Usage:
General Information
SMCS Code: 5050
Schematic of the Hydraulic System
(1) Tilt cylinder. (2) Lift cylinders. (3) Ride control accumulator. (4) Main control valve. (5) Autodig pressure sensor connection ports. (6) Ride control diverter valve. (7) Tilt cylinder rod end line relief valve. (8) Tilt cylinder head end line relief valve. (9) Ride control relief valve. (10) Tilt control valve spool. (11) Lift control valve spool. (12) Main relief valve. (13) Lift circuit relief valve. (14) Lift arm positioner valve. (15) Float sequence valve. (16) Breaker relief valve. (17) Hydraulic filter group. (18) Hydraulic tank. (19) Pilot control valve. (20) Check valves. (21) Manifolds. (22) Pilot oil pressure reducing valve. (23) Selector and pressure control valve. (24) Main implement pump. (25) Torque converter scavenge pump. (26) Brake and pilot pump. (27) Steering pump. (AA) Pressure test point for rod end of tilt cylinder. (BB) Pressure test point for head end of tilt cylinder. (CC) Pressure test point for main hydraulic system.
Location of the Hydraulic System Components
(1) Tilt cylinder. (2) Lift cylinders. (3) Ride control accumulator. (4) Main control valve. (6) Ride control diverter valve. (13) Lift circuit relief valve. (14) Lift arm positioner valve. (15) Float sequence valve. (18) Hydraulic tank. (19) Pilot control valve. (22) Pilot oil pressure reducing valve. (23) Selector and pressure control valve. (24) Main implement pump. (26) Brake and pilot pump.
The implement hydraulic system has two circuits; the pilot oil circuit and the main circuit. The main (implement) oil system is an open center system controlled by the pilot oil system.
The main components of the pilot circuit are hydraulic tank (18), brake and pilot pump (26), pilot oil pressure reducing valve (22), selector and pressure control valve (23), pilot control valve (19), lift arm positioner valve (14) and float sequence valve (15).
The components of the main implement circuit are hydraulic tank (18), hydraulic filter group (17), main implement pump (24), main relief valve (12), main control valve (4), tilt cylinder (1) and lift cylinders (2).
Location of the Hydraulic Tank and Filter Group
(17) Filter group (under cover). (18) Hydraulic tank (behind guard). (28) Hydraulic tank filler cap.
Hydraulic tank (18) is located in the middle of the right side of the machine behind the hydraulic tank guard. Additional oil is placed into the tank by removing filler cap (28). The hydraulic system has filter group (17) in hydraulic tank (18). If the oil restriction through the filters is too high (filter elements too dirty), a filter bypass valve in the tank will open and allow oil to bypass the filters and return to the tank.
Location of the Breaker Relief Valve
(16) Breaker relief valve. (18) Hydraulic tank.
Breaker relief valve (16) is mounted on hydraulic tank (18).
Location of the Main Implement Pump
(24) Main implement pump. (25) Torque converter scavenge pump.
Main implement pump (24) is mounted on the torque converter updrive housing. Main implement pump (24) provides the oil to operate the lift and tilt cylinders. The oil goes to main control valve (4). This valve is an open center valve with two spools; one for the bucket lift and lower and one for the bucket tilt back and dump. The oil from the pilot system causes movement of the valve spools. When the valve spools are in the HOLD position, the oil goes through main control valve (4) and back to the tank.
Location of the Steering, Brake and Pilot Pump
(26) Brake and pilot pump section. (27) Steering pump section.
Brake and pilot pump (26) is part of a two section, gear pump mounted on the torque converter updrive housing. The brake and pilot section of the pump is used for the parking brake, the service brake, and the pilot oil for the steering and implement systems.
Reference: For more information on the steering system, refer to Steering System, Systems Operation, Testing and Adjusting for the machine that is being serviced.
Reference: For more information on the braking system, refer to Braking System, Systems Operation, Testing and Adjusting for the machine that is being serviced.
Location of the Main Control Valve
(4) Main control valve.
Main control valve (4) is located in the center of the front frame. The main control valve directs the oil from main implement pump (24) to the lift and tilt cylinders.
Location of the Main Relief Valve
(12) Main relief valve.
Location of the Tilt Cylinder Line Relief Valves
(7) Tilt cylinder rod end line relief valve. (8) Tilt cylinder head end line relief valve.
