), eliminating the vacuum condition.

If the swing motor is stopped or decelerated during a swing operation in the opposite direction and oil is supplied through port (12), check valve (11) instead of check valve (14) operates to prevent vacuum in the swing motor.

Anti-Reaction Valve

Anti-Reaction Valve (Neutral Position)
(1) Passage. (2) Swing motor rotary group. (3) Passage. (4) Valve. (5) Spring. (6) Spring. (7) Anti-reaction valve. (8) Passage. (9) Motor head. (10) Spring. (11) Passage. (12) Passage. (13) Valve. (14) Passage. (15) Passage. (16) Passage. (17) Piston chamber. (18) Piston. (19) Passage. (20) Valve chamber.

At a stop of swing operation, it is difficult to smoothly stop the upper structure and implements at a desired position due to the mass (weight and size) of the upper structure. This is because the pressure of the blocked oil in the swing motor outlet side goes back to the swing motor rotary group, causing the upper structure to swing in the reverse direction. Anti-reaction valve (7) prevents the blocked oil from flowing back to the swing motor rotary group. Anti-reaction valve (7) is located in the-motor head (9) of the swing motor.

Swing motor rotary group (2) gets pump oil from passage (1) or (3) in motor head (9). Anti-reaction valve (7) is open to both passages (1) and (3). Oil in passage (1) goes through passages (8), (11) and (16) to piston chamber (17). Oil in passage (3) goes through passages (12), (14), (15) and (19) to valve chamber (20).

When there is no oil pressure in both passages (1) and (3), valve (4) is moved to the right by the force of springs (5) and (6) until stopped by piston (18). Valve (13) is moved to the right by the force of spring (10) until its right end shoulder comes in contact with valve (4).

When swing motor rotary group (2) gets pump oil from passage (3), it rotates counterclockwise. When pump oil from passage (3) is blocked, motor rotary group (2) continues to rotate counterclockwise because of the mass (weight and size) of the upper structure. The oil pressure blocked in passage (1) increases and the oil pressure in passage (3) decreases. The increased pressure oil in passage (1) goes through passages (8), (11) and (16), into piston chamber (17). The oil pressure in piston chamber (17) moves valve (4) to the left against the forces of springs (5) and (6). Valve (13) is shifted to the left compressing spring (10).

Anti-Reaction Valve (During Activation)
(1) Passage. (2) Swing motor rotary group. (3) Passage. (4) Valve. (5) Spring. (6) Spring. (8) Passage. (10) Spring. (11) Passage. (13) Valve. (16) Passage. (17) Piston chamber.

When swing motor rotary group (2) gets pump oil from passage (3), it rotates counterclockwise. When there is no oil supplied to passage (3), swing motor rotary group (2) continues to rotate counterclockwise because of the mass (weight and size) of the upper structure. The oil pressure blocked in passage (1) increases and the oil pressure in passage (3) decreases. The increased oil pressure in passage (1) goes through passages (8), (11) and (16), and enters piston chamber (17). The pressure oil in piston chamber (17) moves valve (4) and valve (13) to the left against the combined force of springs (5), (6) and (10).

Anti-Reaction Valve (Just Before The Motor Stops)
(1) Passage. (2) Swing motor rotary group. (3) Passage. (4) Valve. (5) Spring. (6) Spring. (10) Spring. (12) Passage. (13) Valve. (14) Passage. (17) Piston chamber. (21) Valve chamber. (22) Orifice. (23) Passage. (24) Passage.

As the motor attempts to stop due to decreased force of the mass (weight and size) of the upper structure, the oil pressure in passage (1) decreases. Now the oil pressure in piston chamber (17) is less than the combined force of springs (5) and (6), valve (4) moves to the right. Valve (13) slowly moves to the right because the force of spring (10). Because the oil flow from valve chamber (21) is restricted at orifice (22). Now valves (13) and (14) separates from each other. Passage (24) opens allowing oil flow from passage (1) through passages (24), (23), (14) and (12) to passage (3). When the pressure oil in passages (1) and (3) becomes the same, valve (13) stops closing passage (24). Now there is no oil going back from passage (1) to swing motor rotary group (2). The upper structure and each implement can stop smoothly at a desired position.

When swing motor rotary group (2) gets pump oil from passage (1), the oil pressure in passage (3) increases at the stop of a swing operation. The increased oil pressure blocked in passage (3) goes through passages (12), (14), (15) and (19), and into valve chamber (20). The pressure oil in valve chamber (20) moves valves (4) and (13) to the left against the combined force of springs (5), (6) and (10).

As the oil pressure in chamber (20) decreases, valve (4) moves to the right and then valve (13) slowly moves to the right.

In the same manner as described before, valves (4) and (13) separate from each other opening passage (24). Now there is no oil going back from the swing motor outlet port to the swing motor rotary group.

Swing Drive

Swing Drive
(1) First stage carrier. (2) First stage planet gear. (3) Second stage carrier. (4) Ring gear. (5) Second stage planet gear. (6) Roller bearing. (7) Roller bearing. (8) Pinion shaft. (9) Swing motor. (10) Shaft (swing motor). (11) First stage sun gear. (12) Second stage sun gear. (13) Coupling. (14) Housing. (15) Bearing gear (swing bearing).

The swing drive consists of a series of planet gears. The planet gears reduce the rotating speed of swing motor (9). The swing motor is bolted on the swing drive. The swing drive is bolted to the upper structure. The teeth of the swing drive output pinion shaft (8) engage with bearing gear (15) of the swing bearing. Pinion shaft (8) provides motion to the upper structure by rotating around bearing gear (15). Bearing gear (15) is attached to the lower structure.

The swing drive is divided into the following two groups:

1. The first group functions as a double reduction of motor speed. The first stage reduction consists of first stage sun gear (11), first stage planet gears (2), first stage carrier (1) and ring gear (4). The second stage reduction consists of second stage sun gear (12), second stage planet gears (5), second stage carrier (3) and ring gear (4).

2. The second group functions as the drive for reduced motor speed output. It consists of coupling (13) and pinion shaft (8). Piston shaft (8) is supported by roller bearings (6) and (7) located in housing (14).

The planet reduction group functions to reduce the swing speed in a ratio of sun gear tooth numbers to ring gear tooth numbers. The compact swing drive with the sun gear incorporated in the ring gear housing provides a greater reduction ratio.

First Stage Planetary Gear Rotation
(1) First stage carrier. (2) First stage planet gear. (4) Ring gear. (11) First stage sun gear. (16) Shaft (first stage planet gear).

Swing motor output shaft (10) is splined to first stage sun gear (11). First stage planet gears (2) of first stage carrier (1) are in mesh with first stage sun gear (11). As shaft (10) rotates first stage sun gear (11) counterclockwise, first stage planet gears (2) rotate clockwise on shafts (16), moving counterclockwise around ring gear (4). Ring gear (4) is bolted to housing (14). First stage carrier (1) now rotates counterclockwise.

Swing Drive (Partial)
(1) First stage carrier. (2) First stage planet gear. (3) Second stage carrier. (4) Ring gear. (5) Second stage planet gear. (6) Roller bearing. (7) Roller bearing. (8) Pinion shaft. (11) First stage sun gear. (12) Second stage sun gear. (13) Coupling. (17) Inner circumference.

Splines on inner circumference (17) of first stage carrier (1) engage with the splines on second stage gear (12). This causes second stage sun gear (12) to rotate counterclockwise. Second stage planet gears (5) now turn clockwise on their shafts, moving counterclockwise around ring gear (4) in the same manner as in the first stage. Second stage carrier (3) and coupling (13) are splined to each other. The splines of pinion shaft (8) engage with splines on the inner circumference of coupling (13), causing pinion shaft (8) to rotate counterclockwise.

Pinion Shaft (8) Rotation
(8) Pinion shaft. (15) Bearing gear (swing bearing). (18) Location of moving pinion shaft.

Pinion shaft (8) engages with bearing gear (15) on the inner circumference of the swing bearing. As pinion shaft (8) rotates counterclockwise, it moves clockwise around bearing gear (15). Bearing gear (15) is bolted to the lower structure. This causes the upper structure to swing to the right (clockwise).

Hydraulic Schematic For Fine Swing Control

(1) Swing parking brake control valve. (2) Spool. (3) Line. (4) Swing parking brake. (5) Motor rotary group. (6) Pilot line. (7) Passage. (8) Swing motor. (9) Passage. (10) Fine swing solenoid valve. (11) Orifice. (12) Passage. (13) Passage. (14) Line. (15) Line. (16) Pilot line. (17) Return passage. (18) Line. (19) Swing control valve. (20) Lower pump. (21) Pilot pump. (22) Hydraulic tank.

Fine Swing Control

Introduction

When the control lever is returned to the NEUTRAL position from swing operation position, an increase in oil pressure occurs at the drain port of the swing motor due to the mass (weight and size) of the upper structure. This prevents the upper structure from smoothly stopping at an exact position. The fine swing control system functions for the upper structure to stop with a minimal shock load by slowing down its swing movement at an optimum rate. The fine swing control is suitable for applications such as pipe laying or placement of timbers, which need an exact fine swing movement.

