Introduction

Reference: For Specifications with illustrations, make reference to the Specifications For Backhoe Loaders, Form No. SENR3194. If the Specifications given in Form SENR3194 are not the same as given in the Systems Operation and the Testing and Adjusting, look at the printing date on the back cover of each book. Use the Specifications given in the book with the latest date.

General Description

Hydraulic Schematic
(1) Right stabilizer cylinder. (2) Stick cylinder. 3. Backhoe bucket cylinder. (4) Right side swing cylinder. (5) Left side swing cylinder. (6) Left side boom cylinder. (7) Right side boom cylinder. 8. Left stabilizer cylinder. (9) Backhoe control valve group. (10) Loader control valve group. (11) Right side lift cylinder. (12) Left side lift cylinder. (13) Loader bucket tilt cylinder. (14) Hydraulic tank. (15) Pump. (16) Steering cylinder. (17) Hand metering pump. (A) Inlet manifold. (B) Extendable stick valve (option). (C) Right stabilizer valve section. (D) Stick control valve control section. (E) Backhoe bucket tilt control section. (F) Swing cylinder valve section. (G) Boom control. (H) Left stabilizer valve section. (I) Auxiliary equipment valve (option). (K) Loader inlet and steering priority. (L) Multi-purpose bucket valve (option). (M) Lift control valve section. (N) Tilt control valve section.

The hydraulic system controls the operations of steering, the backhoe, the loader and the stabilizers. The basic hydraulic system has a hydraulic tank (14) with a stacked two-element filter. It has a variable displacement axial-piston pump (15). It has a loader valve group (10), a loader bucket tilt cylinder (13) and two loader lift cylinders (11) and (12). The basic system also has a backhoe valve group (9), a right stabilizer cylinder (1), a left stabilizer cylinder (8), a stick cylinder (2), a backhoe bucket cylinder (3), a right swing cylinder (4), a left swing cylinder (5) and two boom raise cylinders (6) and (7). The basic system also has steering hand metering unit (HMU) (17) and a steering cylinder (16).

Reference: See Backhoe Loaders Steering System And Front Axle, Form No. SENR3159.

Optional equipment for the loader hydraulic system includes the multi-purpose bucket valve section (L) and cylinder.

Hydraulic Components
(2) Stick cylinder. (3) Backhoe bucket cylinder. (5) Swing cylinder. (7) Boom cylinder. (8) Stabilizer cylinder. (9) Backhoe control valve group (along back of cab). (10) Loader control valve group (operator's right side). (11) Lift cylinder. (13) Loader bucket tilt cylinder. (14) Hydraulic tank. (15) Pump. (16) Steering cylinder. (17) Hand metering pump.

Optional equipment for the backhoe hydraulic system includes an extendable stick valve section (B) and cylinder (not shown). Without the extendable stick, this group can be used with a hammer. Also optional for the backhoe circuit is an auxiliary equipment valve section (I). This group can control an attachment like a clam added to the extendable stick. Finally there are three optional backhoe control lever designs.

Standard Controls

NOTE: The terms right and left shall be determined by the position of the operator when seated in either the loader operating position or the backhoe operating position.

Front Of Tractor (416)
(15) Pump. (18) Compensator valve. (19) Line from hydraulic tank. (21) Supply line to control valves. (22) Resolver network line to compensator valve.

Loader Valve Group
(K) Loader inlet and steering priority valve. (L) Multi-purpose bucket valve (option). (M) Lift control valve section. (N) Tilt control valve section. (P) Cover.

This hydraulic system is a load-sensing and pressure-compensated, closed-centered system. Pump (15) has a compensator valve (18) attached. When none of the hydraulic circuits are being used, the pump is at low pressure standby. If one or more circuits are being used, a resolver network compares the control valve work port pressures. The single highest pressure felt goes to the pump compensator valve (18). This valve now keeps the pumps flow at a level needed to fulfill system flow and pressure requirements. The actual system pressure will be greater than the highest work port pressure requirements unless the pump is at full stroke. This difference between work port need and the higher supply pressure is called margin pressure. The compensator valve also limits maximum system pressure. This protects the hydraulic system from damaging high pressures.

Backhoe Valve Group
(A) Inlet manifold. (B) Extendable stick (option). (C) Right stabilizer. (D) Stick valve. (E) Bucket tilt valve. (F) Swing cylinder valve. (G) Boom control valve. (H) Left stabilizer. (I) Auxiliary valve (option). (J) Cover.

When driving the machine, the operator is facing forward. Loader controls are at his right side.

Loader Control Levers
(23) Single lever (raise, lower, tilt back, dump). (24) Multi-purpose bucket control lever (option).

To operate the backhoe the operator must slide the seat toward the rear of the machine. Then he must rotate the seat 180°. Backhoe levers are now before him.

Backhoe Control Levers
(25) Single lever boom controls (up, down, right, left). (26) Left stabilizer. (27) Right stabilizer. (28) Stick controls (out, in, load, dump).

Tank And Filters

The hydraulic oil tank is located in front of the radiator. The tank is sealed (air tight). Tank oil capacity is 36 liters (9.5 gal.). Tank air capacity is 44 liters (12 gal.). Total tank capacity is 80 liters (21 gal.). Since the tank is sealed, contamination is prevented. This also prevents overfilling as air above the filler tube cannot escape. The filler tube screen (2) helps to minimize dirt from entering the tank. Sight glass (1) is on the left side of the tank. The oil filter assembly is located inside the tank. Filter bypass valve (9) is set at 138 kPa (20 psi) for filter protection. This valve is below the filter assembly inside the tank. Filler cap (3) allows the compressed air inside the tank to escape before the cap is totally removed.

Hydraulic Tank
(1) Sight glass. (2) Filler screen. (3) Fill cap. (4) Pump case drain. (5) Pump case drain filter. (6) Spacer plate. (7) Return oil filter. (8) Line to pump. (9) Filter bypass valve. (10) Return oil. (11) Bypass valve. (12) Spring.

The oil filter assembly is inside the hydraulic tank. There are two stacked filters, separated by a plate.

Pump case return oil enters the tank through line (4). The oil fills the inside of filter (5). Plate (6) prevents this oil from going into filter (7). The pump case return oil is filtered as it flows through the filter element to tank. Filter (5) stops debris if a pump failure should occur. Implement and steering system return oil enters the tank through passage (10). The oil is forced up into filter (7). Plate (6) prevents this oil from going to filter (5). The oil now flows through the filter element to the tank, and filter (7) removes debris.

If filter (7) becomes full of debris, the flow restriction causes a pressure increase inside the filter. The pressure oil causes bypass valve (11) to move against the force of spring (12). The oil then goes past the open bypass valve into the tank. When return oil does not go through the filter elements, debris in the oil will cause damage to other components in the hydraulic system.

Correct maintenance must be used to make sure that filter elements (7) and (5) do not become full of debris.

Hydraulic Oil Cooler

Cooler
(1) Oil cooler. (2) Bypass valve.

A hydraulic oil cooler (1) with bypass valve (2) is available on the 416. The cooler is primarily intended for use with an auxiliary hydraulic hammer. Bypass valve (2) opens at about 170 KPa (25 psi). If added, the cooler bolts to the top front of the radiator. A hydraulic oil cooler with bypass valve is standard on 426 and 436 Backhoe Loaders. All of the return oil in the hydraulic system flows through the hydraulic oil cooler. The oil cooler is mounted on the front center of the radiator behind the hydraulic tank. The oil cooler is necessary because of the higher hydraulic power capability (ie. higher oil flow, larger cylinders) of the 426 and 436 Backhoe Loaders.

Hydraulic Pump 4T6895/9T6857

The pump for the hydraulic system is an automatically controlled, piston-type pump. It senses both pressure and flow needs. The pump is in front of the engine and below the hydraulic tank. It is connected to the engine crankshaft pulley by a drive shaft and flexible coupling assembly. The pump is mounted to a cast iron bracket. The bracket is bolted to the lower part of the engine.

Hydraulic Pump Lines (416)
(21) Pump outlet to control valves. (22) System return to tank. (23) Signal line pressure tap. (24) Pump outlet pressure tap. (25) Supply line from tank. (26) Case drain line to tank. (27) Signal line from backhoe, loader and steering valves.

Variable Displacement Piston Pump And Compensator Valve (4T6895)
(1) Swashplate. (2) Port plate. (3) Compensator valve. (4) Drive shaft. (5) Shoe plate. (6) Piston shoe. (7) Piston. (8) Cylinder barrel. (9) Plug. (10) Seat. (11) Seat. (12) Chamber for load pressure. (13) Pressure compensator spool. (14) Drain passage to pump case. (15) Flow compensator spool. (16) Passage to swashplate control piston. (17) Passage to pump outlet. (18) Signal passage. (19) Actuator piston. (20) Spring.

When drive shaft (4) is rotated, cylinder barrel (8) also turns. Nine pistons (7) are held in and turn with cylinder barrel (8). Each piston has an attached piston shoe (6). These shoes are held against the nonrotating swashplate (1) by shoe plate (5). At maximum swashplate angle (above) the pistons in position (A) are pulled out of cylinder barrel (8). This pulls oil from the inlet port through port plate (2) into the piston bore in cylinder barrel (8). As this barrel rotates to position (B), the angled swashplate pushes the pistons back into the cylinder barrel. This pushes oil out of the piston bore, through port plate (2) and into the output port.

The angle of the swashplate determines how much oil is drawn into each piston bore. The angle therefore determines how much oil is pushed or pumped out of each piston bore per drive shaft rotation. There are infinite swashplate angle positions between neutral (zero degrees or straight up and down) and the maximum angle. The greater the swashplate angle, the greater the amount of oil pulled into the pump and the greater the amount of oil discharged through port plate (2) to the output port.

When swashplate (1) angle is minimum, pistons (7) do not move in and out of the rotating cylinder barrel. Therefore, no oil is drawn into the pump and no oil is pushed or pumped out of the pump. There is zero displacement from the pump. The pump is not generating oil flow.

The pump has a compensator valve (3) that keeps pump pressure and flow at a level needed to fulfill the system load and flow needs. The compensator valve does this by either sending pump oil to or draining oil from actuator piston (19). This piston works with the swashplate control spring (20) to continually adjust the swashplate angle. Pump outlet pressure is kept about 1380 kPa (200 psi) above work port pressure needs. The compensator valve also has a pressure limiting ability that prevents pump and system overloads. When work port pressure goes over 19 000 kPa (2750 psi), pressure compensator spool (13) will override flow compensator spool (15) and lower pump output. This action starts at about 690 kPa (100 psi) below the maximum pressure setting.

The following schematics show how the pump and its compensator valve act during different conditions in the hydraulic system.

Upstroking

Pump And Compensator Operation
(1) Pressure compensator spring. (2) Flow compensator spring. (3) Cavity. (4) Signal line. (5) Flow compensator spool. (6) Actuator piston. (7) Case drain. (8) Actuator spring. (9) Swashplate. (10) Passage. (11) Line. (12) Passage. (13) Orifice from cavity (15). (14) Pressure compensator spool. (15) Pressure compensator cavity. (16) Plug.

Upstroking is when the pump is increasing displacement (output). This occurs when the signal pressure increases due to a high load (implement or steering) at low pump output. The highest resolved signal pressure (see SIGNAL RESOLVER NETWORK) goes through line (4) and fills cavity (3). Now the signal pressure, plus the force of spring (2), moves spool (5) down. This lets the oil behind actuator piston (6) go to case drain (7). The force of actuator spring (8) is now greater than the force behind the actuator piston. Swashplate (9) angle increases. This increases pump output. The pump output pressure increases until the pressure in passage (12) moves spool (5) up to the metering position. Initially, in the metering position (Figure 1), pump pressure is greater than the combined force of spring (2) and the signal pressure in cavity (3). Spool (5) moves up. Pump pressure is now sent to actuator piston (6). This overcomes the force of actuator spring (8). Swashplate (9) angle decreases. Pump output decreases. When pump pressure reduces enough, the combined signal and spring force in cavity (3) moves spool (5) down (Figure 2). The oil pressure behind actuator piston (6) goes back to case drain per previous discussion. Spring (8) forces swashplate (9) angle to increase. This slight up and down spool movement is called metering. Metering keeps the pressure on both ends of spool (5) equal. Spring (2) is equal to 1380 kPa (200 psi). Therefore, pump pressure is 1380 kPa (200 psi) greater than signal pressure. This difference is called margin pressure.

Metering Position

Destroking

Pump And Compensator Operation
(1) Pressure compensator spring. (2) Flow compensator spring. (3) Cavity. (4) Signal line. (5) Flow compensator spool. (6) Actuator piston. (7) Case drain. (8) Actuator spring. (9) Swashplate. (10) Passage. (11) Line. (12) Passage. (13) Orifice from cavity (15). (14) Pressure compensator spool. (15) Pressure compensator cavity. (16) Plug.

Destroking is when the pump is decreasing displacement (output). This occurs when the signal pressure decreases due to a low load (implement or steering) at high pump output. The lower signal pressure goes through line (4) and fills cavity (3). Now the signal pressure, plus the force of spring (2) in cavity (3), is less than the pump pressure in passage (12). Spool (5) is pushed up. Oil behind actuator piston (6) cannot go to case drain (7). Pump oil now flows through passage (12), past spool (5) and into actuator piston (6). Pump pressure behind actuator piston (6) is now greater than the force of spring (8). Swashplate (9) angle decreases. This decreases pump output. Passage (12) pressure will become less than the combined force in cavity (3). Spool (5) will now move down to the metering position. As long as the signal pressure stays the same, spool (5) will remain in the metering position. The hydraulic system is now stabilized (equalized).

NOTE: See Upstroking discussions on the preceding pages for an explanation of metering.