Included in the main control valve housing are main relief valve (12), tilt cylinder rod end line relief valve (7) and tilt cylinder head end line relief valve (8).
When the pressure from the implement hydraulic pump exceeds the setting of main relief valve (12), the relief valve opens to send the flow of oil to hydraulic tank (18).
Line relief valves (7) and (8) protect the tilt cylinder from external shocks. When the pressure in the tilt cylinder exceeds the setting of either relief valve, the relief valve opens to vent the excess pressure to tank.
Location of the Lift Circuit Relief Valve
(13) Lift circuit relief valve.
Lift circuit relief valve (13) protects the main control valve, ride control accumulator and ride control components from high pressure spikes.
Location of the Pilot Oil Pressure Reducing Valve
(22) Pilot oil pressure reducing valve.
Pilot oil pressure reducing valve (22) is mounted on the left side of the rear frame in the transmission compartment.
Oil for the pilot circuits is drawn from the tank by brake and pilot pump (26). The pilot oil then flows through a check valve to pilot oil pressure reducing valve (22). The pilot oil, now at a reduced pressure, flows through a check valve to selector and pressure control valve (23) and on to pilot control valve (19) for use in the implement hydraulic system.
Location of the Pilot Control Valve
(19) Pilot control valve (behind cover). (29) Hydraulic control lever.
Pilot control valve (19) is located on the right side of the operator's station. Hydraulic control lever (29) controls all bucket movement.
The pilot oil is blocked at the pilot control valve when the hydraulic control lever is in the HOLD position. Moving the hydraulic control lever will send pilot oil to main control valve (4) to move tilt spool (10) or lift spool (11).
Location of the Selector and Pressure Control Valve
(23) Selector and pressure control valve.
Selector and pressure control valve (23) is mounted on the left side of the rear frame in the transmission compartment.
Selector and pressure control valve (23) provides pilot oil to pilot control valve (19) to lower the bucket when the engine is off. High pressure oil from the lift cylinders enters the pilot system through selector and pressure control valve (23). The selector and pressure control valve reduces the oil pressure and lets lower pressure oil flow to the pilot control valve. When the hydraulic control lever is moved to the LOWER position, pilot oil flows to the lift spool in the main control valve which allows the bucket to be lowered.
Location of the Lift Arm Positioner Valve
(14) Lift arm positioner valve.
Lift arm positioner valve (14) is mounted on the left side of the rear frame near the articulation hitch area of the machine.
Lift arm positioner valve (14) controls the movement of the lift arms during lowering. When the lift arm positioner valve is turned on, the lift arms will lower to a preset height above the ground.
Location of the Float Sequence Valve
(15) Float sequence valve.
Float sequence valve (15) is mounted on the left side of the front frame in front of and above the main control valve.
When the hydraulic control lever is moved past the LOWER position to the FLOAT position, float sequence valve (15) is activated. Float sequence valve (15) is used to move the lift spool in the main control valve to the FLOAT position. In the float position, both the rod end and head end of the lift cylinders are open to tank.
Pilot Hydraulic System
SMCS Code: 5050-PS
Schematic of the Pilot Hydraulic System
(1), (4) Line to lift section of main control valve. (2), (3) Line to tilt section of main control valve. (5) Vent line to main control valve. (6) Pilot oil return. (7) Float sequence valve. (8) Lift arm positioner valve. (9) Line and orifice. (10) Manifold. (11) Pilot control valve. (12) Pilot oil return. (13) Lift (raise) valve stem. (14) Lower valve stem. (15) Dump valve stem. (16) Tilt back (crowd) valve stem. (17) Pilot oil supply.
Pilot control valve (11) is operated manually by the operator. The pilot control valve sends low pressure oil to operate the lift and tilt valve spools.
The tilt and lift valve spools control the operation of the tilt and lift cylinders. Oil lines (1), (2), (3) and (4) connect the output of the pilot control valve to the pilot inlets on the main control valve.
Location of the Hydraulic Control Lever
(18) Hydraulic control lever.
Pilot control valve (11) uses only one control lever (joystick type) to control the operations of both lift and tilt functions. Hydraulic control lever (18) is connected to a pivot plate that contacts the four plungers for raise, lower, dump and tilt back positions.
When hydraulic control lever (18) is moved to a position, oil flows from the pilot control valve to the main control valve. This causes the spool in the main control valve to move. Movement of the spool opens the passage for implement oil flow to the tilt or lift cylinders.