Operation

Swing Motor Compartment
(1) Swing parking brake control valve. (3) Line. (6) Pilot line. (8) Swing motor. (10) Fine swing solenoid valve. (14) Line. (15) Line. (16) Pilot line. (18) Line. (23) Block.

Left Console
(24) Fine swing control switch.

The major components that make up the fine swing control system are fine swing solenoid valve (10) and fine swing control switch (24). Fine swing solenoid valve (10) is located on the top of swing motor (8). Fine swing control switch (24) is located on the left console. When fine swing control switch (24) is turned on, fine swing solenoid valve (10) activates (energizes).

When the control lever is moved to the RIGHT SWING position, lower pump oil goes through swing control valve (19), line (14) and passage (9) to motor rotary group (5) in swing motor (8). The oil then goes through passage (7), line (15) and swing control valve (19), and returns to hydraulic tank (22) through return passage (17). When fine swing control switch (24) is in the OFF position, pilot oil in pilot line (16) goes through fine swing solenoid valve (10) and pilot line (6) to spool (2) in swing parking brake control valve (1).

At the same time, pilot oil from pilot pump (21) goes through line (3) to spool (2) in swing parking brake control valve (1). When the swing control is activated, oil pressure in passage (16) increases, shifting spool (2) to its open position. This allows the pilot oil from line (3) to go through spool (2) to swing parking brake (4). Now the swing parking brake releases.

When fine swing control switch (24) is in the OFF position [fine swing solenoid (10) is deenergized], there is no open connection between passages (7) and (9) through fine swing solenoid valve (10) and orifice (11).

When the swing control lever is returned to the NEUTRAL position from the RIGHT SWING position with fine swing control switch (24) in ON position, the fine swing control system activates as follows;

1. Swing control valve (19) closes, but motor rotary group (5) continues to rotate by the mass (weight and size) of the upper structure. Oil pressure in passage (7) increases and oil pressure in passage (9) decreases.

2. Fine swing solenoid valve (10) is energized, causing the following oil flows;

a. Passage (7) is open to passage (9) through passage (13), orifice (11) and passage (12).

b. Pilot oil from pilot line (16) is blocked at fine swing solenoid valve (10).

c. Pilot oil from pilot pump (21) goes through line (18) and pilot line (6) to swing parking brake (4). The swing parking brake is released.

3. The increased pressure oil in passage (7) goes through passage (13), orifice (11), passages (12) and (9) to motor rotary group (5). Because passage (7) is open to the low pressure side through orifice (11), the pressure of the oil to motor rotary group (5) decreases. This slows down the speed of motor rotary group (5) at a controlled rate.

4. When the swing control lever is partially moved to the opposite (left swing) position from the NEUTRAL position, swing action will stop at this position due to the slower flow rate. When the swing control lever is again returned to the NEUTRAL position from the partially moved position immediately after the swing stop, no shock load occurs because passages (7) and (9) are connected. Now the upper structure comes to a complete stop with no shock at the desired position.

NOTE: Turning fine switch control switch (24) off, instead of partially moving the swing control lever in the opposite direction, will allow a complete stop of the upper structure with minimal shock load.

The fine swing control system in a Left Swing operates in the same manner as that described for Right Swing except the oil pressure in passage (9) increases and the oil pressure in passage (7) decreases.

NOTE: When parking a machine on a slope, be sure that the fine swing control switch is turned Off and the bucket is securely lowered to the ground.

Fine Swing Solenoid Valve

Fine Swing Solenoid Valve(Deenergized Position)
(2) Spool. (3) Line. (4) Swing parking brake. (5) Motor rotary group. (6) Pilot line. (7) Passage. (9) Passage. (10) Fine swing solenoid valve. (11) Orifice. (12) Passage. (13) Passage. (14) Line. (15) Line. (16) Pilot line. (18) Line. (23) Block. (25) Passage. (26) Spool. (27) Spring.

Fine Swing Solenoid Valve In Deenergized Position;

When fine swing control switch (24) is in the Off position, fine swing solenoid valve (10) is deenergized. Spool (26) in fine swing solenoid valve (10) is shifted to the right by the force of spring (27). Under this condition, the following oil flows occur within fine swing solenoid valve (10).

1. Spool (26) blocks oil flows from line (18) to passages (13) and (25).

2. Pilot lines (16) and (6) are connected.

When the control lever is moved to the RIGHT SWING position, lower pump oil and pilot pump oil flow as follows;

1. Lower pump oil from line (14) enters block (23) attached to swing motor (8). The lower pump oil then goes through passage (9), motor rotary group (5) and passage (7) to line (15), rotating motor rotary group (5).

2. Pressure oil in pilot line (16) goes through line (6) to spool (2), shifting spool (2) to its open position. Oil from pilot pump (21) goes through line (3) and spool (2) to swing parking brake (4). The swing parking brake is released.

Swing motor (8) normally operates regardless of the functions of fine swing solenoid valve (10).

Fine Swing Solenoid Valve In Energized Position

When fine swing control switch (24) is turned ON at the same time the swing control lever is returned to the NEUTRAL position from the RIGHT SWING position, fine swing solenoid valve (10) is energized. Spool (26) shifts to the left against the force of spring (27). Under this condition, following oil flows occur within fine swing solenoid valve (10).

1. Passages (25) and (13) are connected.

2. Line (18) and pilot line (6) are connected.

3. Pilot line (16) is blocked at spool (26).

Now lower pump oil and pilot pump oil flow as follows;

1. When the swing control lever is returned to the NEUTRAL position, motor rotary group (5) is still in rotation by the mass (weight and size) of the uppers structure. Because both oil flows from lines (14) and (15) are blocked at swing control valve (19), drain oil from motor rotary group (5) goes through passages (7), (13) and (25), orifice (11), passages (12) and (9), to the inlet port of motor rotary group (5). Because orifice (11) decreases the oil pressure in passage (7), motor rotary group (5) decreases its speed at a controlled rate.

2. Pilot pump oil from line (18) goes through pilot line (6) to spool (2). Spool (2) is shifted, allowing an oil flow from line (3) to swing parking brake (4). The swing parking brake is now released.

Because the inlet and outlet ports of motor rotary group (5) are connected with the swing parking brake disengaged, swing movement slows down at an optimum rate. When the swing control lever is partially moved to the REVERSE (swing left) position, the upper structure stops at this point. When the swing control lever is again returned to the NEUTRAL position from the partially moved position immediately after the stop, no shock load occurs at motor rotary group (5) because connected passages (7) and (8) equalize oil pressure at both inlet and outlet ports of rotary group (5). Now the upper structure stops at an exact, desired point with a minimal shock load.

Hydraulic Schematic For Forward Travel

(1) Left travel motor.

(2) Swashplate.

(3) Motor rotary group.

(4) Piston.

(5) Passage.

(6) Passage.

(7) Displacement change valve.

(8) Counterbalance valve.

(9) Passage.

(10) Parking brake.

(11) Piston.

(12) Passage.

(13) Passage.

(14) Line.

(15) Right travel motor.

(16) Swashplate.

(17) Passage.

(18) Piston.

(19) Passage.

(20) Passage.

(21) Passage.

(22) Piston.

(23) Passage.

(24) Passage.

(25) Displacement change valve.

(26) Passage.

(27) Line.

(28) Line.

(29) Line.

(30) Line.

(31) Swivel.

(32) Line.

(33) Line.

(34) Passage.

(35) Passage.

(36) Return passage.

(37) Return line.

(38) Left travel control valve.

(39) Passage.

(40) Center bypass passage.

(41) Right travel control valve.

(42) Pilot control valve (right/left travel).

(44) Solenoid valve (travel speed).

(45) Line.

(46) Line.

(47) Upper pump.

(48) Pilot pump.

(49) Shuttle valve.

(50) Lower pump.

(51) Line.

(52) Automatic travel speed change valve.

Travel Control

Introduction

Travel Motor
(1) Left travel motor. (53) Brake valve.

Travel Drive
(54) Left track. (55) Sprocket. (56) Left travel drive.

Left travel motor (1) and right travel motor (15) are supplied pump oil through swivel (31) from lower pump (50) and upper pump (47). When left travel motor (1) is operated by lower pump oil, the motor torque is transmitted to left travel drive (56). Left travel drive (56) reduces the speed and increases the torque of left travel motor (1). The increased torque turns left track (54). Left track (54) is connected to left travel drive (56) through sprocket (55).

Console
(57) Travel speed switch.

Travel speed switch (57) provides a selection of HIGH or LOW travel speed. During partial movements of the travel control lever, the travel speed varies with the travel distance of the lever. When the switch is placed in the SLOW "TORTOISE" position, the machine travels at the LOW speed mode. When the switch is placed in the FAST "RABBIT" position, the machine travels at the HIGH speed mode. On a flat surface or moderate downward slope, select the HIGH speed for increased mobility.