High Pressure Stall

Pump And Compensator Operation
(1) Pressure compensator spring. (2) Flow compensator spring. (3) Cavity. (4) Signal line. (5) Flow compensator spool. (6) Actuator piston. (7) Case drain. (8) Actuator spring. (9) Swashplate. (10) Passage. (11) Line. (12) Passage. (13) Orifice from cavity (15). (14) Pressure compensator spool. (15) Pressure compensator cavity. (16) Plug.

High pressure stall is when the hydraulic system stalls out under load or when the cylinders reach the end of the stroke. Stall occurs when pump output reaches 19 000 kPa (2750 psi). Signal pressure in line (4) now equals pump output pressure. Spring (2) now moves spool (5) down. This 19 000 kPa (2750 psi) pressure also moves spool (14) up against the force of spring (1). Now pump oil goes past spool (14) and spool (5) to the back of actuator piston (6). Swashplate (9) moves right against the force of spring (8). Pump output (flow) now decreases while system pressure stays at 19 000 kPa (2750 psi) (zero flow and maximum pressure).

If the control valve is moved to HOLD during high pressure stall, the signal pressure in cavity (3) flows through signal line (4) to the control valve where it returns to tank. System pressure begins to bleed down. At approximately 18 350 kPa (2650 psi), spring (1) moves pressure compensator spool (14) down and the system pressure in passage (12) acts against the force of spring (2) to move flow compensator spool (5) up. Supply oil flows past compensator spool (5) to actuator piston (6). Actuator piston (6) keeps the pump destroked until system pressure decreases. As the system pressure approaches 1720 kPa (250 psi) (low pressure standby), flow compensator spool (5) moves down to the metering position. Swashplate (9) will maintain a slight angle that is sufficient to make up for system leakage and provide the lower required pressure.

Low Pressure Standby

Pump And Compensator Operation
(1) Pressure compensator spring. (2) Flow compensator spring. (3) Cavity. (4) Signal line. (5) Flow compensator spool. (6) Actuator piston. (7) Case drain. (8) Actuator spring. (9) Swashplate. (10) Passage. (11) Line. (12) Passage. (13) Orifice from cavity (15). (14) Pressure compensator spool. (15) Pressure compensator cavity. (16) Plug.

Low pressure standby is when the machine is on, the implements are in hold and steering is not being used. There are no flow or pressure demands on the pump. Therefore, there is no signal pressure in line (4).

Before the engine is started, actuator spring (8) holds swashplate (9) at maximum angle. As the pump begins to turn, making oil flow, pressure builds in the system because of the closed-center implement valves. This pressure in passage (12) is felt at the bottoms of both pressure compensator (14) (pressure limiter) and flow compensator (5) (margin) spools. As this pressure increases, it pushes the flow compensator (margin) spool up against its spring. When system pressure becomes greater than 1380 kPa (200 psi) spool (5) will have moved up far enough to open up a passage for pressure oil to the back of actuator piston (6). This causes the actuator piston to move to the right which compresses actuator spring (8) and moves the swashplate toward minimum angle. The actuator piston continues to move to the right until it uncovers the cross-drilled passage of the actuator piston rod, allowing oil to drain to case.

At this point, pump output flow is not enough to make up for normal system leakage, the additional leakage through the cross-drilled hole, and to further increase oil pressure behind the actuator piston to continue moving it to the right. This limits the maximum travel of the piston to the right. The piston will now move slightly to the left until only part of the cross-drilled hole is open to case. At this point, the pump is producing enough flow to make up system leakage and leakage to the pump case through the cross-drilled hole while maintaining system pressure at 1725 kPa (250 psi).

The pump is at low pressure standby. This pressure is different than margin pressure because of system leakage and the cross-drilled hole in the actuator piston rod. The flow compensator (margin) spool, instead of metering oil, must remain open and move up higher against spring (2) to provide enough flow to the back side of the actuator piston to make up the leakage through the cross-drilled hole. This flow must be enough to maintain the pressure required at the back of the piston to overcome the actuator spring. System pressure must be approximately 345 kPa (50 psi) higher than margin pressure to shift the spool up this additional amount against spring (2). Oil pressure behind the actuator piston is less than system pressure because of the pressure drop caused by oil flowing past the orifice created by the flow compensator (margin) spool.

NOTE: Low pressure standby is not adjusted and will vary from machine to machine. It will also vary in the same pump as system or pump leakage increases. As leakage increases, the pump will upstroke slightly to compensate for the leakage, and the actuator piston will cover up more of the cross-drilled hole. As this happens, low pressure standby will drop toward margin pressure. When leakage hits the point at which the piston covers the cross-drilled hole completely, because of the increased swashplate angle required, low pressure standby will equal margin pressure.

Hydraulic Pump 4T6962/9T4833

Variable Displacement Piston Pump And Compensator Valve (4T6962)
(1) Drive shaft. (2) Swashplate. (3) Shoe plate. (4) Bias piston. (5) Piston. (6) Bias spring. (7) Compensator valve. (8) Piston shoe. (9) Cylinder barrel. (10) Actuator piston. (11) Port plate. (12) Pressure compensator spool. (13) Flow compensator spool.

This pump has two control pistons, a bias piston (4) and an actuator piston (10). The bias piston is used to upstroke the pump. It is spring (6) loaded and is assisted by pump discharge pressure. Actuator piston (10) is used to destroke the pump and has a larger area than the bias piston. The compensator valves flow compensator spool (13) and/or pressure compensator spool (12) changes pump displacement by regulating the pressure in actuator piston (10) which is supplied by discharge pressure. The larger area of actuator piston (10) enables it to overpower bias piston (4) and spring (6) to destroke the pump when compensator valve (7) applies pump discharge pressure to it. Pump outlet pressure is kept about 2070 kPa (300 psi) above work port pressure needs. The compensator valve also has a pressure limiting ability that prevents pump and system overloads. When work port pressure goes over 19 000 kPa (2750 psi), pressure compensator spool (12) will override flow compensator spool (13) and lower pump output. This action starts at about 690 kPa (100 psi) below the maximum pressure setting.

The following schematics show how the pump and its compensator valve act during different conditions in the hydraulic system.

Upstroking

Pump And Compensator Operation
(1) Spring. (2) Spring. (3) Line to control valve. (4) Actuator piston. (5) Swashplate. (6) Signal line from control valve. (7) Cavity. (8) Flow compensator spool. (9) Pressure compensator spool. (10) Passage. (11) Passage (12) Passage. (13) Passage. (14) Case drain. (15) Bias spring. (16) Bias piston.

Upstroking is when the pump is increasing displacement (output). This occurs when the signal pressure increases due to a high load (implement or steering) at low pump output. The highest resolved signal pressure (see Signal Resolver Network in Systems Operation, Backhoe Loader Hydraulics, SENR3195) goes through line (6) and fills cavity (7). Now the signal pressure, plus the force of spring (1), move spool (8) down. This blocks the flow of supply oil to actuator piston (4). With flow compensator spool (8) moved downward, oil under the actuator piston can drain past flow compensator spool (8), the pressure compensator spring cavity and out through passage (12) to case drain (14). Now supply oil flows through passage (13) to bias piston (16) and combines with the force of bias spring (15) to move swashplate toward maximum angle or UPSTROKE. This increases pump output. The pump output pressure increases until the pressure in passage (11) moves spool (8) up to the metering position. Initially, in the metering position (Figure 1), pump pressure is greater than the combined force of spring (1) and the signal pressure in cavity (7). Spool (8) moves up. Pressure is now sent to actuator piston (4). Since the area of actuator piston (4) is larger than the area of bias piston (16), the force moving swashplate (5) toward minimum angle (actuator piston) is greater than the force moving swashplate (5) toward maximum angle (bias piston plus bias spring). Swashplate (5) angle decreases. Pump output decreases. When pump pressure reduces enough the combined signal pressure and spring force in cavity (7) move spool (8) down (Figure 2). The oil pressure behind actuator piston (4) goes back to case drain per previous discussion.

Metering Position

Bias piston (16) and spring (15) force swashplate (5) angle to increase. This light up and down spool movement is called metering. Metering keeps the pressure on both ends of spool (8) equal. Spring (1) is equal to 2070 kPa (300 psi). Therefore, pump pressure is 2070 kPa (300 psi) greater than signal pressure. The difference is called margin pressure.

Destroking

Pump And Compensator Operation
(1) Spring. (2) Spring. (3) Line to control valve. (4) Actuator piston. (5) Swashplate. (6) Signal line from control valve. (7) Cavity. (8) Flow compensator spool. (9) Pressure compensator spool. (10) Passage. (11) Passage. (12) Passage. (13) Passage. (14) Case drain. (15) Bias spring. (16) Bias piston.

Destroking is when the pump is decreasing displacement (output). This occurs when the signal pressure decreases due to a low load (implement or steering) at high pump output. The lower signal pressure goes through line (6) and fills cavity (7). Now the signal pressure, plus the force of spring (1) in cavity (7), is less than the pump pressure in passage (11). Spool (8) is pushed up. Oil behind actuator piston (4) cannot go through passage (12) to case drain (14). Pump oil now flows through passage (11), past spool (8), through passage (10) and into actuator piston (4). Pump pressure behind actuator piston (4) is now greater than the combined force of bias piston (16) and spring (15). Swashplate (5) angle decreases. This decreases pump output. System pressure decreases. As system pressure approaches 2070 kPa (300 psi) margin pressure (if there is a system requirement) or 3300 kPa (480 psi) low pressure standby (if all control valves are in hold), flow compensator spool (8) moves down to the metering position. Swashplate (5) will maintain a slight angle that is sufficient to make up for system leakage and provide the lower required pressure.

Low Pressure Standby

Pump And Compensator Operation
(1) Spring. (2) Spring. (3) Line to control valve. (4) Actuator piston. (5) Swashplate. (6) Signal line from control valve. (7) Cavity. (8) Flow compensator spool. (9) Pressure compensator spool. (10) Passage. (11) Passage. (12) Passage. (13) Passage. (14) Case drain. (15) Bias spring. (16) Bias piston.

Low pressure standby is when the machine is on, the implements are in hold and steering is not being used. There are no flow or pressure demands on the pump. Therefore, there is no signal pressure in line (6).

Before the engine is started, bias spring (8) holds swashplate (9) at maximum angle. As the pump begins to turn, making oil flow, pressure builds in the system because of the closed-center implement valves. This pressure in passage (11) is felt at the bottoms of both pressure compensator (pressure limiter) and flow compensator (margin) spools. As this pressure increases, it pushes the flow compensator (margin) spool up against spring(1). When system pressure becomes greater than 2070 kPa (300 psi) spool (8) will have moved up far enough to open up a passage for pressure oil to the back of actuator piston (4). This causes the actuator piston to move to the right which compresses bias spring (15) and moves the swashplate toward minimum angle. The actuator piston continues to move to the right until it uncovers the cross-drilled passage of the actuator piston rod, allowing oil to drain to case.

At this point, pump output flow is not enough to make up for normal system leakage, the additional leakage through the cross-drilled hole, and to further increase oil pressure behind the actuator piston to continue moving it to the right. This limits the maximum travel of the piston to the right. The piston will now move slightly to the left until only part of the cross-drilled hole is open to case. At this point, the pump is producing enough flow to make up system leakage and leakage to the pump case through the cross-drilled hole while maintaining system pressure at 3300 kPa (480 psi).

The pump is at low pressure standby. This pressure is different than margin pressure because of system leakage and the cross-drilled hole in the actuator piston rod. The flow compensator (margin) spool, instead of metering oil, must remain open and move up higher against spring (1) to provide enough flow to the back side of the actuator piston to make up the leakage through the cross-drilled hole. This flow must be enough to maintain the pressure required at the back of the piston to overcome the bias spring and the pressure behind bias piston. System pressure must be approximately 1240 kPa (180 psi) higher than margin pressure to shift the spool up this additional amount against spring (1). Oil pressure behind the actuator piston is less than system pressure because of the pressure drop caused by oil flowing past the orifice created by the flow compensator (margin) spool.

NOTE: Low pressure standby is not adjusted and will vary from machine to machine. It will also vary in the same pump as system or pump leakage increases. As leakage increases, the pump will upstroke slightly to compensate for the leakage, and the actuator piston will cover up more of the cross-drilled hole. As this happens, low pressure standby will drop toward margin pressure. When leakage hits the point at which the piston covers the cross-drilled hole completely, because of the increased swashplate angle required, low pressure standby will equal margin pressure.

High Pressure Stall

Pump And Compensator Operation
(1) Spring. (2) Spring. (3) Line to control valve. (4) Actuator piston. (5) Swashplate. (6) Signal line from control valve. (7) Cavity. (8) Flow compensator spool. (9) Pressure compensator spool. (10) Passage. (11) Passage. (12) Passage. (13) Passage. (14) Case drain. (15) Bias spring. (16) Bias piston.

When the hydraulic system stalls under load or when the cylinders reach the end of the stroke, the system pressure increases. The signal pressure in line (6) and cavity (7) becomes equal to the pump output pressure. Spring (1) keeps spool (8) shifted down. When system pressure reaches 19 000 kPa (2750 psi) in passage (11), the upward force on pressure compensator spool (9) will compress spring (2), and move pressure compensator spool (9) upward. Supply oil flows through passage (10) to actuator piston (4). Pressure felt on the actuator piston will destroke the pump. Pump output (flow) decreases while system pressure is limited to 19 000 kPa (2750 psi) [zero flow and maximum pressure].

If the control lever is moved to HOLD during high pressure stall, the signal pressure in cavity (7) flows through passage (6) to the control valve where it returns to tank. System pressure begins to bleed down. At approximately 18 250 kPa (2650 psi), spring (2) moves pressure compensator spool (9) down and the system pressure in passage (11) acts against the force of spring (1) to move flow compensator spool (8) up.