The pilot control valve section for tilt control has three positions; TILT BACK, HOLD and DUMP. The pilot control valve section for lift control has four positions; RAISE, HOLD, LOWER and FLOAT. The oil cannot flow through the valve when it is in the HOLD position because it is a closed center valve.
Pilot Control Valve
SMCS Code: 5059
Pilot Control Valve (TILT BACK Position)
(1) Control lever. (2) Plate. (3) Rod. (4) Rod. (5) Seat. (6) Metering spring. (7) Spring. (8) Return chamber. (9) Return passage. (10) Return passage. (11) Passage. (12) Passage. (13) Spool. (14) Spool. (15) Port. (16) Passage. (17) Port. (18) Line from the main control valve. (19) Line to the main control valve. (20) Pilot pump.
When control lever (1) is moved to the left, plate (2) tilts to the left. Plate (2) pushes down on rod (3) and seat (5) pushes against the force of metering spring (6) and spring (7). The force of metering spring (6) moves spool (14) down, opening passage (11). The pilot pump ol can now go through passages (16) and (11) and out port (15) through line (19) to the main control valve. The pressure oil on the end of the main control valve stem causes it to move for implement operation.
The oil at the opposite end of the main control valve stem (for the operation) flows back through port (17), through return passage (10) and into return chamber (8) back to the hydraulic tank.
As long as rod (4) is not pushed down, return passage (10) is open and passage (12) is closed.
Spring (7) provides the necessary force to allow the control lever to return to the HOLD position when released.
When the control lever is moved, metering spring (6) is compressed, moving spool (14). The spool controls the pressure of the pilot oil that goes through passage (11) to the main control valve. The pilot oil pressure sent to the main control valve increases, directly proportional to the travel distance of the control lever. Movement of the main control valve stem causes an increased oil flow to the cylinders, proportional to an increased pilot oil pressure. Fine movement of the control lever allows fine control operation of the cylinders.
Modulated Pilot Pressure
Partial Cross Section of the Pilot Control Valve
(3) Rod. (5) Seat. (6) Metering spring. (7) Spring. (9) Return passage. (11) Passage. (14) Spool. (16) Passage. (21) Passage. (D) Diameter [of spool (14) for return passage (9)]. (d) Diameter [of spool (14) for return passage (11)]. (E) Shoulder [of spool (14)]. (F) Shoulder [of spool (14)]. (L) Length [of spring (6) under compression].
When the control lever is moved to the left, rod (3) compresses metering spring (6) through seat (5), moving spool (14) down. Any movement of spool (14), under this condition, controls the pressure of the pilot oil that goes through passage (11) to the main control valve. This allows modulation (up and down) of the pilot pressure to the stem of the main control valve for inching operation of the implement system.
NOTE: See Figure A.
When the force of metering spring (6) moves spool (14) down, passage (11) opens. Part of the pilot oil can flow through passage (21) and out to the main control valve, moving the stem only part of its travel distance against the force of its spring. This causes a slight increase in pressure which works against shoulders (E) and (F) of spool (14). Because the area of shoulder (E) is larger than that of shoulder (F), spool (14) moves up a small amount of its travel distance against the force of metering spring (6). Return passage (9) partially opens and passage (11) is closed (see Figure B).
Part of the oil in passage (21) goes out through return passage (9) causing a slight decrease in oil pressure in passage (21). When the oil pressure acting on spool (14) is less than the force of metering spring (6), spool (14) returns to its position in Figure A.
Spool (14) modulates (shifts up and down) in a balanced condition between the pressure in passage (21) and the force of metering spring (6).
During modulation (up-and-down movement) of spool (14), a condition can occur that both return passages (9) and (11) are closed at the same time (see Figure C). This condition provides a certain length (L) of metering spring (6). At this point, the pressure in passage (21) and the force of metering spring (6) are equal.
Further downward movement of rod (3) decreases length (L) of metering spring (6) and establishes a new balance between the force of metering spring (6) and the pressure in passage (21). The pressure in passage (21) increases with an increase in the force of metering spring (6).
Pilot oil pressure sent to the main control valve from the pilot control valve increases, directly proportional to the travel distance of the control lever.
Movement of the main control valve stem causes an increased oil flow to the cylinders, proportional to an increased pilot pressure. Fine movement of the pilot control valve lever allows fine control of operation of the cylinders.