While travel speed switch (57) is in HIGH TRAVEL SPEED MODE position, automatic travel speed change valve (52) operates to automatically change the travel speed depending on the load placed on the machine. The machine travels at LOW speed when a larger load is placed on it and travels at HIGH speed when a smaller load is placed.

Illustration Of Travel Operation
(1) Left travel motor. (15) Right travel motor. (58) Forward direction. (59) Control lever/pedal (left travel). (60) Idler location. (61) Control lever/pedal (right travel). (62) Cab. (63) Reverse direction.

The direction of travel (forward or reverse) is relative to the position of the lower structure. For normal travel, idler location (60) is positioned in front of cab (62) and travel motors (1) and (15) to the rear of the cab. With the machine in the normal position of travel, move the control levers/pedals (59) and (61) forward. The machine will travel in forward direction (58). This movement is called forward travel. When levers/pedals (59) and (61) are moved to the rear, the machine travels in reverse direction (63). This direction is called reverse travel.

When cab (62) is turned 180i, travel motors (1) and (15) will be positioned in front of the cab. The direction of travel and operation of levers/pedals (59) and (61) are reverse to when the machine is in the normal travel direction.

A pivot turn is made when the traveling direction of the machine is to be changed. When only one of levers/pedals (59) or (61) is moved forward, the respective track travels forward. Since the opposite track is stationary, the machine turns with the stationary track as its axis (pivot point). This is called a pivot turn.

A spot turn is made when the traveling direction of the machine is to be changed in a narrow place. To complete a spot turn operation, move one control lever/pedal to the rear and the other control lever/pedal forward at the same time. The tracks will travel in the opposite direction of each other. The machine makes a minimum radius (spot) turn with its center as its axis.

Forward Travel Operation

Main Control Valve Compartment
(38) Left travel control valve. (41) Right travel control valve.

When travel control levers are operated, pilot oil from pilot control valve (42) shifts the stems in travel control valves (38) and (41). Travel control valves (38) and (41) allow oil flow from lower pump (50) and upper pump (47) to swivel (31). The swivel transfers oil from the rotating upper structure to the lines in the lower structure. The oil flows to left and right travel motors (1) and (15).

NOTE: Since right and left travel controls function the same, explanations are given relative to left travel control.

The pilot oil from pilot valve (42) goes through line (27) and enters left travel control valve (38). The pilot oil shifts the stem in left travel control valve (38), allowing the lower pump oil in center bypass passage (40) to go through passage (39) to passage (35). The pilot oil now goes through line (33), swivel (31), line (29) and counterbalance valve (8), and enters motor rotary group (3) through passage (11).

Now part of the lower pump oil flows through counterbalance valve (8) and passage (7) to parking brake (10). Parking brake (10) releases, causing the left travel motor to rotate in the forward direction.

Low Speed

When travel speed switch (57) is placed in the LOW SPEED MODE position, part of the pilot oil in passage (11) goes through passage (13) and displacement change valve (12) to piston (9). Piston (9) turns cam plate (2) in the increased angle direction and holds it at its maximum angle (large displacement) position. Now more oil is required to turn left travel motor (1), causing the motor to rotate at a lower speed. The left track travels at a lower speed and increases its drawbar pull.

Return oil from motor rotary group (3) flows through passage (5), counterbalance valve (8) and line (30) to swivel (31). Oil now goes through line (32) and passage (34) into left travel control valve (38). The oil leaves left travel control valve (38) and goes through return passage (36) and back to the hydraulic tank through return line (37).

Oil from the upper pump turns right travel motor (15). Operation of right travel is the same as that described for left travel.

High Speed

Pilot Oil Manifold Compartment
(44) Solenoid valve (travel speed).

The explanation for forward travel in the HIGH SPEED MODE position is given relative to right travel motor (15). Operation is the same for left travel motor (1).

When travel speed switch (57) is placed in the HIGH SPEED MODE position, travel speed solenoid valve (44) is energized. If the pump delivery pressure does not increase to a certain level due to smaller machine load, automatic travel speed change valve (52) remains open. Oil from pilot pump (48) flows through travel speed solenoid valve (44), line (45), automatic travel speed change valve (52), line (46), swivel (31) and line (14) to displacement change valve (25). The spool in displacement change valve (25) shifts. As the spool shifts, oil from the upper pump flows through passages (26), displacement change valve (25) and passage (23) to piston (22). Now the oil that is pushed by piston (18) goes through passage (19), displacement change valve (25) and passage (24) to the motor case drain.

The pressure oil in passage (23) pushes piston (22), decreasing the angle of swashplate (16) and holds it in its minimum angle position. Less oil is now required to turn right travel motor (15). The motor turns at a higher speed.

Automatic Travel Speed Change Valve

Part of oil from upper (47) and lower (50) pumps combines at shuttle valve (49). The combined oil flow now goes through line (51) to automatic travel speed change valve (52). With travel speed switch (57) in HIGH TRAVEL SPEED position, the travel motor runs at a smaller angle position of its swashplate until the machine load increases to a certain level. The pump delivery pressure increases as the load placed on the machine increases. As the delivery pressure increases to a certain level, the oil pressure from line (51) shifts automatic speed change valve (52) to close the connection of lines (45) and (46). Now there is no pilot oil supplied to displacement change valve (25). Displacement change valve (25) is shifted to off position, causing the swashplate of the travel motor to turn in the increased angle for the low speed. The machine travels at the low speed.

If the machine load is decreased, the pump delivery pressure is decreased. as the circuit pressure in line (51) decreases to an certain range, automatic speed change valve (52) opens again, connecting lines (45) and (46). Displacement change valve (25) is now supplied pilot oil from line (45) and re-activates to turn the motor swashplate at a smaller angle for high speed mode. Now, the machine again travels at the high speed.

Automatic speed change valve (52) functions so the machine travels at the high speed when a smaller load is placed, and at the low speed when a larger load is placed. This assures a higher mobility and drawbar pull.

NOTE: If the hydraulic oil temperature is below 25°C, the travel speed remains low even with travel speed switch (57) in HIGH SPEED (rabbit) position.

Pilot Control Valve (Travel)

Pilot Control Valve (Travel)
(1) Control lever/pedal. (2) Pedal. (3) Rod. (4) Seat. (5) Spring. (6) Spring. (7) Spool. (8) Passage. (9) Passage. (10) Spring. (11) Spool. (12) Return port. (13) Return chamber. (14) Passage. (15) Passage. (16) Pilot port. (17) Passage. (18) Port. (19) Passage. (20) Passage. (21) Passage. (22) Port.

When control lever/pedal (1) is moved to the FORWARD TRAVEL position, pedal (2) pushes down on rod (3) and seat (4) against the force of springs (5) and (6). Spool (7) moves down and opens passage (19) by compressing spring (6).

As passage (19) is opened, the oil from pilot port (16) goes through passages (21), (19), (20), (9), and out port (18) to the travel control valve. The pressure oil on the end of the travel control valve stem causes the travel control valve stem to move into the forward position.

The oil from the chamber at the opposite end of the main control valve for travel comes back through port (22), through passage (17), (15) and (14). The oil now flows into return chamber (13) and back to the hydraulic tank through return port (12).

When lever/pedal (1) is partially moved for fine travel operation, rod (3) moves down with seat (4) causing spring (6) to push spool (7) down. Passage (19) opens and the pressure oil increases at port (18). Since the oil pressure is more than the force of spring (6), spool (7) moves up opening passage (8). The oil from port (18) goes through passages (9), (20) and (8) into return chamber (13). The oil pressure slightly decreases. Spool (7) is now held in a pressure modulating position and establishes a balance between the pressure in port (18) and the force of spring (6).

NOTE: For details of how the pressure at port (18) varies, see "Pilot Control Valve For Implements And Swing" in the section, "Pilot Circuit".

When the control lever/pedal is released, spring (5) pushes up on seat (4) and rod (3). The pedal returns the lever to the NEUTRAL position. Spool (7) moves up. The oil in port (18) can now flow through passage (9), (20), (8) and return chamber (13) and back to the hydraulic tank.

When control lever/pedal (1) is moved to the REVERSE TRAVEL position, operation is the same as that described for FORWARD TRAVEL position.

Travel Motor

Travel Motor
(1) Shaft. (2) Shoe. (3) Plate. (4) bushing. (5) Spacer. (6) Piston. (7) Cylinder. (8) Pin. (9) Separator plate. (10) Friction plate. (11) Brake piston. (12) Brake spring. (13) Head. (14) Passage. (15) Stopper. (16) Piston. (17) Swashplate. (18) Piston. (19) Stopper. (20) Cylinder spring. (21) Rod. (22) Spring. (23) Passage. (24) Passage. (25) Spool. (26) Valve plate. (27) Plug. (28) Displacement change valve. (29) Crossover relief valve. (30) Drain port. (31) Port (automatic speed change). (32) Port. (33) Port. (34) Crossover relief valve. (35) Counterbalance valve. (36) Pressure releasing valve. (37) Check valve. (38) Check valve.