Supply oil flows past flow compensator spool (8) and pressure compensator spool (9), through passage (10) to actuator piston (4). Actuator piston (4) destrokes swashplate (5) until system pressure decreases. As system pressure approaches 3300 kPa (480 psi) [low pressure standby], flow compensator spool (8) moves down to the metering position. Swashplate (5) will maintain a slight angle that is sufficient to make up for system leakage and provide the lower required pressure.

Loader Valve Group

Loader Valve Group
(1) Cover. (2) Tilt control section. (3) Lift control section. (4) Multi-purpose bucket control section (optional). (5) Inlet manifold.

The loader control valve group is located on the right frame rail in front of the rear axle. Standard equipment includes: inlet manifold with steering priority valve (5), loader lift valve (3), loader tilt valve (2) and a cover (1). Multi-purpose bucket control valve (4) is optional. This valve can also be used for other optional attachments.

Loader Valve Group
(6) Lines to HMU. (7) Supply from pump. (10) Return to tank. (13) To rod end of lift cylinder. (14) To head end of lift cylinder. (15) To rod end of tilt cylinder. (16) To head end of tilt cylinder. (17) Linkage rod to tilt lever. (18) Linkage rod to lift lever.

Linkage rods connect the valve sections to the operator control levers. The loader lever controls: loader lift, loader lower, loader float, bucket dump and bucket tilt back.

Loader Control Lever
(A) Lower. (B) Raise. (C) Tilt back. (D) Dump. (E) Neutralizer button.

The loader lever also has neutralizer button (E). When pushed, this button disengages the transmission and diverts all horsepower to the hydraulic system.

When added, the multi-purpose bucket control valve (4) has its own control lever. This lever is located next to the lift lever.

Loader Priority Inlet Manifold

Inlet Manifold
(6) Supply to HMU. (7) Supply from pump. (8) Signal to pump. (9) Signal from HMU. (10) Return to tank.

Priority inlet manifold (5) is bolted to lift control section (3) on standard valve group. The inlet manifold is bolted to multi-purpose bucket control section (4) when this option is added. There are five lines connected to the inlet manifold. Port (7) supplies oil from the pump to the inlet manifold. Port (9) receives signal oil from the HMU. Port (6) directs oil supply to the HMU. Line (8) directs the highest resolved pressure signal to the pump compensator valve. Line (10) directs return oil to tank. In addition to providing for line connections, the inlet manifold houses the steering priority valve and the final resolver which compares the HMU and loader or backhoe signal pressures.

Priority Flow To HMU

Inlet Manifold And Priority Valve (Priority Flow to HMU)
(7) Supply from pump. (9) Signal from HMU. (10) To tank. (19) Port. (20) Passage. (21) Small hole. (22) Chamber. (23) Spring. (24) Spool. (25) Passage. (26) Pressure reducing valve. (27) Spring. (28) Final resolver. (29) Passage. (30) Hole. (31) Chamber. (32) Axial passage.

The steering system has flow priority over the loader sections. When the steering wheel is turned, signal oil from the HMU is sent to the inlet manifold and priority valve port (9). This signal oil flows through port (19), then to passage (20), through hole (21) and to chamber (22). The 700 kPa (100 psi) margin spring (23) in chamber (22) combines with the HMU signal oil. The combined force moves priority valve spool (24) up. Pump oil which had been flowing from pump supply passage (7) to loader valve passage (25) is either stopped or metered by valve spool (24). Now pump oil flows from supply passage (7) into HMU supply passage (29). Then, this oil flows through the HMU supply line to the HMU. When signal oil in chamber (22) reaches 14 000 kPa (2030 psi), pressure reducing valve (26) moves down against the force of spring (27). Oil now flows into tank passage (10). The pressure in chamber (22), which has been limited to 14 000 kPa (2030 psi), is communicated to the compensator valve through final resolver (28). This limits maximum steering system pressure.

Priority Flow to Loader Section

Inlet Manifold And Priority Valve
(7) Supply from pump. (9) Signal from HMU. (10) To tank. (19) Port. (20) Passage. (21) Small hole. (22) Chamber. (23) Spring. (24) Spool. (25) Passage. (26) Pressure reducing valve. (27) Spring. (28) Final resolver. (29) Passage. (30) Hole. (31) Chamber. (32) Axial passage.

When signal pressure from the loader section exceeds the HMU signal pressure, the final resolver shifts, sending the highest resolved signal pressure (loader signal) to the compensator valve on the pump. Pump supply pressure in passage (7) increases to 1380 to 1700 kPa (200 to 245 psi) more than signal pressure. This pressure is felt in HMU supply passage (29). Pressure goes through hole (30), passage (32), to chamber (31), creating pressure on the top of the valve spool (24). This will force the spool down. Pump supply will now proceed to the loader section. This spool position also creates a restriction to limit HMU supply pressure.

Metered Flow

When no steering demand occurs there will be no signal pressure in chamber (22). Pump supply pressures is in passage (7). HMU oil enters passage (29). This oil enters spool (24) through hole (30). The oil now flows into chamber (31) through axial passage (32). Pressure in chamber (31) will force spool (24) down and allow most of the pump supply to go to passage (25). Even when there is no steering demand, there is a small leakage path to tank through the HMU. This requires that spool (24) always be in a position to maintain at least a small opening between pump supply passage (7) and HMU supply passage (29). This keeps the steering system full of oil at all times.

Loader Lift Valve 9T625

Hold Position

Loader Lift Valve (HOLD Position)
(33) Pump passage. (34) Small holes. (35) Spool. (36) Large holes. (37) Passage. 38. Springs. 39. Passage. 40. Drain passage. 41. Passage to head end of cylinder. 42. Passage to rod end of cylinder. 43. Control spool. 44. Drain passage. 45. Passage. 46. Spring. 51. Passage.

The loader valve section for lift is between the inlet manifold and the control valve section for tilt. The pump oil from the inlet section goes into passage (33). This oil goes through holes (34) into spool (35). This causes the spool to move down against the combined force of springs (38) and the pressure in signal cavity passage (51). When holes (34) start to close off passage (33), there is a restriction created which limits the pressure inside spool (35) and cavity (37) to 415 kPa (60 psi) more than the pressure in signal passage (51).

In HOLD position, the pressure in passage (51) is the same as in the hydraulic tank. Spool (43) stops pressure oil in passage (37) from going into passage (41) and passage (42). The oil in passage (42) to the rod end of the lift cylinder is blocked. The oil in passage (41) to the head end of the lift cylinder is also blocked. The loader lift arms are now held in location. The oil in passages (39), (40), (44) and (45) goes to drain.

Spring (46) holds spool (43) in this position.

Raise Position

Loader Lift Valve (RAISE Position)
(33) Pump passage. (34) Small holes. (35) Spool. (36) Large holes. (37) Passage. (38) Springs. (39) Passage. (40) Drain passage. (41) Passage to head end of cylinder. (42) Passage to rod end of cylinder. (43) Control spool. (44) Drain passage. (45) Passage. (46) Spring. (51) Passage.

In RAISE, the pressure in signal passage (51) is equal to the pressure in passage (39). Spool (43) is moved up one position. Pressure oil in passage (37) flows into passage (41). Passage (41) goes to the head end of the lift cylinder. The lift arms now raise. Oil from the rod end goes to passage (42). This oil now goes through passage (45) and passage (44) to drain. Passage (40) also drains.

Spring (46) is being compressed from the bottom in this position. When the control lever is released, spring (46) returns to normal position. This pulls the control lever back into the HOLD position.

Lower Position

Loader Lift Valve (LOWER Position)
(33) Pump passage. (34) Small holes. (35) Spool. (36) Large holes. (37) Passage. (38) Springs. (39) Passage. (40) Drain passage. (41) Passage to head end of cylinder. (42) Passage to rod end of cylinder. (43) Control spool. (44) Drain passage. (45) Passage. (46) Spring. (49) Makeup valve. (51) Passage.

In LOWER, the pressure in signal passage (51) is equal to the pressure in passage (45). Spool (43) is moved down from the HOLD position. Pressure oil flows from passage (37) into passage (42). Passage (42) goes to the rod end of the lift cylinder. The lift arms now lower. Oil from the head end leaves the cylinder. This oil enters passage (41). Oil from passage (41) goes through passage (39) and into passage (40). Passage (40) goes to tank. Passage (41) is also now connected to tank.

Spring (46) is being compressed from the top in this position. When the control lever is released, spring (46) will return to normal position. This pulls the control lever back into the HOLD position.

Float Position

Loader Lift Valve (FLOAT Position)
(33) Pump passage. (34) Small holes. (35) Spool. (36) Large holes. (37) Passage. (38) Springs. (39) Passage. (40) Drain passage. (41) Passage to head end of cylinder. (42) Passage to rod end of cylinder. (43) Control spool. (44) Drain passage. (45) Passage. (46) Spring. (47) Detent ball. (48) Pin. (49) Makeup valve. (51) Passage.

In FLOAT, the pressure in signal passage (51) is the same as in the hydraulic tank. Spool (43) is moved all the way down from the HOLD position. Spring (46) is fully compressed from the top. However, the ridge on pin (48) goes past detent balls (47). Spring (46) does not have enough force to pull pin (48) back past detent balls (47). Pin (48) is attached to spool (43). Spool (43) is now held in FLOAT position. The operator must move the control lever out of FLOAT.

In this position, pressure oil in passage (37) is blocked. This oil cannot pressurize either end of the lift cylinders. Both passages (41) and (42) are open to tank. With both cylinder ends now at the same pressure and passages (41) and (42) open to tank, the position of the lift arms is not controlled by pump oil.

In FLOAT position, the weight of the lift arms and implement will cause the implement to lower to the ground. As the machine is moved, the implement will follow the shape of the ground.

Loader Lift Valve 9T6401

Hold Position

Loader Lift Valve (HOLD Position)
(33) Pump passage. (34) Small holes. (35) Spool. (36) Large holes. (37) Passage. (38) Springs. (39) Passage. (40). Drain passage. (41). Passage to head end of cylinder. (42) Passage to rod end of cylinder. (43) Control spool. (44) Drain passage. (45) Passage. (46) Spring. (51) Passage. (A) Pump signal hole. (B) Signal hole.

The loader valve section for lift is between the inlet manifold and the control valve section for tilt. The pump oil from the inlet section goes into passage (33). This oil goes through holes (34) into spool (35). This causes the spool to move down against the combined force of springs (38) and the pressure in signal cavity passage (51). When holes (34) start to close off passage (33), there is a restriction created which limits the pressure inside spool (35) and cavity (37) to 415 kPa (60 psi) more than the pressure in signal passage (51).

In HOLD position, the pressure in passage (51) is the same as in the hydraulic tank. Spool (43) stops pressure oil in passage (37) from going into passage (41) and passage (42). The oil in passage (42) to the rod end of the lift cylinder is blocked. The oil in passage (41) to the head end of the lift cylinder is also blocked. The loader lift arms are now held in location. The oil in passages (39), (40), (44) and (45) goes to drain.

Spring (46) holds spool (43) in this position.

Raise Position

Loader Lift Valve (RAISE Position)
(33) Pump passage. (34) Small holes. (35) Spool. (36) Large holes. (37) Passage. (38) Springs. (39) Passage. (40) Drain passage. (41) Passage to head end of cylinder. (42) Passage to rod end of cylinder. (43) Control spool. (44) Drain passage. (45) Passage. (46) Spring. (51) Passage. (A) Pump signal hole. (B) Signal hole.

In the RAISE position, spool (43) is moved up. As the spool starts to move, hole (A) gets pump oil and sends it through hole (B). The oil goes to signal passage (39) and causes the pump to upstroke. Basically, this advanced signal causes the pump to increase output. Then, when spool (43) moves up far enough, pump oil from passage (37) goes into work port (41). The pressure is now high enough to prevent the loader frame from drooping before continuing to raise. Some of the oil in port (41) now goes to signal passage (39). This oil goes from the resolver network to the pump. The pump adjusts as required by the actual load. Oil from the rod end of the cylinder is forced out. This oil goes through port (42), around spool (43), to signal passage (45) and then to tank passage (44). In the RAISE position, pressure in passage (51) is equal to the pressure in passage (39). Pressure in passage (51) is greater than the pressure in passage (44).

Lower Position

Loader Lift Valve (LOWER Position)
(33) Pump passage. (34) Small holes. (35) Spool. (36) Large holes. (37) Passage. (38) Springs. (39) Passage. (40) Drain passage. (41) Passage to head end of cylinder. (42) Passage to rod end of cylinder. (43) Control spool. (44) Drain passage. (45) Passage. (46) Spring. (49) Makeup valve. (51) Passage. (A) Pump signal hole. (B) Signal hole.

In LOWER, the pressure in signal passage (51) is equal to the pressure in passage (45). Spool (43) is moved down from the HOLD position. Pressure oil flows from passage (37) into passage (42). Passage (42) goes to the rod end of the lift cylinder. The lift arms now lower. Oil from the head end leaves the cylinder. This oil enters passage (41). Oil from passage (41) goes through passage (39) and into passage (40). Passage (40) goes to tank. Passage (41) is also now connected to tank.

Spring (46) is being compressed from the top in this position. When the control lever is released, spring (46) will return to normal position. This pulls the control lever back into the HOLD position.

Float Position

Loader Lift Valve (FLOAT Position)
(33) Pump passage. (34) Small holes. (35) Spool. (36) Large holes. (37) Passage. (38) Springs. (39) Passage. (40) Drain passage. (41) Passage to head end of cylinder. (42) Passage to rod end of cylinder. (43) Control spool. (44) Drain passage. (45) Passage. (46) Spring. (47) Detent ball. (48) Pin. (49) Makeup valve. (51) Passage. (A) Pump signal hole. (B) Signal hole.