Selector and Pressure Control Valve
SMCS Code: 5072
Location of the Selector and Pressure Control Valve
The selector and pressure control valve is part of the pilot oil system. It sends oil to the pilot control valve. The selector and pressure control valve makes pressure oil available to the pilot control valve to lower a raised bucket (lift arms) when the engine is off.
Selector and Pressure Control Valve
(1) Drain passage. (2) Spacers. (3) Spring. (4) Holes (four). (5) Inlet passage from head end of tilt cylinders. (6) Valve spool. (7) Holes (two). (8) Inlet passage from pilot pump section.
During normal operation with the engine running, the pilot pump oil enters the selector and pressure control valve through inlet passage (8). The pressure of the oil entering inlet passage (8) is controlled by the pilot oil pressure reducing valve. The oil also flows from passage (8) to the pilot control valve (joystick).
The oil is blocked at the pilot control valve causing the pilot pump oil pressure to increase. The oil pressure increases in the valve center. The higher oil pressure moves valve spool (6) to the left against spring (3). Moving the valve spool to the left covers orifice (7). Oil in lift cylinder inlet passage (5) is blocked by valve spool (6) and cannot enter the pilot system.
When the bucket is in the air and the engine is stopped, no pilot pump oil is sent to inlet passage (8). Spring (3) moves valve spool (6) to the right. Holes (7) in valve spool (6) allow high pressure oil from the lift cylinders to enter the pilot system. Valve spool (6) also controls the pressure of the oil from inlet passage (5) to the pilot control valve.
When the pressure through passage (8) gets too high, the pressure will cause valve spool (6) to move against the force of spring (3). This decreases the flow of oil through holes (7) in the valve spool and decreases the pressure in passage (8).
When the pilot control valve is moved to the LOWER position, pilot oil is sent to move the lift control spool. The lift control spool directs the oil in the lift cylinder back to the tank allowing the bucket to be lowered.
A check valve in the line from inlet passage (8) will not let oil go to the pilot pump section.
NOTE: When the engine is stopped and the lift arms are raised, the bucket can also be dumped.
Check Valves
SMCS Code: 5067
Location of the Check Valves
(1) Brake and pilot check valve.
Location of the Check Valves (Shown with the Transmission Removed)
(2) Pilot oil pressure check valve. (3) Head end of lift cylinders check valve. (4) Selector and pressure control valve.
There are three one-way check valves in the implement hydraulic system. These valves permit the flow of oil in one direction only. Check valve (1) is in the brake and pilot oil pump supply line. Check valve (2) is in the line from the pilot oil pressure reducing valve to selector and pressure control valve (4). Check valve (3) is in the line betweent he head end of the lift cylinders and selector and pressure control valve (4).
During normal operation, brake and pilot check valve (1) opens and lets pilot pressure oil flow to the braking system and the pilot pressure reducing valve. Check valve (1) will not let pilot pressure oil or braking system oil return to the brake and pilot pump.
During normal operation, check valve (2) opens and lets pilot pressure oil go to selector and pressure control valve (4) for operation of the pilot valves. When the engine is stopped and the lift arms are raised, check valve (2) will not allow the oil from the head end of the lift cylinders to flow to the brake and pilot pump section.
During normal operation, check valve (3) will not allow pilot pressure oil to flow into the head end of the lift cylinders. When the engine is stopped and the lift arms are raised, check valve (3) will permit pressure oil from the head end of the lift cylinders to flow to selector and pressure control valve (4) for operation of the pilot valves.
Components of a Check Valve
(5) Inlet passage. (6) Valve. (7) Spring. (8) Holes. (9) Outlet passage.
Pressure oil at inlet passage (5) pushes valve (6) against spring (7). The oil is then free to go through holes (8) in valve (6) and outlet passage (9). Pressure oil at outlet passage (9) pushes against valve (6) and holds it closed. No oil can flow through the check valve.
Lift Arm Positioner Control
SMCS Code: 5112
The lift arm positioner group returns the lift arms to a preset height when the lift arms are lowered. The lift arm positioner circuit is made up of lift arm positioner switch (1), magnetic switch (2), magnet (3) and lift arm positioner valve (4).
Operator's Station
(1) Lift arm positioner switch.
When lift arm positioner switch (1) is in the ON position, power is supplied to magnetic switch (2).
Lift Arm Assembly
(2) Magnetic switch. (3) Magnet.