The travel motor can be divided into the following four groups.

1. Rotary group: consisting of shaft (1), bushing (4), spacer (5), cylinder spring (20), cylinder (7), plate (3), shoes (2) and piston (6).

2. Brake valve group: consisting of counterbalance valve (35) and crossover relief valves (29) and (34).

3. Parking brake group: consisting of friction plates (10), separator plate (9), brake piston (11), brake springs (12), pins (8) and pressure releasing valve (36).

4. Displacement change group: consisting of displacement change valve (28), check valves (37) and (38), pistons (16) and (18), and rod (21).

Depending on travel direction, pump oil goes into the travel motor through port (32) or (33) and is forced out through port (33) or (32).

The case drain oil that has leaked from the sliding surfaces and clearances returns to the hydraulic tank through drain port (30) of head (13).

Pump supply oil from the lower pump goes in the left travel motor through port (33) during forward travel. The oil from port (33) goes through passage (14) in head (13) to passage (24) of valve plate (26). The pump oil now goes through passage (23) of cylinder (7) and forces piston (6) to the left.

Motor Passages [Viewed From Head (13) Side]
(23) Passage (cylinder). (24) Passage (valve plate). (39) Passage (valve plate).

Shoe (2) (coupled to the piston) slides on the surface of swashplate (17) from the top center to the bottom center, and rotates with cylinder (7). The pressure oil that is forced out by the pistons on the outlet side goes through passage (23) and passage (39) of valve plate (26) and out through port (32). The cylinder turns counterclockwise.

Shaft (1) is splined to the cylinder. The shaft and barrel rotate counterclockwise for forward travel.

In REVERSE TRAVEL position, port (33) functions as an oil return port and port (32) functions as a supply port. The left travel motor rotates clockwise.

As the right travel motor is supplied upper pump oil through port (33), the right travel motor turns counterclockwise for reverse travel. Pump oil through port (32) turns the motor clockwise for forward travel.

Parking Brake

Parking Brake (Partial)
(1) Body. (2) Pin. (3) Friction plate. (4) Separator plate. (5) Piston chamber. (6) Passage. (7) Orifice. (8) Brake piston. (9) Spring. (10) Cylinder. (11) Passage. (12) Shaft.

As pump oil is supplied to the travel motor, the parking brake is released and the motor starts rotation. When there is no pump oil supplied to the motor, it stops rotation and the parking brake mechanically engages.

In the parking brake section of the travel motor, friction plates (8) are splined to cylinder (10). Separator plates (4) are splined to body (1).

Travel Motor (Partial)
(1) Body. (3) Friction plate. (4) Separator plate. (5) Piston chamber. (8) Brake piston. (13) Passage. (14) Passage. (15) Orifice. (16) Spring chamber. (17) Spool. (18) Spring. (19) Passage. (20) Bushing. (21) Spring seat. (22) Plug. (23) Pressure releasing valve.

When no pump oil is supplied to the travel motor, brake piston (8) is pushed to the left by the force of spring (9). The oil in piston chamber (5) now goes through passage (13), and through orifice (15) into spring chamber (16) in pressure releasing valve (23). The oil flow is restricted at orifice (15), causing its pressure to increase. Spool (17) is shifted to the right against the force of spring (18), decreasing the opening of passage (19). The oil in spring chamber (16) goes through passage (14) to the motor case drain.

When brake piston (8) moves to the left, friction plates (3) and separator plates (4) are held together against body (1) by the force of spring (9). Spring (9) is working against brake piston (8). The rotation of cylinder (10) stops and shaft (12) engages the parking brake.

Orifice (15) restricts return oil flow from piston chamber (5). The restriction of return oil flow delays application of the parking brake. If the return oil was not restricted by orifice (15), the parking brake would start to apply before travel of the machine is stopped. This would result in earlier wear and/or damage.

Prior to the operation of the travel motor, a portion of the pressure oil goes to passage (11). The oil then flows through orifice (7) and passage (6) to piston chamber (5). Brake piston (8) moves to the right against the force of spring (9). The oil pressure holding plates (3) and (4) together is released allowing cylinder (10) and shaft (12) to turn.

Displacement Change Valve

Large Displacement Change Operation

Travel Motor (Partial)
(1) Swashplate. (2) Piston. (3) Displacement change valve. (4) Check valve. (5) Passage. (6) Piston. (7) Port (8) Passage. (9) Passage. (10) Check valve. (11) Port. (12) Port. (13) Spring. (14) Spool. (15) Plug.

Displacement Change Operation (Large Displacement)
(1) Swashplate. (2) Piston. (3) Displacement change valve. (4) Check valve. (5) Passage. (6) Piston. (7) Port. (9) Passage. (10) Check valve. (13) Spring. (14) Spool. (15) Plug. (16) Stopper. (17) Piston chamber. (18) Piston chamber. (19) Stopper. (20) Rod. (21) Passage. (22) Passage. (23) Passage. (24) Passage. (25) Passage. (26) Passage.

When the travel speed switch is placed in the LOW SPEED MODE position, the travel speed solenoid valve is not energized. There is no pilot oil supplied to port (7) of displacement change valve (3). The force of spring (13) moves spool (14) to the right until it comes in contact with plug (15). The pump oil from port (12) of the motor flows through passage (9), check valve (10), passages (26), (25) and (21) to piston chamber (17). Piston (6) moves to the right. Swashplate (1) rotates for its increased angle direction.

The oil in piston chamber (18) drains to the hydraulic tank through passages (22), (24) and (23).

The motor now holds the swashplate at its maximum angle position for large displacement.

Small Displacement Change Operation

Displacement Change Operation (Small Displacement)
(1) Swashplate. (2) Piston. (3) Displacement change valve. (4) Check valve. (5) Passage. (6) Piston. (7) Port. (9) Passage. (10) Check valve. (13) Spring. (14) Spool. (15) Plug. (16) Stopper. (17) Piston chamber. (18) Piston chamber. (19) Stopper. (21) Passage. (22) Passage. (23) Passage. (25) Passage. (26) Passage. (27) Passage. (28) Passage. (29) Passage.

When the travel speed switch is placed in the HIGH SPEED MODE position, the travel speed solenoid valve is energized. If the pump delivery pressure is below a certain level due to a smaller machine load, pilot oil flows to port (7) of displacement change valve (3). Pilot oil moves spool (14) to the left against the force of spring (13). Passage (25) closes and passage (28) opens.

Pump oil flows through passages (26), (28) and (22) to piston chamber (18), moving piston (2) to the left. Swashplate (1) turns to decreased the angle.

The oil in piston chamber (17) drains to the hydraulic tank through passages (21), (29), (27) and (23). The motor now holds the swashplate at its minimum angle position for small displacement.

Automatic Travel Speed Change Valve

Operation In Small Displacement Position

Automatic Travel Speed Change Valve (In Small Displacement Position)
(1) Displacement change valve. (2) Port. (3) Passage. (4) Pilot pump. (5) Shuttle valve. (6) Line. (7) Upper pump. (8) Lower pump. (9) Line. (10) Swivel. (11) Passage. (12) Solenoid valve (travel speed). (13) Line. (14) Line. (15) Automatic travel speed change valve. (16) Line. (17) Passage. (18) Passage. (19) Passage. (20) Passage. (21) Spring. (22) Spring chamber. (23) Spool. (24) Piston. (25) Piston chamber. (P_D) Main pump delivery pressure. (P_P) Pilot pump delivery pressure.

During the high travel speed mode, pilot pump delivery pressure (P_P) goes through travel speed solenoid valve (12) and line (13) to passage (18) of automatic travel speed change valve (15). The upper and lower main pump delivery pressure (P_D) from passages (3) and (11) combines at shuttle valve (5) and then goes through line (9) and passage (20) to piston chamber (25).

When main pump delivery pressure (P_D) in piston chamber (25) is low with a smaller load on the machine, spool (23) is pushed to the right by the force of spring (21) opening passage (19). Pilot pump delivery pressure (P_P) from line (13) goes through passages (18) and (19). Part of pilot pump delivery pressure (P_P) from passage (19) goes through passage (17) to spring chamber (22) and acts on spool (23). The remaining pilot pump delivery pressure (P_P) leaves valve automatic travel speed change valve (15) to line (14). Pilot pump delivery pressure (P_P) goes through swivel (10) and line (6) to displacement change valve (1). Displacement change valve (1) now activates to hold the swashplate of the travel motor at the minimum angle position for the small displacement.

Operation In Large Displacement Position

Automatic Travel Speed Change Valve (In Large Displacement Position)
(9) Line. (14) Line. (15) Automatic travel speed change valve. (16) Line. (19) Passage. (20) Passage. (21) Spring. (22) Spring chamber. (23) Spool. (24) Piston. (25) Piston chamber. (26) Passage. (27) Passage. (P_D) Main pump delivery pressure. (P_P) Pilot pump delivery pressure.