In FLOAT, the pressure in signal passage (51) is the same as in the hydraulic tank. Spool (43) is moved all the way down from the HOLD position. Spring (46) is fully compressed from the top. However, the ridge on pin (48) goes past detent balls (47). Spring (46) does not have enough force to pull pin (48) back past detent balls (47). Pin (48) is attached to spool (43). Spool (43) is now held in FLOAT position. The operator must move the control lever out of FLOAT.

In this position, pressure oil in passage (37) is blocked. This oil cannot pressurize either end of the lift cylinders. Both passages (41) and (42) are open to tank. With both cylinder ends now at the same pressure and passages (41) and (42) open to tank, the position of the lift arms is not controlled by pump oil.

In FLOAT position, the weight of the lift arms and implement will cause the implement to lower to the ground. As the machine is moved, the implement will follow the shape of the ground.

Makeup Valve

Makeup Valve
(42) Passage to lift cylinder rod end. (44) Drain passage. (49) Makeup valve. (50) Spring.

When the flow of oil to the rod ends of the cylinders is not enough, the pressure of the oil in passage (42) is low. The higher pressure of the oil in the passage to the tank opens the valve and lets more oil go to the rod ends of the cylinders.

Makeup valve (49) is in the control valve section for lift. The makeup valve is in passage (42) to the rod ends of the lift cylinders.

Spring (50) and oil pressure in the spring chamber hold the valve closed. The valve opens only when the flow of pump oil to the rod ends of the lift cylinders is not enough and when the control valve spool is in either the FLOAT or LOWER position.

Loader Tilt Valve

Hold Position

Loader Tilt Valve (Hold Position)
(1) Line relief and makeup valve. (2) Port to head end of cylinder. (3) Port to rod end of cylinder. (4) Control spool. (5) Passage to tank. (6) Signal passage. (7) Spool. (8) Holes. (9) Pump passage. (10) Passage. (11) Spring. (12) Signal cavity. (13) Signal port. (14) Signal passage. (15) Passage to tank. (16) Spring. (17) Magnetic detent. (18) Control spool signal passage. (A), (B) Cross drilled holes.

The location of the control valve section for the loader tilt valve is between the end cover and the control valve section for lift. This valve section has a "return to dig" or bucket positioning feature. This features is controlled by magnetic detent (17). When the bucket is in a DUMP position (generally when bucket cutting edge is lower than the bucket heel), a switch on the lift arm closes. This energizes magnetic detent (17). Then, when the operator pulls the tilt control lever to the maximum TILT BACK position and releases it, the magnetic detent will hold control spool (4) at full TILT BACK until the bucket returns to the DIG position. When the bucket returns to the level position, the electrical switch opens and de-energizes detent (17). Now spring (16) returns to its normal (not compressed) position. This pulls the control lever into HOLD and the bucket stays in the level position. The operator will use this feature after dumping a load. This feature allows the operator to move his hand from the TILT controls to the LOWER controls while the bucket continues to level automatically. The operator can, at any time, pull valve spool (4) out of the detented position by pushing the control lever toward the HOLD position.

Pump oil enters through passage (9). This passage is common in all valve sections and has no outlet. Pump oil goes through holes (8) into spool (7). Spool (7) now moves down against the combined signal pressure from port (13) and the force of spring (11) in cavity (12). When holes (8) begin to close off pump passage (9), a restriction is created. This limits pressure inside spool (7) to 415 kPa (60 psi) more than the pressure in signal cavity (12). The pressure inside spool (7) is the same as the pressure in passage (10).

In HOLD position, the pressure in passage (13) is the same as in the hydraulic tank. Spool (4) stops the flow of pressure oil from going to ports (2) and (3). The oil in port (2) to the head end of the cylinder is blocked. The oil in port (3) to the rod end of the cylinder is blocked. The bucket is now held in position. The oil in passages (5), (6), (14) and (15) goes to tank. Spring (16) holds spool (4) in this position.

Dump Position

Loader Tilt Valve (DUMP Position)
(1) Line relief and makeup valve. (2) Port to head end of cylinder. (3) Port to rod end of cylinder. (4) Control spool. (5) Passage to tank. (6) Signal passage. (10) Passage. (12) Signal cavity. (14) Signal passage. (15) Passage to tank. (18) Control spool signal passage.

In the DUMP position, spool (4) is moved down. Oil from passage (10) now goes around the spool and into passage (3). Most of this oil goes to the rod end of the cylinder. The bucket dumps. Some of the oil from passage (3) goes through passage (6) and on to the resolver network. This oil adjusts the pump as required by the load. The oil from the rod end is forced out the cylinder through passage (2). The oil goes around spool (4), to signal passage (14) and then tank passage (15). In the DUMP position, pressure in cavity (12) is equal to the pressure in passage (6). The pressure in cavity (12) is greater than the pressure in passage (14). See LINE RELIEF VALVE AND MAKEUP VALVE for the operation of valve (1).

Tiltback Position

Loader Tilt Valve (TILT BACK Position)
(1) Line relief and makeup valve. (2) Port to head end of cylinder. (3) Port to rod end of cylinder. (4) Control spool. (5) Passage to tank. (6) Signal passage. (10) Passage. (12) Signal cavity. (14) Signal passage. (15) Passage to tank. (18) Control spool signal passage.

In the TILT BACK position, spool (4) is moved up. As the spool starts to move, hole (A) gets pump oil and sends it through hole (B). The oil goes to signal passage (14) and causes the pump to upstroke. Basically, this advanced signal causes the pump to increase output. Then, when spool (4) moves up far enough, pump oil from passage (10) goes into work port (2). The pressure is now high enough to prevent the bucket from drooping when going from partial TILT BACK to full TILT BACK. Some of the oil in port (2) now goes to signal passage (14). This oil goes from the resolver network to the pump. The pump adjusts as required by the actual load. Oil from the head end of the cylinder is forced out. This oil goes through port (3), around spool (4), to signal passage (6) and then to tank passage (5). In the TILT BACK position, pressure in passage (12) is equal to the pressure in passage (14). Pressure in cavity (12) is greater than the pressure in passage (6).

Line Relief and Makeup Valve (Pilot Operated)

Valve Cross Section
(1) Passage to spring chamber. (2) Valve. (3) Spring. (4) Passage to tank. (5) Pilot valve. (6) Spring. (7) Screw. (8) Locknut.

The relief valve is a pilot-type valve. Work port oil flows through passage (1) into the spring chamber. This pressure and spring (3) hold valve (2) closed. The pressure of the oil is also against pilot valve (5) which is held closed by spring (6).

When the oil in spring (3) chamber has more pressure than the force of spring (6), valve (5) will open (move right). The oil in spring (3) chamber now goes past open pilot valve (5). This oil goes through passage (4) to the tank, faster than the oil which comes through passage (1). With only the force of spring (3) on valve (2), the pressure of the work port oil against valve (2) opens it and the work port oil goes to the tank. The open relief valve keeps the pressure of the work port oil from going higher than the setting of the relief valve.

The relief valve is also a makeup valve. Often the pressure of the pump oil to the cylinder(s) is less than the pressure of the return oil from the cylinder(s). Therefore, the oil pressure in spring (3) chamber is also less than the return oil. When the pressure of the return oil has more force on valve (2) than spring (3) has on the valve, the valve opens (moves right). The return oil now goes past valve (2) into the pump oil. The pressure of the pump oil and the return oil becomes the same.

If the relief valve setting needs an adjustment, screw (7) is turned in the direction needed to get either a pressure decrease or pressure increase. Locknut (8) is used to keep screw (7) from turning after the adjustment is made.

Multi-Purpose Bucket Valve (Option)

Hold Position

Hold Position
(1) Line relief and makeup valve. (2) Port to head end of cylinder. (3) Port to rod end of cylinder. (4) Control spool. (5) Passage to tank. (6) Signal passage. (7) Spool. (8) Holes. (9) Pump passage. (10) Passage. (11) Spring. (12) Signal cavity. (13) Signal port. (14) Signal passage. (15) Passage to tank. (16) Spring.

If the machine is ordered with the optional multi-purpose bucket and valve system, the valve is located between the valve section for lift and the inlet manifold.

Pump oil enters through passage (9). This passage is common in all valve sections and has no outlet. Pump oil goes through holes (8) into spool (7). Spool (7) now moves down against the combined signal pressure from port (13) and the force of spring (11) in cavity (12). When holes (8) begin to close off pump passage (9), a restriction is created. This limits pressure inside spool (7) to 415 kPa (60 psi) more than the pressure in signal cavity (12). The pressure inside spool (7) is the same as the pressure in passage (10).

In the HOLD position, spool (4) stops the pressure oil in passage (10) from going into port (2) and port (3). The oil in port (2) to the head end is blocked. The oil in port (3) to the rod end is also blocked. The oil in passages (5), (6), (14) and (13) goes to tank.

Open Position

In the OPEN position, spool (4) is moved down. Oil from passage (10) goes around spool (4) and into port (3). Most of this oil goes to the rod end of the cylinder. The bucket clam opens. Some of the oil in port (3) goes through passage (6) to the resolver network. If this oil is the highest resolved pressure in the network, it will go to the compensator valve and be used to adjust the pump as required by the load. The oil from the head end of the cylinder is forced out of the cylinder through port (2). This oil now goes past spool (4) to signal passage (14) and then to tank through passage (15). In OPEN, pressure in cavity (12) is equal to the pressure in passage (6) and greater than the pressure in passage (14). Spring (16) will return spool (4) to the HOLD position when the control lever is released. See LINE RELIEF AND MAKEUP VALVE for the operation of valve (1).

Multi-Purpose Bucket Valve (OPEN Position)
(1) Line relief and makeup valve. (2) Port to head end of cylinder. (3) Port to rod end of cylinder. (4) Control spool. (5) Passage to tank. (6) Signal passage. (10) Passage. (12) Signal cavity. (14) Signal passage. (15) Passage to tank. (16) Spring.

Closed Position

Multi-Purpose Bucket Valve (CLOSED Position)
(1) Line relief and makeup valve. (2) Port to head end of cylinder. (3) Port to rod end of cylinder. (4) Control spool. (5) Passage to tank. (6) Signal passage. (10) Passage. (12) Signal cavity. (14) Signal passage. (15) Passage to tank. (16) Spring.

In the CLOSED position, spool (4) moves up. Oil from passage (10) goes around spool (4) and into port (2). Most of this oil goes to the head end of the cylinder. The bucket clam closes. Some of the oil in port (3) goes through passage (14) to the resolver network. If the oil is the highest resolved pressure in the network, it will go the compensator valve. This oil will then be used to adjust the pump as required by load.

The oil from the rod end of the cylinder is forced out of the cylinder through port (3). This oil now goes past spool (4) to signal passage (6) and also to tank through passage (5). In CLOSE, pressure in cavity (12) is equal to the pressure in passage (14) and greater than the pressure in passage (6). Spring (16) will return spool (4) to the HOLD position when the control lever is released.

Backhoe Valve Group

Backhoe Valve Sections
(1) Cover. (2) Auxiliary (option). (3) Left stabilizer. (4) Boom. (5) Swing. (6) Bucket. (7) Stick. (8) Right stabilizer. (9) Auxiliary (option) (extendable stick). (10) Inlet manifold and return restrictor. (11) Inlet port. (12) Drain port.

The backhoe control valve group is located below the floor plate at the rear of the operator station. It bolts to a bracket in four places. The bracket is mounted on the inside of the rear frame cross member. Standard equipment includes: inlet manifold and return restrictor valve (10), right stabilizer valve sections (8), stick valve section (7), bucket valve section (6), swing valve section (5), boom valve section (4), left stabilizer valve section (3) and cover (2).

Optional auxiliary valve sections are available. They include: extendable stick valve section (9) and an auxiliary control valve section (2). These two auxiliary valve sections may have other uses. Linkage rods connect all valve sections to the operator control levers. All control valve sections are all closed centered.

Inlet Manifold and Return Oil Restrictor

Inlet manifold (1) is bolted to the right stabilizer section (8) on standard groups. The manifold is bolted to the auxiliary extendable stick valve section (9) when this option is added. There are three lines connected to the manifold.

Backhoe Valve Group
(11) Inlet line from pump. (12) Outlet line to tank. (13) Signal line from backhoe resolver network.

Line (11) supplies oil from the pump. Line (12) directs return oil to tank. Line (13) directs the highest backhoe load signal to the loader control valve.

In addition to providing for line connections, this manifold houses a return restrictor valve.

When any backhoe circuit is operated at high pressure, the signal oil enters port (17) and goes to passage (18). This pressure causes spool (19) to act against the force of spring (20). The spool shifts down. This allows oil returning from the backhoe circuits in chamber (22) to go around spool (19) and into passage (21). This passage connects to return line (12). Backhoe return oil now continues to tank.

Inlet Manifold And Return Restrictor (OPEN Position)
(17) Signal inlet port. (18) Passage. (19) Spool. (20) Spring. (21) Passage to return line. (22) Return chamber. (23) Supply passage.

Inlet Manifold And Return Restrictor (CLOSED Position)
(17) Signal inlet port. (18) Passage. (19) Spool. (20) Spring. (21) Passage to return line. (22) Return chamber. (23) Supply passage.

During overrunning load conditions (e.g., dropping the boom quickly) the weight of the implement causes a high return flow rate. The resolved signal at the work ports is low. Since the signal is low, spring (20) now pushes spool (19) up. This restricts the backhoe circuit return oil from going to passage (21) and to tank. Pressure now builds up inside return chamber (22). This is also felt in all of the backhoe valve sections. This back pressure forces oil through the makeup and relief valves into the work ports. Cavitation is prevented. In overrunning load conditions in the backhoe, the restrictor spool restricts flow to tank and forces the makeup valve to redirect the return oil to the work ports.