When the hydraulic control lever is moved to the LOWER position, the lift arms move downward. Magnetic switch (2) is located on the lift arm. As the lift arm moves downward with the bucket, magnetic switch (2) passes magnet (3). This causes the magnetic switch to close.
Left Side View of the Transmission Compartment
(4) Lift arm positioner valve.
When magnetic switch (2) closes, power is supplied to lift arm positioner valve (4). This causes the lift arm positioner valve to close.
Lift arm positioner valve (4) controls the flow of pilot oil to and from the lift control valve spool. When the lift arm positioner valve closes, pilot oil from the lift control valve spool is sent to tank through an orifice. This causes the lift control valve spool to gradually return to center. The lift arms and bucket will come to a controlled stop.
The height at which the lift arms and bucket comes to rest can be varied by adjusting the position of magnetic switch (2). Moving the magnetic switch upwards will raise the lift arm and bucket height. Moving the magnetic switch downwards will lower the lift arm and bucket height.
Pressure Reducing Valve (Pilot Hydraulic System)
SMCS Code: 5467-PS
Location of Pilot Oil Pressure Reducing Valve
(1) Pilot oil pressure reducing valve.
The pilot oil pressure is controlled by pilot oil pressure reducing valve (1). The pilot oil system will constantly operate at the pressure reducing valve pressure setting.
Pilot Oil Pressure Reducing Valve
(1) Valve. (2) Drain outlet. (3) Inlet. (4) Reduced pressure outlet.
Pilot oil from the brake and pilot pump enters the pilot oil pressure reducing valve through inlet (3). Pilot oil pressure reducing valve (1) is a cartridge type valve that maintains pilot pressure at 3515 ± 70 kPa (510 ± 10 psi).
Reduced pressure oil flows to the selector and pressure control valve through outlet (4). Excess oil returns to the hydraulic tank through outlet (2).
Main Hydraulic System
SMCS Code: 5050
Schematic of the Hydraulic System
(1) Tilt cylinder. (2) Lift cylinders. (3) Main control valve. (4) Autodig pressure sensor connection ports. (5) Tilt cylinder rod end line relief valve. (6) Tilt cylinder head end line relief valve. (7) Tilt control valve spool. (8) Lift control valve spool. (9) Lift circuit relief valve. (10) Main relief valve. (11) Lift arm positioner valve. (12) Float sequence valve. (13) Breaker relief valve. (14) Hydraulic filter group. (15) Hydraulic tank. (16) Pilot control valve. (17) Manifolds. (18) Check valves. (19) Pilot oil pressure reducing valve. (20) Selector and pressure control valve. (21) Main implement pump. (22) Torque converter scavenge pump. (23) Brake and pilot pump. (24) Steering pump. (AA) Pressure test point for rod end of tilt cylinder. (BB) Pressure test point for head end of tilt cylinder. (CC) Pressure test point for main hydraulic system.
Tilt Circuit
TILT BACK Operation
When the engine is running with the hydraulic control lever in the HOLD position, brake and pilot pump (23) takes oil from hydraulic tank (15) and sends it through a check valve to pilot oil pressure reducing valve (19) and the braking system. Pilot oil pressure reducing valve (19) maintains a constant pressure in the pilot system. The pilot oil then flows through a check valve to selector and pressure control valve (20) and pilot control valve (16). The valve stems in the pilot valve stop the flow of oil through the valve in the HOLD position. Excess oil flows from pilot oil pressure reducing valve (19) and returns to hydraulic tank (15) through filter group (14).
At the same time, steering pump (24) sends oil to the steering control valve of the steering system. Also, main implement pump (21) sends oil to main relief valve (10) which controls the maximum pressure in the implement oil system.
With both valve spools of main control valve (3) in their HOLD positions, oil flows through the main control valve, through oil filter group (14) and back into hydraulic tank (15). If the oil filters get full of foreign material (debris), the filter bypass valve (in the filter group) will open and let the return oil go directly into the hydraulic tank.
When the hydraulic control lever is moved to the TILT BACK position, the pilot valve tilt back stem moves to the TILT BACK position. Pilot oil is now free to go through pilot control valve (16) to the tilt back end of tilt control valve spool (7). This causes the tilt control valve spool to move. The pilot oil at the dump end of tilt control valve spool (7) goes back to pilot control valve (16), through the pilot valve dump stem and on to hydraulic tank (15).