During travel at minimum displacement, main pump delivery pressure (Pd) in piston chamber (25) increases as the load increases on the machine. When main pump delivery pressure (Pd) increases to a certain level, piston (24) moves which causes spool (23) to move to the left against the combined forces of spring (21) and pilot pump delivery pressure (Pp) in spring chamber (22). Passage (19) closes and passage (26) opens. Passage (27) remains open to the hydraulic tank through line (16). Pilot pump delivery pressure (Pp) is blocked at passage (19) which blocks the connection between passage (13) and line (14). Pilot pump delivery pressure (Pp) in line (6) goes through line (14), passages (26) and (27), and returns to the hydraulic tank through line (16). Displacement change valve (1) returns to the off position which causes the swashplate of the travel motor to be held in its maximum angle position for maximum displacement.

During travel at maximum displacement of the travel motor, main pump delivery pressure (Pd) decreases with a decreased machine load. Automatic travel speed change valve (15) operates as described above for minimum displacement position.

Travel Brake Valve

Travel Brake Valve
(1) Crossover relief valve. (2) Spring. (3) Stem. (4) Passage. (5) Throttling slot. (6) Stem. (7) Cover. (8) Spring. (9) Crossover relief valve. (10) Passage. (11) Passage. (12) Passage. (13) Passage. (14) Passage. (15) Plunger chamber. (16) Passage. (17) Ball. (18) Spring. (19) Spring chamber. (20) Spool guide. (21) Passage. (22) Check valve. (23) Port. (24) Passage. (25) Passage. (26) Passage. (27) Port. (28) Spool. (29) Passage. (30) Check valve. (31) Spring. (32) Passage. (33) Counterbalance valve.

Each travel motor has a travel brake valve, consisting of counterbalance valve (33) and two crossover relief valves (1) and (9).

The travel brake valve is bolted to the travel motor. It functions to prevent the occurrence of a shock load at a travel stop operation, overrunning during traveling down a slope or cavitation. It also functions to send oil to the parking brake for brake release just before the start of machine movement.

Counterbalance Valve

Level Travel

Travel Motor And Travel Brake Valve (Left Track)
(1) Crossover relief valve (forward travel). (9) Crossover relief valve (reverse travel). (23) Port. (27) Port. (33) Counterbalance valve.

Under normal operation, pump oil to port (23) flows through passages (24) to spool (28). Pressure oil forces check valve (22) to open, allowing oil flow from port (22) through passages (11) and (10) to the piston of the travel motor. Oil then drives the travel motor.

A portion of pump oil in port (23) flows through passage (21) and into spring chamber (19). The oil then flows through passage (12) and check valve (17), and into plunger chamber (15). The oil in spring chamber (19) goes to the left end face of spool guide (20). Spool (28) moves to the right against the force of spring (31), opening throttling slot (5).

The motor return oil goes through passages (13) and (14), throttling slot (5) and passage (26), and out through port (27) to the hydraulic tank.

When oil flow from port (23) is blocked, there is a pressure decrease in both chambers (19) and (15). Spring (31) forces spool (28) to the left closing throttling slot (5). Return oil flow from the motor is blocked and the motor rotation stops.

If the travel direction is reversed, pump oil flows to spool (28) through port (27) and goes out through port (23). The operation is the same as described above.

During normal travel operation, counterbalance valve (33) remains inoperable.

Slope Travel

When the machine moves down a slope, the travel motors rotate at a higher speed due to machine mass (size and weight). The pumps cannot maintain the oil supply to the motors. The lack of pump oil supply will cause cavitation in the travel motors. A decrease in pressure (negative pressure) at port (23) results, causing a decrease in pressure in spring chamber (19). Spring (31) now forces spool (28) in counterbalance valve (33) to the left and begins to close throttling slots (5), blocking oil flow between passages (14) and (26). Both return oil flow to the hydraulic tank and oil flow to the travel motor suction port are restricted. Travel motor rotation slows down.

The lower pump oil pressure at port (23) now increases. Part of the oil goes to passage (21) and then flows as described in the section of "Level Travel". Spool (28) moves to the right, opening throttling slots (5). The modulation of spool (28) maintains the proper opening of throttling slots (5) when the machine goes down a slope. The motor now begins to rotate according to the amount of oil supplied from the pump and prevents the motor from cavitating.

When the machine moves down a slope, or stops, spool (28) suddenly closes throttling slots (5). A hydraulic pressure spike can occur. To prevent pressure spikes, a damper is provided at both ends of spool (28). As spool (28) returns to the left from its full open position, the oil in plunger chamber (15) is pressurized. Ball (17) moves to the right, closing passage (12) allowing the oil in plunger chamber (15) to go out through orifice (16) and into spring chamber (19). Movement of spool (28) slows down and slowly closes throttling slots (5).

Proper damper (cushion) effect is maintained by the size and position of orifice (16).

Crossover Relief Valve Operation

While the machine is slowing down and the travel control levers are moved back to NEUTRAL position to stop movement of the machine, there is no pump oil supplied to the travel motors and travel brake valves. A decrease in pressure now occurs at port (23) of the brake valve. Spring (31) returns spool (28) to the NEUTRAL position. The travel motor is still in rotation because of the mass (weight and size) of the machine in motion. Throttling slots (5) are closed, blocking the return oil. A sudden increase in pressure in passage (13) occurs. High pressure return oil in passage (13) goes through passage (4), opening stem (3) of crossover relief valve (1). The pressure oil from stem (3) goes to suction passage (10) of the travel motor.

Crossover relief valves (1) and (9) protect the travel motor against damage by allowing the high oil pressure to escape.

Crossover relief valves (1) and (9) allow makeup oil flow from the return side to the inlet side. This makeup oil helps to prevent a vacuum condition in the motor.

Crossover relief valves (1) and (9) activate in two-stage relief action to minimize the shock load when the travel motors stop. The operation of the valves is the same as that of the swing motor, described in swing control.

Crossover relief valve (1) opens just before a forward left travel stops and crossover relief valve (9) opens just before a reverse valve travel stops. Adjustment of crossover relief valve (1) or (9) with its track blocked, reverses the opened valve as follows.

During an adjustment where the left travel control lever is moved to the FORWARD LEFT TRAVEL position and the tracks are blocked, oil flow through passage (10) from port (23) is blocked. The oil pressure in passage (10) increases, opening stem (6). Oil now flows from passage (10) to passage (13). Crossover relief valve (9) opens and crossover relief valve (1) closes.

When the left travel control lever is moved to the REVERSE LEFT TRAVEL position, crossover relief valve (1) is open with crossover relief valve (9) closed in the same manner as described above.

Crossover relief valves (1) and (9) should be designated by their functions relative to the control lever movement during pressure adjustment. Call crossover relief valve (9) forward left travel and crossover relief valve (1) reverse left travel.

Parking Brake

When pump oil is supplied to port (23) to start the travel motor, spool (28) moves to the right to open passage (25).

Part of the oil in passage (24) goes through passages (25) and (32) to the travel motor parking brake for brake release. Since throttling slots (5) are opened only after passage (25) is opened, the travel motor does not operate before the brake is released.

When the supply of pressure oil to port (23) is blocked to stop the travel motor, spool (28) moves back to the NEUTRAL position, closing passage (25). Passage (25) is closed only after throttling slots (5) are closed. This allows the machine to stop movement before the parking brake is activated.

As described earlier in the section, "Parking Brake" of the travel motor, the oil from the brake piston chamber in the travel motor goes through the orifice in the brake releasing valve. Application of the brake is delayed.

The above operation releases the parking brake just before the travel motor starts rotation and engages the brake only after the motor has stopped. The parking brake is always kept released while the motor is rotating.

Oil Makeup

Oil Makeup Circuit
(1) Motor rotary group. (2) Left travel motor. (3) Passage. (4) Check valve. (5) Line. (6) Swivel. (7) Line. (8) Passage. (9) Left travel control valve. (10) Passage. (11) Return passage.

Return oil from the travel control valve is used as makeup oil to prevent a vacuum condition in travel motor when operation is stopped.

The oil makeup operation is given with respect to left travel. Operation is the same for right travel.

If the left travel control lever is returned to the NEUTRAL position to stop left travel, supply of pump oil to left travel motor (2) is blocked at passage (10). The motor continues to rotate because of the mass (weight and size) of the machine. A negative pressure at passage (3) of motor rotary group (1) opens check valve (4).

With left travel control valve (9) in NEUTRAL position, return oil from passage (11) flows to passage (8). The return oil then goes through line (7), swivel (6) and line (5) and enters left travel motor (2). The oil passes through opened check valve (4), passage (3), and into motor rotary group (1) as makeup oil. This makeup oil circuit eliminates the possibility of cavitation occurring in the travel motor.

Swivel

Swivel
(1) Retainer. (2) Cover. (3) Drain port. (4) Drain hole. (5) Port. (6) Seal. (7) Port. (8) Port. (9) Housing. (10) Port. (11) Port. (12) Flange. (13) Seal. (14) Rotor. (15) Plate. (16) Port. (17) Port. (18) Port. (19) Port. (20) Port. (21) Port. (22) Swivel. (23) Support. (24) Front direction.