Backhoe Auxiliary Valve Sections (Options)

This machine can be equipped with two backhoe auxiliary valves. One of these optional valves can be located between the inlet manifold and the right stabilizer valve section. Generally, this optional valve section is intended to be for the extendable stick or a hammer. The other optional valve is located between the left stabilizer and the end cover. This valve is intended to control an attachment like a clam added to the extendable stick. Both auxiliary valves are identical.

Auxiliary Valve
(1) Work ports. (2) Control spool. (3) Drain passage. (4) Signal passage. (5) Compensator spool. (6) Pump passage. (7) Passage. (8) Springs. (9) Signal cavity. (10) Signal port. (11) Signal passage. (12) Drain passage. (13). Spring.

These valves contain only pressure compensation valve (5) and main control spool (2). There are only three spool positions. Hold is in the middle. Spring (13) provides a return to Hold feature for both of the other spool positions. For the extendable stick option, pulling up on spool (2) pressurizes the rod end of the cylinder. This retracts the extendable stick. No relief or makeup valves are provided. Flow is limited to 91 liter/min (24 U.S. gpm).

Stabilizer Valves

HOLD Position
(1) Spool. (2) Drain passage. (3) Signal passage. (4) Passage. (5) Supply port. (6) Passage. (7) Cavity. (8) Signal passage. (9) Drain passage. (10) Spring. (11) Cavity. (12) Spring. (13) Valve. (14) Lock valve. (15) Line to head end. (16) Line to rod end. (21) Cavity. (22) Passage.

The location of the left stabilizer valve section, on a standard valve group, is between the end cover and the boom control valve. The control valve for the right stabilizer is between the inlet manifold and the stick control valve. Both valves are the same.

NOTE: The terms right and left shall be determined by the position of the operator when seated in either the loader operating position or the backhoe operating position.

LOWER Position
(1) Control valve spool. (2) Drain port. (3) Signal passage. (4) Passage to rod end. (5) Pump port. 6. Passage. (7) Cavity. (8) Signal port and passage to head end. (9) Drain passage. (10) Spring. (11) Cavity. (12) Spring. (13) Valve. (14) Lock valve. (15) Line to head end. (16) Line to rod end. (17) Stabilizer. (18) Head end of cylinder. (19) Rod end of cylinder. (20) Orifice check valve. (21) Cavity. (22) Passage.

The stabilizer valve sections do not have line relief and makeup valves. Lock valve (14) is in the head end control valve port. Lock valve (14) minimizes leakage through the valve. This prevents cylinder drift. This valve also stops vehicle droop when the vehicle is raised from a partially raised position. It also gives uniform lower rates when both stabilizers are lowered at the same time.

The stabilizer valve sections do not have a compensator valve. Flow is limited to 75 liter/min. (20 U.S. gpm). In HOLD position, spring (10) centers spool (1). Pump oil enters port (5) and fills cavity (7) and passage (6). In this position, spool (1) blocks oil flow to passage (4) and passage (8). The oil in cavity (11), passage (22) and passage (23) goes through signal passage (8) and then to drain passage (9). Spring (12) pulls valve (13) to the right. When seated, valve (13) blocks the oil from the cylinder head end from going to drain. The stabilizer is now held in position. Since valve leakage is prevented by seated valve (13), the stabilizer will not droop in HOLD position.

Lowering stabilizer (17) raises the machine. To lower stabilizer (17), control spool (1) is moved up. This compresses spring (10). This also lets the pump oil from passage (5), cavity (7) and passage (6) go past spool (1) and into cavity (11). Pump oil also goes through passage (22) into cavity (21). The oil in cavity (21) and (11) moves valve (13) left against the force of spring (12). Pump oil now goes through line (15) and orifice (20) to stabilizer cylinder head end (18). Control spool (1) blocks pump oil in passage (8) from going to drain through passage (9). Spool (1) also blocks pump oil in passage (6) from going to passage (4). The oil being forced out of the stabilizer cylinder rod end (19) goes through line (16), unseats orifice check valve (20) and enters passage (4). This oil now goes through signal passage (3) to drain passage (2).

When the operator lets go of the control spool lever, spring (10) moves spool (1) to the HOLD position.

RAISE Position
(1) Control valve spool. (2) Drain passage. (3) Signal passage. (4) Passage to rod end. (5) Pump port. (6) Passage. (7) Cavity. (8) Signal port and passage to head end. (9) Drain passage. (10) Spring. (11) Cavity. (12) Spring. (13) Valve. (14) Lock valve. (15) Line to head end. (16) Line to rod end. (17) Stabilizer. (18) Head end of cylinder. (19) Rod end of cylinder. (20) Orifice check valve. (21) Cavity. (22) Passage.

Raising stabilizers (17) lowers the machine. To raise the stabilizer, control spool (1) is moved down. This compresses spring (10). This also lets pump oil from passage (5), cavity (7) and passage (6) go past spool (1) and into passage (4). Some oil goes to signal passage (3). Some of the pump oil in passage (6) also goes into passage (22) and cavity (21). This forces valve (13) left against the force of spring (12). The oil in passage (4) goes through orifice (20). This oil goes through line (16) to rod end (19). Oil being forced out of head end (18) now goes through orifice (20). This oil goes through line (15) to lock valve (14). Now the oil goes past unseated valve (13). This oil goes through cavity (11) to drain passage (9). The purpose of head end orifice (20) is to control the rate of vehicle drop until it reaches the ground when raising the stabilizer. The purpose of rod end orifice (20) is to keep pump pressure high enough so lock valve (14) stays open (left) when raising stabilizers (17) at low idle. This prevents instability which would occur if lock valve (14) were allowed to open and close during overrunning load condition. When the operator lets go of the control spool lever, spring (10) moves spool (1) to the HOLD position. Pump oil is blocked. It cannot go to passage (4) or passage (8). The oil in cavity (21) and passage (22) drains. Spring (12) moves valve (13) right. Now, all oil inside the stabilizer is blocked. The stabilizers stay in this position until the operator moves the control lever.

Stick Valve 9T628

Hold Position

Stick Valve (HOLD Position)
(1) Makeup and relief valve. (2) Port to head end of cylinder. (3) Port to rod end of cylinder. (4) Control spool. (5) Passage to tank. (6) Signal passage. (7) Spool. (8) Holes. (9) Pump passage. (10) Passage. (11) Spring. (12) Signal cavity. (13) Signal port. (14) Signal passage. (15) Passage to tank. (16) Spring. (17) Control spool signal passages. (A), (B) Cross drilled holes.

The location of the control valve section for the backhoe stick is between the control valve section for bucket and the control valve section for the right stabilizer.

Spring (16) on the end of valve spool (4) is compressed when the spool is moved to either the IN or OUT position. The spring will move valve spool (4) and the control lever to HOLD when the lever is released.

Pump oil from the valve section for the right stabilizer enters the stick valve section through passage (9). Passage (9) is a common passage through all of the valve sections. Passage (9) has no outlet. The pump oil goes through holes (8) into spool (7). This causes the spool to move down against the combined signal pressure from port (13) and the force of spring (11) in cavity (12). When holes (8) begin to close off pump passages (9), there is a restriction created which limits pressure inside spool (7) to 415 kPa (60 psi) greater than the pressure in signal cavity (12). The pressure inside spool (7) is the same as the pressure in passage (10).

In HOLD position, spool (4) stops pressure oil in passage (10) from going into ports (2) and (3). The oil in port (3) to the rod end of the stick cylinder is blocked. The oil in port (2) to the head end of the stick cylinder is also blocked. The stick is now held in location. The oil in passages (12), (5), (6), (14) and (15) goes to drain.

Spring (16) now holds spool (4) in this position.

Out Position

Stick Valve (OUT Position)
(2) Port to head end of cylinder. (3) Port to rod end of cylinder. (4) Control spool. (5) Passage to tank. (6) Signal passage. (10) Passage. (12) Signal cavity. (14) Signal passage. (15) Passage to tank. (16) Spring. (17) Control spool signal passages. (A), (B) Cross drilled holes.

In the OUT position, spool (4) is moved down. As the spool starts to move, hole (A) gets pump oil and sends it through hole (B). This oil goes to signal passage (6) and causes the pump to upstroke. Then, when the spool moves down far enough, pump oil from passage (10) goes past spool (4) into port (3). The pump oil pressure is now high enough to prevent stick droop. Oil in port (3) goes to the rod end of the cylinder. Some of the oil in port (3) goes to the resolver network through passage (6) to adjust pump output to the actual required level. Oil being forced out of the head end enters passage (2). This oil now goes past spool (4), through passage (14) and (15), to tank. In the OUT position, pressure in passage (12) is equal to the pressure in passage (6). Spring (16) is compressed from the top in the OUT positions. When the operator releases the stick lever, spring (16) moves the lever and spool (4) into HOLD. See LINE RELIEF AND MAKEUP VALVE for the operation of valve (1).

In Position

Stick Valve (IN Position)
(2) Port to head end of cylinder. (3) Port to rod end of cylinder. (4) Control spool. (5) Passage to tank. (6) Signal passage. (10) Passage. (12) Signal cavity. (14) Signal passage. (15) Passage to tank. (16) Spring. (17) Control spool signal passages. (A), (B) Cross drilled holes.

In the IN position, spool (4) is moved up. Holes (A) and (B) are not a factor. Pump oil from passage (10) goes past spool (4) into port (2). Most of this oil goes to the head end of the cylinder. This extends the cylinder and pulls the stick in (down). Some of the oil from passage (2) goes to signal passage (14). The oil that is forced out of the rod end of the cylinder goes through port (3) and passage (6) to drain (5). In the IN position, pressure in passage (12) is equal to the pressure in passage (14). Spring (16) is compressed from the bottom in the IN position. When the operator releases the stick lever, spring (16) moves the lever and spool (4) into HOLD. See LINE RELIEF AND MAKEUP VALVE for the operation of valve (1).

Stick Valve 9T7170

Hold Position

Stick Valve (HOLD Position)
(1) Makeup and relief valve. (2) Port to head end of cylinder. (3) Port to rod end of cylinder. (4) Control spool. (5) Passage to tank. (6) Signal passage. (7) Spring. (8) Check valve. (9) Spool. (10) Passage. (11) Passage. (12) Passage. (13) Springs. (14) Signal passage. (15) Signal passage. (16) Passage to tank. (17) Spring. (A) Signal hole. (B) Pump signal hole.

The location of the control valve section for the backhoe stick is between the control valve section for bucket and the control valve section for the right stabilizer.

Spring (17) on the end of valve spool (4) is compressed when the spool is moved to either the IN or OUT position. The spring will move valve spool (4) and the control lever to HOLD when the lever is released.

Pump oil from the valve section for the right stabilizer enters the stick valve section through passage (10). This passage is common through all of the valve sections. Passage (10) has no outlet. At first, pump oil can only get into small passage (11) between load check valve (8) and compensator spool (9). Pump pressure continues to build. When the pressure is high enough, load check valve (8) is moved up against the force of spring (7). This higher than normal pressure now fills the area between load check valve (8) and compensator spool (9). This causes compensator spool (9) to move down against the combined signal pressure from port (15) and the force of spring (13) in passage (14). When compensator spool (9) moves down far enough, the small holes in the spool begin to close off pump passage (10). A restriction is created. Pressure inside spool (9) is 415 kPa (60 psi) greater than the pressure in signal passage (14). The pressure inside spool (9) is the same as the pressure in passage (10). This oil now can flow through compensator spool (9) into passage (12).

In HOLD position, spool (4) stops pressure oil in passage (10) from going into ports (2) and (3). The oil in port (3) to the rod end of the stick cylinder is blocked. The oil in port (2) to the head end of the stick cylinder is also blocked. The stick is now held in location. The oil in passages (5), (6), (14), (15) and (16) goes to drain.

Spring (17) now holds spool (4) in this position.

Out Position

Stick Valve (OUT Position)
(1) Makeup and relief valve. (2) Port to head end of cylinder. (3) Port to rod end of cylinder. (4) Control spool. (5) Passage to tank. (6) Signal passage. (7) Spring. (8) Check valve. (9) Spool. (10) Passage. (11) Passage. (12) Passage. (13) Springs. (14) Signal passage. (15) Signal passage. (16) Passage to tank. (17) Spring. (A) Signal hole. (B) Pump signal hole.

In the OUT position, spool (4) is moved down. As the spool starts to move, hole (B) gets pump oil and sends it through hole (A). This oil goes to signal passage (6) and causes the pump to upstroke. Then, when the spool moves down far enough, pump oil from passage (10) goes past spool (4) into port (3). The pump oil pressure is now high enough to prevent stick droop. Oil in port (3) goes to the rod end of the cylinder. Some of the oil in port (3) goes to the resolver network through passage (6) to adjust pump output to the actual required level. Oil being forced out of the head end enters passage (2). This oil now goes past spool (4), through passage (15) and (16), to tank. In the OUT position, pressure in passage (14) is equal to the pressure in passage (6). Spring (17) is compressed from the top in the OUT positions. When the operator releases the stick lever, spring (17) moves the lever and spool (4) into HOLD. See LINE RELIEF AND MAKEUP VALVE for the operation of valve (1).

In Position

Stick Valve (IN Position)
(1) Makeup and relief valve. (2) Port to head end of cylinder. (3) Port to rod end of cylinder. (4) Control spool. (5) Passage to tank. (6) Signal passage. (7) Spring. (8) Check valve. (9) Spool. (10) Passage. (11) Passage. (12) Passage. (13) Springs. (14) Signal passage. (15) Signal passage. (16) Passage to tank. (17) Spring. (A) Signal hole. (B) Pump signal hole.