The movement of tilt control valve spool (7) stops the flow of oil through main control valve (3). Implement pump pressure increases and opens the load check valve. The oil from implement pump (21) now goes to the head end of tilt cylinder (1) and causes the cylinder rod to extend. The Z-bar linkage causes the bucket to tilt back. The movement of the cylinder piston and rod pushes the oil out of the rod end of the tilt cylinder. This oil comes into main control valve (3) and goes around both control valve spools (7) and (8) on its way back to oil filter group (14) and hydraulic tank (15).
When the hydraulic control lever is released, the lever and dump stem return to the HOLD position causing the flow of pilot oil to be stopped. The spring on tilt valve spool (7) moves the valve spool back to the HOLD position. The pilot oil at the tilt back end of the tilt control valve spool goes back to pilot control valve (16), through the tilt back stem and on to hydraulic tank (15).
The implement oil in tilt cylinder (1) is held by tilt valve spool (7) and movement of the cylinder piston and rods stops. The bucket will stay at that angle until the hydraulic control lever is moved again.
DUMP Operation
When the hydraulic control lever is moved to the DUMP position, the pilot valve dump stem moves to the DUMP position. Pilot oil is now free to flow through pilot control valve (16) to the dump end of tilt valve spool (7). This causes tilt spool (7) to move. The pilot oil at the tilt back end of tilt spool (7) goes back to the tilt back stem of pilot control valve (16) and on to hydraulic tank (15).
The movement of tilt spool (7) stops the flow of oil through main control valve (3). Implement pump pressure increases and opens the load check valve. The oil from main implement pump (21) now goes to the rod end of tilt cylinder (1) and causes the cylinder rod to retract. The Z-bar linkage causes the bucket to dump.
The movement of the cylinder piston and rod pushes the oil out of the head end of the tilt cylinder. This oil comes into main control valve (3) and goes around both valve spools (7) and (8) on its way back to oil filter group (14) and hydraulic tank (15).
When the hydraulic control lever is released, the lever and dump stem return to the HOLD position causing the flow of pilot oil to be stopped. The spring on tilt spool (7) moves the valve spool back to the HOLD position. The pilot oil at the dump end of the tilt valve spool goes back to the dump stem in pilot control valve (16) and on to hydraulic tank (15).
The implement oil in tilt cylinder (1) is held by tilt spool (7) and movement of the cylinder piston and rod stops. The bucket is held in the dumped position until the control lever is moved again.
DUMP Operation with Stopped Engine
When the lift arms are raised, the bucket can be dumped while the engine is stopped. The pilot oil supply comes from the head end of the lift cylinders. This oil goes through a check valve to selector and pressure control valve (20) which decreases the pressure of the oil to pilot oil pressure. The oil then goes to pilot control valve (16). When the hydraulic control lever is moved to the DUMP position, the oil goes to tilt valve spool (7) and moves it to the DUMP position. The head end of tilt cylinder (1) is now open to hydraulic tank (15). The makeup valve in main control valve (3) opens so that the rod end of tilt cylinder (1) is also open to hydraulic tank (15). The weight of the bucket causes the bucket to dump.
Lift Circuit
RAISE Operation
When the engine is running with the hydraulic control lever in the HOLD position, brake and pilot pump (23) takes oil from hydraulic tank (15) and sends it through a check valve to pilot oil pressure reducing valve (19) and the braking system. Pilot oil pressure reducing valve (19) maintains a constant pressure in the pilot system. The pilot oil then flows through a check valve to selector and pressure control valve (20) and pilot control valve (16). The valve stems in the pilot control valve stop the flow of oil through the valve in the HOLD position. Excess oil flows from pilot oil pressure reducing valve (19) and returns to hydraulic tank (15) through filter group (14).
Main implement pump (21) sends oil through main control valve (3) because both valve spools are in their HOLD positions. The oil then goes through oil filter group (14) and back into hydraulic tank (15).
When the hydraulic control lever is moved to the RAISE position, the lift stem in pilot control valve (16) moves to the RAISE position. Pilot oil is now free to go through pilot control valve (16) to the lift end of lift spool (8). This causes the lift valve spool to move. The pilot oil at the lower end of lift valve spool (8) goes back to the lower stem in pilot control valve (16) and on to hydraulic tank (15).
The movement of lift valve spool (8) stops the flow of oil through main control valve (3). The main implement pump pressure increases and opens the load check valve in main control valve (3). The oil from main implement pump (21) now goes to the head end of lift cylinders (2) and causes the cylinder rods to extend. The lift arms cause the bucket to lift.