Swivel (22) accomplishes two functions. One function is to supply pump oil from the upper structure (which swings) to the travel motors of the lower structure (which does not swing). It also functions to provide a means for oil from the motors (swing and travel) to return to the hydraulic tank.

Housing (9) is bolted to the upper structure through support (23). Rotor (14) is bolted to the lower structure through plate (15). The ports of housing (9) are open to the ports of rotor (14) through passages in housing (9) and rotor (14).

Seals (6) for high pressure and (13) for low pressure are provided between the sliding surfaces of housing (9) and rotor (14). Sends (6) and (13) prevent oil leakage between the passages.

Travel Drive

Travel Drive
(1) Bolt. (2) Roller bearing (2nd stage). (3) Planet gear (3rd stage). (4) Roller bearing (3rd stage). (5) Planet shaft. (6) Gear coupling. (7) Bolt. (8) Ball bearing. (9) Motor housing. (10) Travel motor. (11) Planet gear (2nd stage). (12) Planet shaft (2nd stage). (13) Planet shaft (1st stage). (14) Roller bearing (1st stage). (15) Planet gear (1st stage). (16) Sun gear (1st stage). (17) Cover. (18) Ring gear (1st stage). (19) Carrier (1st stage). (20) Sun gear (2nd stage). (21) Carrier (2nd stage). (22) Ring gear. (23) Sun gear (3rd stage). (24) Carrier (3rd stage). (25) Coupling. (26) Pin. (27) Output shaft (travel motor). (28) Sprocket housing.

The travel drive reduces the rotating speed of travel motor (10). Output shaft (27) is splined through coupling (25) to first stage sun gear (16) of the travel drive.

The travel drive consists of the following two groups:

1. Three-stage planetary gear reduction group.

First stage sun gear (16), first stage planet gears (15), first stage carrier (19) and ring gear (18) makeup the first stage. Second stage sun gear (20), second stage planet gears (11), second stage carrier (21) and ring gear (22) makeup the second stage. Third stage sun gear (23), third stage planet gears (3), third stage carrier (24) and ring gear (22) makeup the third stage.

2. Output group.

Rotation of sprocket housing (28) offers output torque for driving the track. The housing, ring gear (22) and cover (17) are held together with bolts (1). Ring gear (18) is bolted to cover (17). This integrated unit which is supported by ball bearings (8) turns together as ring gear (22) turns.

The planet reduction group functions to reduce the travel speed in a ratio of sun gear tooth numbers to ring gear tooth numbers. The compact travel drive with the sun gear incorporated in the ring gear housing provides a greater reduction ratio.

Planet Gear Operation

Rotation of travel motor output shaft (27) is transmitted to first stage sun gear (16). Sun gear (16) is splined to output shaft (27). When first stage sun gear (16) rotates clockwise (viewed from motor side), the travel drive assembly operates as described below.

First Stage Reduction Section
(13) Planet shaft (1st stage). (14) Roller bearing (1st stage). (15) Planet gear (1st stage). (16) Sun gear (1st stage). (18) Ring gear (1st stage). (19) Carrier (1st stage). (29) Rotating direction of 1st stage reduction group.

In the first stage reduction group, first stage planet gears (15) are in mesh with first stage sun gear (16). First stage planet gears (15) rotate counterclockwise as first stage sun gear (16) rotates clockwise. First stage planet gears (15) are also in mesh with ring gear (18). First stage planet gears (15) "walk" around the teeth of ring gear (18). As first stage planet gears (15) rotate, they circle around first stage sun gear (16) clockwise. First stage planet gears (15) are mounted to first stage carrier (19) by first stage planet shafts (13) and roller bearings (14). The assembly of first stage carrier (19) rotates clockwise.

Splines In Engagement
(13) Planet shaft (1st stage). (15) Planet gear (1st stage). (19) Carrier (1st stage). (20) Sun gear (2nd stage). (30) Splines in engagement.

Rotation of first stage carrier (19) is transmitted to second stage sun gear (20) of the second stage reduction group. The second stage reduction group is splined to first stage carrier (19). Second stage sun gear (20) rotates clockwise. Clockwise rotation of second stage sun gear (20) rotates second stage planet gears (11) counterclockwise. Second stage planet gears (11) are in mesh with second stage sun gear (20).

Since second stage planet gears (11) are also in mesh with ring gear (22), they "walk" around the teeth of ring gear (22). As second stage planet gears (11) rotate, they circle around second stage sun gear (20) clockwise. Second stage planet gears (11) are mounted to second stage carrier (21) by second stage planet shafts (12) and second stage roller bearings (2). The assembly of second stage carrier (21) rotates clockwise.

Splines In Engagement
(21) Carrier (2nd stage). (23) Sun gear (3rd stage). (31) Splines in engagement.

Second stage carrier (21) and third stage sun gear (23) are engaged with each other. Rotation of second stage carrier (21) is transmitted to third stage sun gear (23).

Splines on third stage carrier (24) engage with teeth on the outer circumference of motor housing (9) through gear coupling (6). With the housing held to the track frame, third stage carrier (24) cannot rotate. Unlike the first and second stage planet gears turning around their sun gears, third stage planet gears (3) turn on their own axes in the positions where they are mounted. This causes ring gear (22) to rotate counterclockwise.

Ring gear (22) and sprocket housing (28) are held together with bolts (1). The sprocket wheel is bolted to the housing. The torque of third stage sun gear (23) is transmitted to the housing, causing the sprocket to rotate counterclockwise. The right track rotates in the forward direction.

Straight Travel Operation

Straight travel (tracking) can be maintained even though there is a swing or implement operation during travel. Make reference to the section, "Straight Travel" for systems operation.

Straight Travel Control

Introduction

Main Control Valve Compartment
(1) Right travel. (2) Straight travel. (3) Left travel.

Hydraulic Schematic (Partial) (Only Travel Control Activated)
(1) Right travel control valve. (2) Straight travel control valve. (3) Left travel control valve. (4) Main control valves. (5) Line. (6) Line. (7) Upper pump. (8) Lower pump.

If the upper structure or implements are operated while the machine is traveling, straight travel control valve (2) assures a straight travel of the machine. Straight travel control valve (2) also allows better control of operations such as pipe laying or placement of timbers.

When the machine travels with no swing or implement operation, oil from upper pump (7) drives the right travel motor and oil from lower pump (8) drives the left travel motor. Since both travel circuits are separated, the machine continues to travel straight, unless a difference in travel resistance occurs between the right and left tracks.

Without the straight travel system, a swing and/or implement operation (while performing a travel operation) would cause upper pump (7) and lower pump (8) to supply varying amounts of pump oil to the track motors. This would cause the machine to not travel straight.

The straight travel system assures the machine to travel straight when circuits other than the travel circuits are simultaneously operated. When straight travel control valve (2) is activated by pilot pressure oil, the following occurs:

1. Upper pump (7) supplies oil not only to the right travel circuit but also to the left travel circuit to drive both motors in parallel.

2. The swing and implement circuits get their supply of pressure oil from lower pump (8). When the machine is traveling, the swing and implement circuits do not require a large amount of flow. They are operated at speeds low enough to keep the machine stable. The remainder of the pressure oil is divided between the right and left travel circuits.

Implement And Travel Operation

Hydraulic Schematic (Partial) (Boom and Travel Activated)
(1) Parallel feeder passage. (2) Main control valves. (3) Stick I control valve. (4) Swing control valve. (5) Left travel control valve. (6) Center bypass passage. (7) Right travel control valve. (8) Bucket control valve. (9) Boom I control valve. (10) Center bypass passage. (11) Passage. (12) Passage. (13) Passage. (14) Passage. (15) Straight travel valve. (16) Passage. (17) Passage. (18) Pilot passage. (19) Pilot passage. (20) Pilot passage. (21) Passage. (22) Passage. (23) Pilot passage. (24) Pilot passage. (25) Passage. (26) Parallel feeder passage. (27) Pilot oil manifold. (28) Upper pump. (29) Drain line. (30) Line. (31) Line. (32) Pilot pump. (33) Lower pump.

When the boom control lever is activated during travel, there is pilot oil flow from the travel pilot control valves through pilot passages (20) and (24) to right and left travel control valves (7) and (5). For a boom operation, pilot oil flows from the boom pilot control valve through pilot passage (23) to boom I control valve (9).

As the boom I control valve is operated, passage (22) is closed. There is an increase in pilot pressure in pilot passages (18) and (19). The increased pilot pressure operates straight travel valve (15).

Passage (25) connects in series stick I control valve (3), swing control valve (4), bucket control valve (8) and boom I control valve (9). If any of these valves is operated, the connection between passage (25) and passage (13), (14) or (21) closes. The pilot oil pressure in passages (18) and (19) increases high enough to operate straight travel control valve (15).