In the IN position, spool (4) is moved up. Holes (A) and (B) are not a factor. Pump oil from passage (10) goes past spool (4) into port (2). Most of this oil goes to the head end of the cylinder. This extends the cylinder and pulls the stick in (down). Some of the oil from passage (2) goes to signal passage (15). The oil that is forced out of the rod end of the cylinder goes through port (3) and passage (6) to drain (5). In the IN position, pressure in passage (14) is equal to the pressure in passage (15). Spring (17) is compressed from the bottom in the IN position. When the operator releases the stick lever, spring (17) moves the lever and spool (4) into HOLD. See LINE RELIEF AND MAKEUP VALVE for the operation of valve (1).

Stick Valve 9T7935

Hold Position

Stick Valve (HOLD Position)
(1) Line makeup and relief valve. (2) Port to head end. (3) Port to rod end. (4) Control spool. (5) Passage to tank. (6) Signal passage. (7) Spring. (8) Load check valve. (9) Compensator spool. (10) Pump passage. (11) Passage. (12) Passage. (13) Springs. (14) Signal passage. (15) Signal passage. (16) Passage to tank. (17) Spring. (A) Signal hole. (B) Pump signal hole. (C) Pump signal hole. (D) Signal hole.

The location of the control valve for the backhoe stick is between the control valve sections for the bucket and for the right stabilizer.

Spring (17) on the end of valve spool (4) is compressed when the spool is moved to either the IN or OUT position. The spring will move valve spool (4) and the control lever to HOLD when the lever is released.

Pump oil from the valve section for the right stabilizer enters the stick valve section through passage (10). This passage is common through all of the valve sections. Passage (10) has no outlet. At first, pump oil can only get into small passage (11) between load check valve (8) and compensator spool (9). Pump pressure continues to build. When the pressure is high enough, load check valve (8) is moved up against the force of spring (7). This higher than normal pressure now fills the area between load check valve (8) and compensator spool (9). This causes compensator spool (9) to move down against the combined signal pressure from port (15) and the force of spring (13) in passage (14). When compensator spool (9) moves down far enough, the small holes in the spool begin to close off pump passage (10). A restriction is created. Pressure inside spool (9) is 415 kPa (60 psi) greater than the pressure in signal passage (14). The pressure inside spool (9) is the same as the pressure in passage (10). This oil now can flow through compensator spool (9) into passage (12).

In HOLD position, control spool (4) stops pressure oil in passage (12) from going to ports (2) and (3). The oil in port (2) to the head end of the stick cylinder is blocked. The oil in port (3) to the rod end is also blocked. The stick is now held in location. The oil in passages (5), (6), (15) and (16) goes to drain.

Spring (17) now holds control spool (4) in this position.

Out Position

Stick Valve Section (OUT Position)
(1) Line makeup and relief valve. (2) Port to head end. (3) Port to rod end. (4) Control spool. (5) Passage to tank. (6) Signal passage. (7) Spring. (8) Load check valve. (9) Compensator spool. (10) Pump passage. (11) Passage. (12) Passage. (13) Springs. (14) Signal passage. (15) Signal passage. (16) Passage to tank. (17) Spring. (A) Signal hole. (B) Pump signal hole. (C) Pump signal hole. (D) Signal hole.

In the OUT position, spool (4) is moved down. As the spool starts to move, hole (B) gets pump oil and sends it through hole (B). This oil goes to signal passage (6) and causes the pump to upstroke. Then, when the spool moves down far enough, pump oil from passage (10) goes past spool (4) into port (3). The pump oil pressure is now high enough to prevent stick droop. Oil from passage (12) now goes around spool (4) to port (3). Most of this oil goes to the rod end of the stick cylinder. The stick cylinder extends and the stick goes out. Some of the oil from port (3) goes to signal passage (6). The oil goes to the resolver network to adjust the pump as required by the load. The oil from the head end of the stick cylinder is forced out. This oil enters port (2). The oil goes past spool (4) to signal passage (15). Finally, this oil goes through passage (16) to tank. In the OUT position, pressure in passage (14) is the same as the pressure in passage (6). Spring (17) is compressed from the top. When the control lever is released, spring (17) moves spool (4) into the HOLD position.

In Position

Stick Valve Section (IN Position)
(1) Line makeup and relief valve. (2) Port to head end. (3) Port to rod end. (4) Control spool. (5) Passage to tank. (6) Signal passage. (7) Spring. (8) Load check valve. (9) Compensator spool. (10) Pump passage. (11) Passage. (12) Passage. (13) Springs. (14) Signal passage. (15) Signal passage. (16) Passage to tank. (17) Spring. (A) Signal hole. (B) Pump signal hole. (C) Pump signal hole. (D) Signal hole.

In the IN position, spool (4) is moved up. As the spool starts to move, hole (C) gets pump oil. This oil goes through hole (D) to signal passage (15). This advanced signal causes the pump to upstroke. As the spool moves farther up, high pressure oil goes past spool (4) to port (2). This oil has a high enough pressure to prevent stick droop. The oil goes to the head end of the stick cylinder. The cylinder retracts. The stick moves in. Some of the oil from port (2) goes to passage (15). The oil now goes to the resolver network to adjust the pump output as required by the actual load. Oil from the rod end of the cylinder is forced out. This oil enters port (3). The oil goes past spool (4) to signal passage (6). Finally, this oil goes through passage (5) to tank. In the IN position, pressure in passage (14) is the same as the pressure in passage (15). Spring (17) is compressed from the bottom. When the control lever is releases, spring (17) moves spool (4) into the HOLD position.

Bucket Valve 9T630

Hold Position

Bucket Valve (HOLD Position)
(1) Makeup and relief valve. (2) Port to rod end of cylinder. (3) Port to head end of cylinder. (4) Main control spool. (5) Passages to tank. (6) Signal passages to primary resolver. (7) Spool. (8) Holes. (9) Pump passage. (10) Passage. (11) Spring. (12) Signal cavity. (13) Signal port. (14) Signal passage to primary resolver. (15) Passage to tank. (16) Spring.

The location of the control valve section for the backhoe bucket is between the control valve section for swing and the control valve section for stick.

Spring (16) on the end of valve spool (4) is compressed when the spool is moved to either the DUMP or LOAD position. The spring will move valve spool (4) and the control lever to HOLD when the lever is released.

Pump oil from the valve section for stick enters the bucket valve section through passage (9). Passage (9) is a common passage through all of the valve sections. Passage (9) has no outlet. The pump oil goes through holes (8) into spool (7). This causes the spool to move down against the combined signal pressure from port (13) and the force of spring (11) in cavity (12). When holes (8) begin to close off pump passage (9), there is a restriction created which limits pressure inside spool (7) to 415 kPa (60 psi) greater than the pressure in signal cavity (12). The pressure inside spool (7) is the same as the pressure in passage (10).

In HOLD position, spool (4) stops pressure oil in passage (10) from going into port (2) and (3). The oil in port (3) to the head end of the bucket cylinder is blocked. The oil in port (2) to the rod end of the bucket cylinder is also blocked. The bucket is now held in location. The oil in passage (5), (6), (12), (14) and (15) goes to drain.

Spring (16) now holds spool (4) in this position.

Load Position

Bucket Valve (LOAD Position)
(2) Port to rod end of cylinder. (3) Port to head end. (4) Control spool. (5) Passage to tank. (6) Signal passage. (10) Passage. (12) Signal cavity. (14) Signal passage. (15) Passage to tank. (16) Spring.

In the LOAD position, spool (4) is moved down. Oil from passage (10) now goes around the spool into port (3). Most of this oil goes to the head end of the cylinder. The bucket loads (closes or curls). Some of the oil in port (3) goes through passage (6). Then it goes to the resolver network to adjust the pump as required by the load. The oil from the rod end is forced out of the cylinder through port (2), around spool (4), through signal passage (14) and tank passage (15) to tank. In the LOAD position, pressure in cavity (12) is equal to the pressure in passage (6). Spring (16) is compressed from the top in this spool position. When the control lever is released, spring (16) returns to normal position. This pushes the control lever back into HOLD position. See LINE RELIEF AND MAKEUP VALVE for the operation of item (1).

Dump Position

Bucket Valve (DUMP Position)
(2) Port to rod end of cylinder. (3) Port to head end. (4) Control spool. (5) Passage to tank. (6) Signal passage. (10) Passage. (12) Signal cavity. (14) Signal passage. (15) Passage to tank. (16) Spring.

In the DUMP Position, spool (4) is moved up. Oil from passage (10) now goes around the spool into port (2). Most of the oil goes to the rod end of the cylinder. The bucket dumps (opens). Some of the oil in port (2) goes through passage (14). Then this oil goes to the resolver network to adjust the pump as required by the load. The oil from the head end is forced out of the cylinder through port (3), around spool (4), through signal passage (6) and tank passage (5) to tank. In the DUMP position, pressure in passage (12) is equal to the pressure in passage (14).

Spring (16) is compressed from the bottom in this spool position. When the control lever is released, spring (16) returns to normal position. This pushes the control lever back into HOLD position.

Bucket Valve 9T7171

Hold Position

Bucket Valve (HOLD Position)
(1) Makeup and relief valve. (2) Port to rod end of cylinder. (3) Port to head end of cylinder. (4) Main control spool. (5) Passages to tank. (6) Signal passages to primary resolver. (7) Spring. (8) Load check valve. (9) Spool. (10) Pump passage. (11) Passage. (12) Passage. (13) Spring. (14) Passage. (15) Signal passage to primary resolver. (16) Passage to tank. (17) Spring.

The location of the control valve section for the backhoe bucket is between the control valve section for swing and the control valve section for stick. Spring (17) on the end of valve spool (4) is compressed when the spool is moved to either the DUMP or LOAD position. The spring will move valve spool (4) and the control lever to HOLD when the lever is released.

Pump oil from the valve section for the stick enters the bucket valve section through passage (10). This passage is common through all of the valve sections. Passage (10) has no outlet. At first, pump oil can only get into small passage (11) between load check valve (8) and compensator spool (9). Pump pressure continues to build. When the pressure is high enough, load check valve (8) is moved up against the force of spring (7). This higher than normal pressure now fills the area between load check valve (8) and compensator spool (9). This causes compensator spool (9) to move down against the combined signal pressure from passage (15) and the force of spring (13) in passage (14). When compensator spool (9) moves down far enough, the small holes in the spool begin to close off pump passage (10). A restriction is created. Pressure inside spool (9) is 415 kPa (60 psi) greater than the pressure in passage (14). The pressure inside spool (9) is the same as the pressure in pump passage (10). This oil now can flow through compensator spool (9) into passage (12).

In HOLD position, spool (4) stops pressure oil in passage (12) from going into port (2) and (3). The oil in port (3) to the head end of the bucket cylinder is blocked. The oil in port (2) to the rod end of the bucket cylinder is also blocked. The bucket is now held in location. The oil in passage (5), (6), (14), (15) and (16) goes to drain.

Spring (17) now holds spool (4) in this position.

Load Position

Bucket Valve (LOAD Position)
(1) Makeup and relief valve. (2) Port to rod end of cylinder. (3) Port to head end of cylinder. (4) Main control spool. (5) Passages to tank. (6) Signal passages to primary resolver. (7) Spring. (8) Load check valve. (9) Spool. (10) Pump passage. (12) Passage. (13) Spring. (14) Passage. (15) Signal passage to primary resolver. (16) Passage to tank. (17) Spring.

In the LOAD position, spool (4) is moved down. Oil from passage (12) now goes around the spool into port (3). Most of this oil goes to the head end of the cylinder. The bucket loads (closes or curls). Some of the oil in port (3) goes through passage (6). Then it goes to the resolver network to adjust the pump as required by the load. The oil from the rod end is forced out of the cylinder through port (2), around spool (4), through signal passage (15) and tank passage (16) to tank. In the LOAD position, pressure in passage (14) is equal to the pressure in passage (6). Spring (17) is compressed from the top in this spool position. When the control lever is released, spring (17) returns to normal position. This pushes the control lever back into HOLD position. See LINE RELIEF AND MAKEUP VALVE for the operation of item (1).

Dump Position

Bucket Valve (DUMP Position)
(1) Makeup and relief valve. (2) Port to rod end of cylinder. (3) Port to head end of cylinder. (4) Main control spool. (5) Passages to tank. (6) Signal passages to primary resolver. (7) Spring. (8) Load check valve. (9) Spool. (10) Pump passage. (12) Passage. (13) Spring. (14) Passage. (15) Signal passage to primary resolver. (16) Passage to tank. (17) Spring.

In the DUMP Position, spool (4) is moved up. Oil from passage (12) now goes around the spool into port (2). Most of the oil goes to the rod end of the cylinder. The bucket dumps (opens). Some of the oil in port (2) goes through passage (15). Then this oil goes to the resolver network to adjust the pump as required by the load. The oil from the head end is forced out of the cylinder through port (3), around spool (4), through signal passage (6) and tank passage (5) to tank. In the DUMP position, pressure in passage (14) is equal to the pressure in passage (15).

Spring (17) is compressed from the bottom in this spool position. When the control lever is released, spring (17) returns to normal position. This pushes the control lever back into HOLD position.

Swing Valve

Swing Valve (HOLD Position)
(1) Makeup and relief valve. (2) Port to cylinders. (3) Port to cylinders. (4) Control spool. (5) Passages to tank. (6) Signal passage. (7) Spool. (8) Holes. (9) Pump passage. (10) Passage. (11) Spring. (12) Signal cavity. (13) Signal port. (14) Signal passage. (15) Passage to tank. (16) Spring.

The location of the control valve section for the backhoe swing is between the control valve section for boom and the control valve section for bucket.

Spring (16) on the end of valve spool (4) is compressed when the spool is moved to either the RIGHT or LEFT position. The spring will move valve spool (4) and the control lever to HOLD when the lever is released.

Pump oil from the valve section for the bucket enters the swing valve section through passage (9). Passage (9) is a common passage through all of the valve sections. Passage (9) has no outlet. The pump oil goes through holes (8) into spool (7). This causes the spool to move down against the combined signal pressure from port (13) and the force of spring (11) in cavity (12). When holes (8) begin to close off pump passages (9), there is a restriction created which limits pressure inside spool (7) to 415 kPa (60 psi) greater than the pressure in signal cavity (12). The pressure inside spool (7) is the same as the pressure in passage (10).

Hold Position

In HOLD position, spool (4) stops pressure oil in passage (10) from going into ports (2) and (3). The oil in port (3) to the rod end of the left cylinder is blocked. The oil in port (2) to the rod end of the right cylinder is also blocked. The backhoe is now held in location. The oil in passages (5), (6), (12), (14) and (15) goes to drain.

Spring (16) now holds spool (4) in this position.

Swing Right

NOTE: The terms right and left are determined by the position of the operator when seated in the backhoe operating position.

To swing right (not shown), spool (4) is moved down. As the spool starts to move, hole (B) gets pump oil and sends it through hole (A) to signal passage (6). This advance signal causes the pump to upstroke. Next, work port (2) opens to signal passage (6). Pump output adjusts to work port requirements plus margin pressure. Now pump oil in passage (10) opens to work port (3). This oil enters the rod end of right swing cylinder (22). Part of this oil goes through line (21) to the head end of left swing cylinder (18). Right cylinder (22) retracts. Left cylinder (18) extends. Oil from the head end of cylinder (22) is forced through line (19). This oil joins with the rod end oil from cylinder (18) and goes through port (2), passage (14) and passage (15) to drain. The boom now swings right.

Swing Left

Swing Control (Swinging Left)
(2) Outlet to cylinders (for left swing) OR Return from cylinders (for right swing). (3) Outlet to cylinders (for right swing) OR Return from cylinders (for left swing). (4) Control spool. (5) Passage to tank. (6) Signal passage. (10) Pump passage. (14) Signal passage. (15) Passage to tank. (16) Spring. (17) Left cylinder relief valve. (18) Left cylinder. (19) Cylinder-to-cylinder crossover. (20) Orifice check valve. (21) Cylinder-to-cylinder crossover. (22) Right cylinder. (23) Right cylinder relief valve. (24) Cylinder, head end snubber. (A) Signal hole. (B) Pump signal hole. (C) Pump signal hole. (D) Signal hole.

To swing left, spool (4) is moved up. As the spool starts to move, hole (C) gets pump oil and sends it through hole (D) to signal passage (14). This advance signal causes the pump to upstroke. Next, work port (2) opens to signal passage (14). Pump output adjusts to work port requirements plus margin pressure. Now pump oil in passage (10) opens to work port (2). This oil enters the rod end of left swing cylinder (18). Part of this oil goes through line (19) to the head end of right swing cylinder (22). Left cylinder (18) retracts. Right cylinder (22) extends. Oil from the head end of cylinder (18) is forced through line (21). This oil joins with the rod end oil from cylinder (22) and goes through port (3), passage (6) and passage (5) to drain. The boom now swings left.

When the operator releases the swing control lever from either the RIGHT or LEFT position, spring (16) will force spool (4) and the control lever back to HOLD.

There are two cylinder-to-cylinder crossover lines. Line (19) connects the rod end of swing cylinder (18) to the head end of swing cylinder (22). Line (21) connects the rod end of cylinder (22) to the head end of cylinder (18). Each line has an orifice check valve (20). Remember that to swing, the rod end of one cylinder is pressurized while the head end of the other cylinder is pressurized. The head end has a larger area for the pressure to act on. Therefore, pressure to the head end must be reduced so there will be equal forces acting on both the rod and head ends. These valves, along with the metering characteristics of spool (4), provide uniform swing speed.

There is one rod to head chamber crossover line per swing cylinder. The crossover line for cylinder (18) has relief valve (17). The crossover line for cylinder (22) has relief valve (23). These valves are the same.

Crossover Relief Valve

Crossover Relief Valve
(1) Adjusting screw. (2) Locknut. (3) Valve body. (4) Spring. (5) Valve. (6) Outlet. (7) Inlet.

Under normal conditions, spring (4) pushes valve (5) down. In this seated position, oil in inlet passage (7) is blocked. When the backhoe boom swing is stopped abruptly, the oil pressure in passage (7) increases. If this increase is great enough, valve (5) moves up against the force of spring (4). The oil in passage (7) from the cylinder head end now goes out passage (6). This oil goes to the rod end of the cylinder. Basically, the relief valve limits the pressure difference across the cylinder to about 19 300 kPa (2800 psi). This helps stop cavitation.

Swing Valve 9T7933

Hold Position

Swing Valve (HOLD Position)
(1) Makeup and relief valve. (2) Control spool. (3) Passage to tank. (4) Signal passage. (5) Stem passage. (6) Spool. (7) Holes. (8) Pump passage. (9) Stem passage. (10) Passage. (11) Spring. (12) Passage. (13) Signal Passage. (14) Passage to tank. (15) Spring. (16) Signal metering slots. (17) Check ball. (18) Port to cylinders. (19) Stem signal passage. (20) Stem passage. (21) Port to cylinders. (22) Stem signal passage. (23) Stem passage. (24) Check ball. (25) Metering slots.

The location of the control valve section for the backhoe swing is between the control valve section for boom and the control valve section for bucket.

Spring (15) on the end of valve spool (2) is compressed when the spool is moved to either the RIGHT or LEFT position. The spring will move valve spool (2) and the control lever to HOLD when the lever is released.

Pump oil from the valve section for the bucket enters the swing valve section through passage (8). Passage (8) is a common passage through all of the valve sections. Passage (8) has no outlet. The pump oil goes through holes (7) into spool (6). This causes the spool to move down against the combined signal pressure from passage (13) and the force of spring (11) in passage (12). When holes (7) begin to close off pump passages (8), there is a restriction created which limits pressure inside spool (6) to 415 kPa (60 psi) greater than the pressure in signal passage (12). The pressure inside spool (6) is the same as the pressure in passage (10).

In HOLD position, stem passages (20) and (23) are open a small amount to passage (10). Oil goes from passage (10) through stem passages (20) and (23), past check balls (17) and (24), and through stem passages (4) and (9) into cylinder ports (18) and (21). Compensator spool (6) and springs (11) keep the oil in cylinder ports (18) and (21) at 550 to 620 kPa (80 to 90 psi). This keeps the cylinder lines full of oil at all times to make the swing movement more precise. The oil in port (21) to the rod end of the left cylinder is blocked by check ball (24). The oil in port (18) to the rod end of the right cylinder is blocked by check ball (17). The backhoe is now held in location. The oil in passages (5), (6), (12), (14) and (15) goes to drain.

Spring (15) now holds spool (2) in this position.

Swing Right

Swing Valve (Swing RIGHT Position)
(1) Makeup and relief valve. (2) Control spool. (3) Passage to tank. (4) Signal passage. (5) Stem passage. (6) Spool. (7) Holes. (8) Pump passage. (9) Stem passage. (10) Passage. (11) Spring. (12) Passage. (13) Signal Passage. (14) Passage to tank. (15) Spring. (16) Signal metering slots. (17) Check ball. (18) Port to cylinders. (19) Stem signal passage. (20) Stem passage. (21) Port to cylinders. (22) Stem signal passage. (23) Stem passage. (24) Check ball. (25) Metering slots.

NOTE: The terms right and left are determined by the position of the operator when seated in the backhoe operating position.

To swing right, spool (2) is moved down. As the spool begins to move, stem passage (22) is uncovered and sends pump oil to signal passage (4). Signal metering slots (25) close signal passage (4) to passage to tank (3). This advance signal causes the pump to upstroke. The signal metering slots cause a gradual increase in signal and pump oil pressure. This helps the boom to swing more smoothly. Pump output now adjusts to work port requirements plus margin pressure. Oil from pump passage (10) now goes through stem passage (23), moves check ball (24) off it's seat and goes through stem passage (5) into cylinder port (21). This oil enters the rod end of right swing cylinder (31). Part of this oil goes through line (30) to the head end of left swing cylinder (27). Right cylinder (31) retracts. Left cylinder (27) extends. Oil from the head end of cylinder (31) is forced through line (28). This oil joins with the rod end oil from cylinder (27) and goes through port (18), stem passage (20), past check ball (17), through stem passage (9) and passage (13) to drain (14). The boom now swings right.

Swing Left

Swing Valve (Swinging Left)
(1) Makeup and relief valve. (2) Control spool. (3) Passage to tank. (4) Signal passage. (5) Stem passage. (6) Spool. (7) Holes. (8) Pump passage. (9) Stem passage. (10) Passage. (11) Spring. (12) Passage. (13) Signal Passage. (14) Passage to tank. (15) Spring. (16) Signal metering slots. (17) Check ball. (18) Port to cylinders. (19) Stem signal passage. (20) Stem passage. (21) Port to cylinders. (22) Stem signal passage. (23) Stem passage. (24) Check ball. (25) Metering slots. (26) Left cylinder relief valve. (27) Left cylinder. (28) Cylinder-to cylinder crossover. (29) Orifice. (30) Cylinder-to-cylinder crossover. (31) Right cylinder. (32) Right cylinder relief valve. (33) Cylinder, head end snubber.

NOTE: The terms right and left are determined by the position of the operator when seated in the backhoe operating position.

To swing left, spool (2) is moved up. As the spool begins to move, stem passage (19) is uncovered and sends pump oil to signal passage (13). Signal metering slots (16) close signal passage (13) to passage to tank (14). This advance signal causes the pump to upstroke. The signal metering slots cause a gradual increase in signal and pump oil pressure. This helps the boom to swing more smoothly. Pump output now adjusts to work port requirements plus margin pressure. Oil from pump passage (10) now goes through stem passage (20), moves check ball (17) off it's seat and goes through stem passage (9) into cylinder port (18). This oil enters the rod end of left swing cylinder (27). Part of this oil goes through line (28) to the head end of right swing cylinder (31). Left cylinder (27) retracts. Right cylinder (31) extends. Oil from the head end of cylinder (27) is forced through line (30). This oil joins with the rod end oil from cylinder (31) and goes through port (21), stem passage (22), past check ball (23), through stem passage (5) and passage (4) to drain (3). The boom now swings left.

There are two cylinder-to-cylinder crossover lines. Line (28) connects the rod end of swing cylinder (27) to the head end of swing cylinder (31). Line (30) connects the rod end of cylinder (31) to the head end of cylinder (27). Each line has an orifice (29). Remember that to swing, the rod end of one cylinder is pressurized while the head end of the other cylinder is pressurized. The head end has a larger area for the pressure to act on. Therefore, pressure to the head end must be reduced so there will be equal forces acting on both the rod and head ends. These orifices, along with the metering characteristics of spool (2), provide uniform swing speed.

There is one rod to head chamber crossover line per swing cylinder. The crossover line for cylinder (27) has relief valve (26). The crossover line for cylinder (31) has relief valve (32). These valves are the same.

Crossover Relief Valve

Crossover Relief Valve
(1) Adjusting screw. (2) Locknut. (3) Valve body. (4) Spring. (5) Valve. (6) Outlet. (7) Inlet.

Under normal conditions, spring (4) pushes valve (5) down. In this seated position, oil in inlet passage (7) is blocked. When the backhoe boom swing is stopped abruptly, the oil pressure in passage (7) increases. If this increase is great enough, valve (5) moves up against the force of spring (4). The oil in passage (7) from the cylinder head end now goes out passage (6). This oil goes to the rod end of the cylinder. Basically, the relief valve limits the pressure difference across the cylinder to about 19 300 kPa (2800 psi). This helps stop cavitation.

Boom Valve

Boom Valve (HOLD Position)
(1) Line makeup and relief valve. (2) Port to rod end. (3) Port to head end. (4) Control spool. (5) Passage to tank. (6) Signal passage. (7) Spring. (8) Load check valve. (9) Compensator spool. (10) Pump passage. (11) Passage. (12) Passage. (13) Spring. (14) Signal cavity. (15) Signal port. (16) Signal passage. (17) Passage to tank. (18) Spring.

The location of the control valve for the boom is between the control valve sections for swing and for the left stabilizer.

Spring (18) on the end of valve spool (4) is compressed when the spool is moved to either the RAISE or DOWN position. The spring will move valve spool (4) and the control lever to HOLD when the lever is released.

Pump oil from the valve section for the swing enters the boom valve section through passage (10). This passage is common through all of the valve sections. Passage (10) has no outlet. At first, pump oil can only get into small passage (11) between load check valve (8) and compensator spool (9). Pump pressure continues to build. When the pressure is high enough, load check valve (8) is moved up against the force of spring (7). This higher than normal pressure now fills the area between load check valve (8) and compensator spool (9). This causes compensator spool (9) to move down against the combined signal pressure from port (15) and the force of spring (13) in cavity (14). When compensator spool (9) moves down far enough, the small holes in the spool begin to close off pump passage (10). A restriction is created. Pressure inside spool (9) to 415 kPa (60 psi) greater than the pressure in signal cavity (14). The pressure inside spool (9) is the same as the pressure in passage (10). This oil now can flow through compensator spool (9) into passage (12).