As long as all of the control levers for stick I control valve (3), swing control valve (4), bucket control valve (8) and boom I control valve (9) are in the NEUTRAL position, pilot passage (18) is connected to the pump suction line through passage (25) and drain line (29). The pilot pressure in pilot passages (18) and (19) is not enough to operate straight travel control valve (15).

When straight travel control valve (15) is operated, oil from both upper and lower pumps flows as follows so that the machine can travel straight:

1. Oil from upper pump (28) flows through line (30) to passage (17) in main control valves (2). Upper pump oil now flows in two paths. One path goes through center bypass passage (6) to right travel control valve (7). The other path goes through passage (12), straight travel control valve (15) and center bypass passage (10) to left travel control valve (5). The right and left travel motors now get an equal amount of upper pump oil.

2. Oil from lower pump (33) flows through line (31) to passage (16) in main control valves (2). Lower pump oil now flows in two paths. One path goes through parallel feeder passage (1) to the valves for swing control (4) and stick I control (3). The other path goes through passage (11) and straight travel control valve (15) to parallel feeder passage (26). The oil in parallel feeder passage (26) then goes to bucket control valve (8) and boom I control valve (9).

A portion of the lower pump oil in passage (11) goes through the check valve and orifice in straight travel valve (15), combining with the upper pump oil at center bypass passage (10). This helps drive both right and left travel motors.

Straight Travel Control Valve

Straight Travel Valve (Neutral Position)
(1) Parallel feeder passage. (2) Center bypass passage. (3) Center bypass passage. (4) Parallel feeder passage. (5) Pilot passage. (6) Piston chamber. (7) Spring. (8) Passage. (9) Line. (10) Line. (11) Passage. (12) Stem. (13) Straight travel control valve. (14) Upper pump. (15) Lower pump.

When there is only a travel operation, pilot pressure in pilot passage (5) is kept low. The oil pressure in piston chamber (6) also remains low. Stem (12) is pushed all the way to the right by the force of spring (7). Oil from both upper and lower pumps flows as follows.

1. Oil from upper pump (14) goes through line (10) to passage (11) in straight travel control valve (13). The upper pump oil now flows in two paths. One path goes through center bypass passage (3) and into the right travel control valve. The other path goes through parallel feeder passage (4) and into the bucket, attachment and boom I control valves.

2. Oil from lower pump (15) goes through line (9) to passage (8) in straight travel control valve (13). The lower pump oil then flows in two paths. One path goes through parallel feeder passage (1) and into the swing, stick I and boom II control valves. The other path goes through center bypass passage (2) and into the left travel control valve.

Straight Travel Valve (Activated Position)
(1) Parallel feeder passage. (2) Center bypass passage. (3) Center bypass passage. (4) Parallel feeder passage. (5) Pilot passage. (6) Piston chamber. (7) Spring chamber. (8) Passage. (9) Line. (10) Line. (11) Passage. (12) Stem. (13) Straight travel control valve. (14) Upper pump. (15) Lower pump. (16) Check valve. (17) Passage. (18) Passage. (19) Orifice.

When a travel and implement (or swing) operation occurs, pilot oil pressure in pilot passage (5) increases. The oil pressure in piston chamber (6) increases enough to shift stem (12) to the left against the force of spring (7). Pump oil now flows as follows:

1. The upper pump oil goes through passage (11) and then flows in two paths. One path goes through center bypass passage (2) to the left travel control valve. The other path goes through center bypass passage (3) to the right travel control valve.

2. The lower pump oil goes through passage (8) and flows in two paths. One path goes through parallel feeder passage (1) and enters the swing, stick I and boom II control valves. The other path goes through passage (17) and parallel feeder passage (4) to the bucket, attachment and boom I control valves.

Part of the lower pump oil in passage (17) goes through orifice (19), check valve (16) in stem (12), passage (18) and to center bypass passage (2). The lower pump oil then combines with the upper pump oil. The combined upper and lower pump oil is used to help drive both the right and left travel motors.

Loading Operation

Introduction

Combined Operations Of Boom Raise, Stick Out And Swing Right

Combined Operations Of Boom Lower, Stick Out and Swing Left

With the bucket loaded (or filled), it is moved to the dump location by a simultaneous (at the same time) operation of boom raise, stick out and swing. After the bucket is unloaded at the dump location, it is moved to the original excavating position by a simultaneous operation of boom lower, stick out and swing. This is one cycle of the loading operation.

For loading operations, work mode selector switch (2) should be placed in BOOM PRIORITY MODE (1) position. This activates the selector valve and logic valve. Depending on whether the boom is raised or lowered, the flow rate of oil from both pumps to the implement and swing motors varies.

During a boom raise operation, boom and stick circuits share upper pump oil. The lower pump oil is supplied to stick, swing and boom circuits.

During a boom lower operation, all of lower pump oil is supplied to the swing and stick circuits and all of upper pump oil is supplied to the boom and stick circuits.

Better loading operation is assured during a combined operation of boom, stick and swing.

Right Console (Switch Panel)
(1) BOOM PRIORITY MODE position. (2) Work mode selector switch.

Combined Loading Operations

Boom Raise, Stick Out And Swing Right

Schematic (Partial) (Boom Raise, Stick Out And Swing Right)
(1) Line. (2) Line. (3) Line. (4) Pilot line. (5) Pilot passage. (6) Parallel feeder passage. (7) Boom I control valve. (8) Stick II control valve. (9) Boom II control valve. (10) Pilot passage. (11) Stick I control valve. (12) Passage. (13) Logic valve. (14) Passage. (15) Swing control valve. (16) Passage. (17) Pilot passage. (18) Passage. (19) Line. (20) Pilot passage. (21) Drain passage. (22) Pressure control valve. (23) Parallel feeder passage. (24) Pilot passage. (25) Selector valve. (26) Pilot passage. (27) Upper pump. (28) Lower pump. (29) Pilot pump.

In a loading operation involving boom raise, stick out and swing right, pilot pump (29) oil is used as follows:

1. In boom raise, pilot oil is supplied to boom I control valve (7) and boom II control valve (9) through pilot passages (24) and (10), respectively.

2. In stick out, pilot oil is supplied to stick I control valve (11) and stick II control valve (8) through pilot passages (4) and (17), respectively.

3. In swing right, pilot oil is supplied through pilot passage (5) to swing control valve (15).

With the work mode selector switch in BOOM PRIORITY MODE position, pilot oil goes through passage (20) to pressure control valve (22).

When pilot oil is supplied to the above valves, each valve activates as follows.

1. Pilot oil pressure from pilot passage (10) shifts boom II control valve (9) making an open connection between parallel feeder passage (6) and line (1).

2. Pilot oil pressure from pilot passage (20) shifts pressure control valve (22) making an open connection between passage (14) and drain passage (21). Because the pilot oil pressure from parallel feeder passage (6) is greater than the pilot oil pressure in pilot passage (4), logic valve (13) shifts to the open position.

3. Pilot pressure oil from pilot passage (17) shifts stick II control valve (8) making an open connection between passages (16) and (18). Pressure oil from pilot passage (26) opens selector valve (25).

Now, oil from upper and lower pumps flows as follows.

The upper pump (27) oil goes through parallel feeder passage (23) and then separates into two oil paths. One path goes through boom I control valve (7), line (3) and line (2) to the boom cylinders. The other path goes through selector valve (25), line (19) and passage (12), and through stick I control valve (11) to the stick cylinder.

The lower pump (28) oil flows through parallel feeder passage (6) and then separates into the following three oil paths.

1. One path goes through swing control valve (15) to the swing motor.

2. Another path goes through logic valve (13) and then combines with the upper pump oil in passage (12). The oil then goes through stick I control valve (11) to the stick cylinder.

3. The third path goes through boom II control valve (9) to line (1). The oil then combines with the upper pump oil in line (2) and goes to the boom cylinders.

In this type of a loading operation, the boom and stick cylinders are always supplied both upper and lower pump oil. This moves the boom up at a faster speed to clear the excavation site after digging. The swing motor is supplied an appropriate amount of lower pump oil, assuring an optimum swing speed. If swing movement is too fast, the bucket would reach the side of the dump unit before the boom is raised high enough to clear the side.

Boom Lower, Stick Out And Swing Left

Schematic (Partial) (Boom LOWER, Stick OUT And Left Swing)
(6) Parallel feeder passage. (7) Boom I control valve. (8) Stick II control valve. (9) Boom II control valve. (11) Stick I control valve. (12) Passage. (13) Logic valve. (15) Swing control valve. (19) Line. (23) Parallel feeder passage. (25) Selector valve. (27) Upper pump. (28) Lower pump. (29) Pilot pump.

During a loading operation involving boom lower, stick out and swing left, the pilot oil operates stick I control valve (11), swing control valve (15), boom I control valve (7) and stick II control valve (8). Selector valve (25) and logic valve (13) are kept opened in the same manner as that described previously.

With boom II control valve (9) in the NEUTRAL position, pilot oil flow through parallel feeder passage (6) is blocked by boom II control valve (9).

Now, oil from upper and lower pumps flows as follows:

Upper pump (27) oil flows through parallel feeder passage (23) and then separates into two oil paths. One path goes through boom I control valve (7) to the boom cylinders. The other path goes through selector valve (25), line (19) and stick I control valve (11) to the stick cylinder.

Lower pump (28) oil flows through parallel feeder passage (6) and then separates into two oil paths. One path goes through swing control valve (15) to the swing motor. The other path goes through logic valve (13) and stick I control valve (11) to the stick cylinder.

Now, less upper pump oil is required for the boom cylinders because the regeneration circuit activates during a boom lower operation. The remainder of the upper pump oil is used for a stick raise operation. The lower pump oil is shared by the swing and stick circuits in an optimum manner. A better loading operation is assured during a combined operation of boom lower, stick out and swing left.

Leveling Operation

Introduction

The purpose of a leveling operation is to level a ground surface with high accuracy using the combined movement of the boom and stick. During a leveling operation, the boom and stick make fine movements to keep the tip of the bucket against the ground surface.

Stick In Leveling (Movement Of Boom And Stick)

Right Console (Switch Panel)
(1) Power mode selector switch. (2) Fine control mode. (3) Work mode selector switch. (4) Power mode I.

Since leveling operations are slow speed work, power mode selector switch (1) is turned to MODE I position (4) for light work. Also, work mode selector switch (3) is turned to FINE CONTROL MODE position (2) to keep the boom and stick operating circuits separated at a reduced rate of flow.

For leveling operation, the movement of stick in and boom raise is combined. In this operation, the boom and stick circuits are supplied pump oil from the upper and lower pumps. Since the boom and stick circuits now have an individual pump oil supply designated to their function, the operation of the boom and stick cylinders will not have any affect on each other.

Fine Control Circuit

Schematic (Partial)
(1) Stick cylinder. (2) Boom cylinder. (3) Center bypass passage. (4) Boom I control valve. (5) Stick II control valve. (6) Pilot line. (7) Pilot passage. (8) Boom II control valve. (9) Passage. (10) Center bypass passage. (11) Passage. (12) Check valve. (13) Line. (14) Pilot passage. (15) Stick I control valve. (16) Pilot passage. (17) Parallel feeder passage. (18) Pilot passage. (19) Selector valve. (20) Pilot passage. (21) Pilot control valve (stick). (22) Solenoid valve (fine control). (23) Line. (24) Upper pump. (25) Line. (26) Lower pump. (27) Pilot pump. (28) Hydraulic tank.

When the boom and stick control levers are slowly moved to the BOOM RAISE and STICK IN position, pilot pump (27) oil is used as follows.

1. In the BOOM RAISE position, pilot oil is supplied to boom I control valve (4) and boom II control valve (8) through pilot passages (18) and (14), respectively.

2. In the STICK IN position, pilot oil is supplied to stick I control valve (15) and boom II control valve (8) through pilot passages (16) and (7), respectively.

With the work mode selector switch in FINE CONTROL position, fine control solenoid valve (22) is energized, causing no pilot oil flow to pilot line (6).

When pilot oil is supplied to the above valves, each valve activates as follows.

1. Boom II control valve (8) is in the NEUTRAL position because the pilot pressure acting on its both end ports is equal. A portion of lower pump oil goes through center bypass passage (10) and boom II control valve (8) and returns to hydraulic tank (28).

2. With fine control solenoid valve (22) energized, pilot oil flow from pilot control valve (21) through line (25) is blocked at the inlet port of fine control solenoid valve (22). There is no pilot oil sent from pilot line (6) to stick II control valve (5). Stick II control valve (5) is held in the NEUTRAL position. A portion of the upper pump oil returns to hydraulic tank (28) through center bypass passage (3).

3. When the boom control lever is partially moved to BOOM RAISE position, the stem of boom I control valve (4) partially shifts. In boom I control valve (4), the opening of passage (11) is slightly opened while the opening of center bypass passage (3) is slightly closed. This causes an appropriate amount of upper pump oil to go to boom cylinders (2) and the remainder of the upper pump oil to go back to hydraulic tank (28). Depending on the travel distance of the boom control lever, the upper pump oil is metered to boom cylinders (2) for fine control operation of the boom cylinders.

4. The stem of stick I control valve (15) also partially shifts. In the same manner as that described for boom cylinders (2), the lower pump oil is metered to stick cylinder (1) for fine control operation of the stick cylinder.

5. Since center bypass passage (3) is open to hydraulic tank (28), the oil pressure in center bypass passage (3) (during a fine control operation) does not increase enough to open check valve (12). There is no upper pump oil flow through line (13) to stick I control valve (15).

6. With stick II control valve (5) in the NEUTRAL position, there is no oil flow from parallel feeder passage (17) to pilot passage (20). Selector valve (19) remains closed, causing no oil flow from parallel feeder passage (17) to line (13).

NOTE: Items 1, 2, 3 and 4 described above provide fine control operations of the boom and stick. Items 5 and 6 describe how the boom and stick circuits are separated. Movement of one cylinder does not affect the movement of the other during fine control operation of the boom and stick.

Trenching Operation

Introduction

Trenching Operation (Illustration Of Applied Swing Force)

When excavating a ditch, its cross section should be rectangular. The force of the ditch wall acting against the bucket, causes the bucket to move away from the wall of the ditch.

Right Console (Switch Panel)
(1) Power mode selector switch. (2) SWING PRIORITY MODE position. (3) Work mode selector switch.

To get a straight (vertical) wall, it is necessary that an additional side force be used to hold the bucket against the side wall. The operator does this by applying partial swing in the direction of the wall.

When work mode selector switch (3) is placed in SWING PRIORITY MODE position (2), the swing priority solenoid valve is energized, activating the selector valve and logic valve. Upper pump oil goes to the circuits for the boom, stick and bucket. Lower pump oil goes to only the swing circuit. Now, the pressure of the swing circuit remains high enough to provide a force against the side wall.

Place power mode selector switch (1) in either of positions I, II or III, depending on the work to be done.

A trenching operation is done by combined operation of boom raise, stick in, bucket close and swing.

Trenching Operation (Swing Priority Solenoid Valve Energized)

Hydraulic Schematic (Partial) (Swing Priority Operation)
(4) Pilot passage. (5) Pilot passage. (6) Line. (7) Pilot passage. (8) Bucket control valve. (9) Boom I control valve. (10) Stick II control valve. (11) Stick I control valve. (12) Parallel feeder passage. (13) Logic valve. (14) Boom II control valve. (15) Pilot passage. (16) Swing control valve. (17) Pilot passage. (18) Passage. (19) Parallel feeder passage. (20) Pilot passage. (21) Pilot passage. (22) Selector valve. (23) Pilot passage. (24) Drain passage. (25) Pressure control valve. (26) Drain passage. (27) Solenoid valve (swing priority). (28) Upper pump. (29) Pilot pump. (30) Lower pump.

When the control levers are moved to either the BOOM RAISE, STICK IN, BUCKET CLOSE or SWING RIGHT position, pilot pump (29) oil is used as follows.

1. In the BOOM RAISE position, pilot oil is supplied to boom I control valve (9) and boom II control valve (14) through pilot passages (21) and (15), respectively.

2. In the STICK IN position, pilot oil is supplied to stick I control valve (11), stick II control valve (10) and boom II control valve (14) through pilot passages (17), (7) and (4), respectively.

3. In the BUCKET CLOSE and SWING RIGHT position, pilot oil is supplied to bucket control valve (8) and swing control valve (16) through pilot passages (20) and (5), respectively.

With work mode switch (3) in SWING PRIORITY MODE position (2), swing priority solenoid valve (27) is energized, making an open connection between pilot passage (23) and drain passage (26).

Now each valve activates as follows.

1. The pilot oil pressure acting at both end ports of boom II control valve (14) is equal. Boom II control valve (14) remains in the NEUTRAL position, blocking oil flow from parallel feeder passage (12).

2. With pilot passage (23) open to drain passage (26), pressure control valve (25) shifts, closing the connection between passage (18) and drain passage (24). The oil in passage (18) is blocked. Now logic valve (13) remains closed, allowing no oil flow from parallel feeder passage (12) to stick I control valve (11).

3. When stick II control valve (10) is shifted by pilot passage (7), selector valve (22) opens.

NOTE: See the section, "Loading Operation".

Now, all of lower pump (30) oil goes from parallel feeder passage (12) through swing control valve (16) to the swing motor. The swing motor uses its torque only for holding the bucket against the side wall and does not rotate. All of the oil supplied to the swing motor is vented through the relief valve of the swing motor when swing pressure reaches the relief setting of 27500 kPa (4000 psi). This increases the motor torque to securely hold the bucket against the side wall.

The upper pump (28) oil in parallel feeder passage (19) separates into three oil paths. One path goes through bucket control valve (8) to the bucket cylinder. Another path goes through boom I control valve (9) to the boom cylinders. The third path goes through selector valve (22), line (6) and stick I control valve (11) to the stick cylinder.