Hold Position

In HOLD position, control spool (4) stops pressure oil in passage (12) from going to ports (2) and (3). The oil in port (2) to the head end of the boom cylinder is blocked. The oil in port (3) to the rod end is also blocked. The boom is now held in location. The oil in passages (5), (6), (16) and (17) goes to drain.

Spring (18) now holds control spool (4) in this position.

Down Position

Boom Valve Section (DOWN Position)
(2) Port to rod end. (3) Port to head end. (4) Control spool. (5) Passage to tank. (6) Signal passage. (12) Passage. (14) Signal cavity. (16) Signal passage. (17) Passage to tank. (18) Spring.

In the DOWN position, spool (4) is moved down. Oil from passage (12) now goes around spool (4) to port (3). Most of this oil goes to the head end of the boom cylinders. The boom cylinders extend and the boom goes down. Some of the oil from port (3) goes to signal passage (6). The oil goes to the resolver network to adjust the pump as required by the load. The oil from the rod end of the boom cylinders is forced out. This oil enters port (2). The oil goes past spool (4) to signal passage (16). Finally, this oil goes through passage (17) to tank. In the DOWN position, pressure in cavity (14) is the same as the pressure in passage (6). Spring (18) is compressed from the top. When the control lever is released, spring (18) moves spool (4) into the HOLD position.

Raise Position

Boom Valve Section (RAISE Position)
(2) Port to rod end. (3) Port to head end. (4) Control spool. (5) Passage to tank. (6) Signal passage. (12) Passage. (14) Signal cavity. (16) Signal passage. (17) Passage to tank. (18) Spring.

In the RAISE position, spool (4) is moved up. As the spool starts to move, hole (A) gets pump oil. This oil goes through hole (B) to signal passage (16). This advanced signal causes the pump to upstroke. As the spool moves farther up, high pressure oil goes past spool (4) to port (2). This oil has a high enough pressure to prevent boom droop. The oil goes to the rod end of the boom cylinders. The cylinders retract. The boom moves up. Some of the oil from port (2) goes to passage (16). The oil now goes to the resolver network to adjust the pump output as required by the actual load. Oil from the head end of the cylinders is forced out. This oil enters port (3). The oil goes past spool (4) to signal passage (6). Finally, this oil goes through passage (5) to tank. In the RAISE position, pressure in cavity (14) is the same as the pressure in passage (16). Spring (18) is compressed from the bottom. When the control lever is released, spring (18) moves spool (4) into the HOLD position.

Boom Valve 9T7934

Boom Valve (HOLD Position)
(1) Line makeup and relief valve. (2) Port to rod end. (3) Port to head end. (4) Control spool. (5) Passage to tank. (6) Signal passage. (7) Spring. (8) Load check valve. (9) Compensator spool. (10) Pump passage. (11) Passage. (12) Passage. (13) Springs. (14) Signal passage. (15) Signal passage. (16) Passage to tank. (17) Spring. (A) Signal hole. (B) Pump signal hole. (C) Pump signal hole. (D) Signal hole.

The location of the control valve for the boom is between the control valve sections for the swing and for the left stabilizer.

Spring (17) on the end of valve spool (4) is compressed when the spool is moved to either the IN or OUT position. The spring will move valve spool (4) and the control lever to HOLD when the lever is released.

Pump oil from the valve section for the left stabilizer enters the boom valve section through passage (10). This passage is common through all of the valve sections. Passage (10) has no outlet. At first, pump oil can only get into small passage (11) between load check valve (8) and compensator spool (9). Pump pressure continues to build. When the pressure is high enough, load check valve (8) is moved up against the force of spring (7). This higher than normal pressure now fills the area between load check valve (8) and compensator spool (9). This causes compensator spool (9) to move down against the combined signal pressure from port (15) and the force of spring (13) in passage (14). When compensator spool (9) moves down far enough, the small holes in the spool begin to close off pump passage (10). A restriction is created. Pressure inside spool (9) is 415 kPa (60 psi) greater than the pressure in signal passage (14). The pressure inside spool (9) is the same as the pressure in passage (10). This oil now can flow through compensator spool (9) into passage (12).

Hold Position

In HOLD position, control spool (4) stops pressure oil in passage (12) from going to ports (2) and (3). The oil in port (2) to the head end of the stick cylinder is blocked. The oil in port (3) to the rod end is also blocked. The stick is now held in location. The oil in passages (5), (6), (15) and (16) goes to drain.

Spring (17) now holds control spool (4) in this position.

Down Position

Boom Valve Section (DOWN Position)
(1) Line makeup and relief valve. (2) Port to rod end. (3) Port to head end. (4) Control spool. (5) Passage to tank. (6) Signal passage. (7) Spring. (8) Load check valve. (9) Compensator spool. (10) Pump passage. (11) Passage. (12) Passage. (13) Springs. (14) Signal passage. (15) Signal passage. (16) Passage to tank. (17) Spring. (A) Signal hole. (B) Pump signal hole. (C) Pump signal hole. (D) Signal hole.

In the DOWN position, spool (4) is moved down. As the spool starts to move, hole (B) gets pump oil and sends it through hole (B). This oil goes to signal passage (6) and causes the pump to upstroke. Then, when the spool moves down far enough, pump oil from passage (10) goes past spool (4) into port (3). The pump oil pressure is now high enough to prevent boom droop.

Oil from passage (12) now goes around spool (4) to port (3). Most of this oil goes to the head end of the boom cylinders. The boom cylinders extend and the boom goes down. Some of the oil from port (3) goes to signal passage (6). The oil goes to the resolver network to adjust the pump as required by the load. The oil from the rod end of the boom cylinders is forced out. This oil enters port (2). The oil goes past spool (4) to signal passage (15). Finally, this oil goes through passage (16) to tank. In the DOWN position, pressure in passage (14) is the same as the pressure in passage (6). Spring (17) is compressed from the top. When the control lever is released, spring (17) moves spool (4) into the HOLD position.

Raise Position

Boom Valve Section (RAISE Position)
(1) Line makeup and relief valve. (2) Port to rod end. (3) Port to head end. (4) Control spool. (5) Passage to tank. (6) Signal passage. (7) Spring. (8) Load check valve. (9) Compensator spool. (10) Pump passage. (11) Passage. (12) Passage. (13) Springs. (14) Signal passage. (15) Signal passage. (16) Passage to tank. (17) Spring. (A) Signal hole. (B) Pump signal hole. (C) Pump signal hole. (D) Signal hole.

In the RAISE position, spool (4) is moved up. As the spool starts to move, hole (C) gets pump oil. This oil goes through hole (D) to signal passage (15). This advanced signal causes the pump to upstroke. As the spool moves farther up, high pressure oil goes past spool (4) to port (2). This oil has a high enough pressure to prevent boom droop. The oil goes to the rod end of the boom cylinders. The cylinders retract. The boom moves up. Some of the oil from port (2) goes to passage (15). The oil now goes to the resolver network to adjust the pump output as required by the actual load. Oil from the head end of the cylinders is forced out. This oil enters port (3). The oil goes past spool (4) to signal passage (6). Finally, this oil goes through passage (5) to tank. In the RAISE position, pressure in passage (14) is the same as the pressure in passage (15). Spring (17) is compressed from the bottom. When the control lever is released, spring (17) moves spool (4) into the HOLD position.

Signal Resolver Network

Resolver Network Line Schematic
(1) Primary resolver. (2) Secondary resolver.

Each control valve section in the implement hydraulic system has two resolvers, a primary resolver and a secondary resolver. Each resolver compares two pressure signals. The higher of the two signals goes to the next resolver.

Typical Control Valve
(1) Primary resolver. (2) Secondary resolver.

The primary resolver is installed parallel to the control spool. The ball check is built into the resolver. The secondary resolver is installed perpendicular to the primary resolver. The ball check is not contained in a housing. A plug holds the ball check in the valve body.

Check Valve
(3) Signal line from cylinder head end. (4) Outlet line. (5) Ball check. (6) Signal line from the rod end.

Partial Resolver Network Section Schematic
(1) Primary resolver. (2) Secondary resolver.

The primary resolver compares the pressure between the two work ports in each control valve section. In other words, it compares the head end pressure of the cylinder to the rod end pressure of the same cylinder.

In the previous illustration, the head end pressure in line (3) is greater than the rod end pressure in line (6). The head end pressure forces ball check (5) left. This blocks line (6). The pressure in line (3) is now the highest resolved pressure in this resolver. This pressure can now go through outlet line (4) to the next resolver.

The secondary resolver in each valve section works similarly. It compares the pressure signals between two valve sections. In other words, the secondary resolver compares the highest primary pressure signal in its control valve to the highest resolved signal from the previous control valve.

The signal network is arranged in series. It starts at the backhoe section. The secondary resolver in the last backhoe control valve section is connected to the first secondary resolver of the loader control valve section. The highest resolved signal pressure from the backhoe section goes to the loader section. The highest resolved signal from the loader section goes to the steering sections secondary resolver. The highest resolved signal from the steering section (HMU) goes to the compensator valve on the pump. This signal now instructs the pump to vary its output to meet the highest resolved load requirements. The compensator valve adds margin pressure to the load requirements. Note that the resolver network does not add the various loads together. Instead, the single highest resolved load plus margin governs pump output. Therefore, the entire system is supplied with 1380-1700 kPa (200-245 psi) more pressure than necessary to handle the single largest load. The pump will not change its output until the resolver network identifies a different highest resolved signal.

Hydraulic Cylinders

Cylinder Identification Right Side Of Machine

The backhoe and loader cylinders are the threaded gland design. The rod end assembly is called the gland. It houses the wear band, buffer seal, U-cup seal and wiper. The gland is threaded into the expanded rod end of the cylinder. This keeps the gland threads bathed in oil to prevent them from corroding.

Basic Hydraulic Cylinder

The piston is secured to the rod with a bolt and washer. The piston incorporates wear band and oil seal.

Loader Lift Cylinders

There are two loader lift cylinders (basic design). One is mounted on each side of the loader tower. When the head ends are pressurized, the cylinder will extend and the loader will raise. Pressurizing the rod end will lower the loader.

A lock bar and pin are located on the right lift cylinder. The lock bar should be installed on the cylinder if the loader has to be raised during repairs or servicing. During normal operation, store the lock bar on the loader arm.

Loader Tilt Cylinder

The loader bucket cylinder (basic design) is mounted on the tilt linkage. The linkage connects the cylinder to the bucket and lift arm cross tube. The rod is connected to the bucket. When the head end of the cylinder is pressurized, the bucket will tilt back. The bucket will dump when the rod end is pressurized.

Multi-Purpose Bucket Cylinders

The multi-purpose bucket (not shown) has clam cylinders (basic design) on each end of the bucket. When the rod ends of the cylinder are pressurized, the clam will open. Pressurizing the head ends will close the clam.

Backhoe Boom Cylinders

The backhoe boom has two cylinders (basic design). One is mounted on each side of the boom. When the head ends of the cylinders are pressurized, the boom lowers. Pressurizing the rod ends raises the boom.

The boom is an over-center design. The operator can shift the backhoe over center toward the cab when he is ready to transport the vehicle. A transport lock secures the backhoe in the transport position. This feature shifts the center of gravity of the backhoe as far forward as possible to provide for better roadability. It also increases the bucket ground clearance.

Backhoe Stick Cylinder

The stick cylinder (basic design) is mounted on the boom. When the head end is pressurized, the stick dips down. Pressurizing the rod end raises or extends the stick, thus increasing the backhoe reach.

Backhoe Bucket Cylinder

The bucket cylinder is mounted on the stick. The cylinder rod is connected to a four bar linkage which is connected to the bucket. When the cylinder head end is pressurized, the bucket will load (close or curl). Pressurizing the rod end will rotate the bucket to open.

Bucket Cylinder
(1) Cylinder body. (2) Cylinder piston. (3) Spring. (4) Snubber piston. (5) Snubber orifice. (6) Head. (7) Ring.

NOTE: Later machines do not use the rod end snubber.

The bucket cylinder has an integral rod end snubber. The snubber consists of spring (3) and snubber piston (4) with its orifice (5). The snubber cushions the bucket as it hits the load (curl) stop. Pressurizing the head end extends the cylinder. This loads the bucket. When cylinder piston (2) moves right far enough, snubber piston (4) contacts head (6). The oil between cylinder piston (2) and snubber piston (4) is forced through snubber orifice (5). The orifice restricts oil flow out of body (1). The flow restriction cushions the impact. Spring (3) does not provide the cushion. Spring (3) holds snubber piston (4) against ring (7).

Backhoe Swing Cylinders

The backhoe swing cylinders are located in the rear of the main frame. The cylinders are trunnion mounted to the main frame and are retained by a single piece trunnion cap. The cylinder rods are connected to the swing frame.

Swing Cylinder
(1) Cylinder body. (2) Rod end. (3) Spring. (4) Snubber. (5) Head end. (6) Head end port.

The swing cylinders have integral head end snubbers (4). The snubbers cushion the swing frame before it contacts the machine frame. As the cylinder retracts, snubber (4) enters head end port (6). The oil trying to leave the head end chamber is restricted. This reduces piston speed thus creating a cushioning effect.

When head end (5) is pressurized, snubber (4) is moved left against the force of spring (3). The restriction is eliminated. The cylinder piston returns to normal operation. Now pressure entering head end port (6) forces the cylinder piston to the left. Also see SWING VALVE.

Stabilizer Cylinders

The stabilizer cylinders (basic design) are mounted on the rear corners of the main frame. The rod ends are connected to the stabilizers. Pressurizing the head ends through the lock valve, as explained earlier, lowers the stabilizers and raises the tractor. Pressurizing the rod ends raises the stabilizers, thus returning the tractor's tires to the ground. When the stabilizers are fully raised, they are within the overall tire width. Also see STABILIZER VALVES.