The movement of the cylinder pistons and rods pushes the oil out of the rod end of the lift cylinders. This oil comes into main control valve (3) and goes around lift spool (8) on its way back to oil filter group (14) and hydraulic tank (15).
When the hydraulic control lever is released, the lever and dump stem return to the HOLD position causing the flow of pilot oil to be stopped. The spring on lift valve spool (8) moves the valve spool back to the HOLD position. The pilot oil at the lift end of the lift spool goes back through pilot control valve (16) and on to hydraulic tank (15). The implement oil in lift cylinders (2) is held by lift spool (8) and movement of the cylinder pistons and rods stops. The lift arms and bucket are held until the hydraulic control lever is moved again.
LOWER Operation
When the hydraulic control lever is moved to the LOWER position, the lower stem moves to the LOWER position. Pilot oil is now free to go through pilot control valve (16) to the lower end of lift spool (8). This causes the lift spool to move. The pilot oil at the lift end of lift spool (8) goes back to the pilot control valve lift stem and on to hydraulic tank (15).
The movement of lift spool (8) stops the flow of oil through main control valve (3). The main implement pump pressure increases and opens the load check valve. The oil from main implement pump (21) now goes to the rod end of lift cylinders (2) and causes the cylinder rods to retract. The lift arms cause the bucket to lower. The movement of the cylinder pistons and rods pushes the oil out of the head end of the lift cylinders. This oil comes into main control valve (3) and goes around lift spool (8) on its way back to oil filter group (14) and hydraulic tank (15).
When the hydraulic control lever is released, the lever and the lower stem go back to the HOLD position. The flow of pilot oil through pilot control valve (16) is stopped. The springs on lift spool (8) move the valve spool back to the HOLD position. The pilot oil at the lower end of the lift valve spool goes back to pilot control valve (16) and on to hydraulic tank (15). The implement oil in lift cylinders (2) is held by lift spool (8) and movement of the cylinder pistons and rods stops. The bucket is held in the lowered position until the hydraulic control lever is moved again.
FLOAT Operation
When the hydraulic control lever is moved to the FLOAT position, the pilot valve lower stem moves to the FLOAT position. The flow of oil to lift spool (8) is the same as in the LOWER position. The extra movement of the lower stem allows greater pilot pump oil pressure into the line to the lift control valve spool. This pressure is also felt in float sequence valve (12). This pressure moves the spool in float sequence valve (12), which allows oil in the spring chamber of the makeup valve in the main control valve to vent (drain) to tank. This permits the makeup valve to open and lets implement oil go directly to hydraulic tank (15). The head end and rod end of lift cylinders (2) are also open to the hydraulic tank. Outside forces on the bucket will control the movement of the cylinder pistons and rods.
When the hydraulic control lever is released it will return to the HOLD position.
LOWER Operation with Stopped Engine
The bucket can be lowered while the engine is stopped. The pilot oil supply comes from the head end of the lift cylinders. This oil goes through the check valve to selector and pressure control valve (20) which decreases the pressure of the oil to pilot oil pressure. The oil then goes to pilot control valve (16). When the hydraulic control lever is moved to the LOWER and on to the FLOAT position, the lower stem moves to the FLOAT position. Pilot oil goes to lift spool (8) and moves it to the LOWER position. The head end of lift cylinders (2) is now open to hydraulic tank (15). The makeup valve in main control valve (3) is vented so it opens and the rod ends of lift cylinders (2) are open to hydraulic tank (15). The weight of the bucket and lift arms causes the bucket to lower to the ground.
NOTE: When the engine is stopped and the lift arms are raised, the bucket can also be dumped.
Main Control Valve
SMCS Code: 5051-MV
Tilt Valve Spool
Main Control Valve (Tilt Valve Spool in the TILT BACK Position and Lift Valve Spool in the HOLD Position)
(1) Chamber for pilot oil. (2) Springs. (3) Spring. (4) Makeup valve for rod end of tilt cylinders. (5) Passage to rod end of tilt cylinder. (6) Passage to head end of tilt cylinder. (7) Passage. (8) Spring. (9) Load check valve for tilt circuit. (10) Inlet passage for implement oil. (11) Tilt valve spool. (12) Chamber for pilot oil. (13) Passage. (14) Passage. (15) Outlet passage to hydraulic tank. (16) Lift valve spool.
Oil from the implement pump section goes through inlet passage (10) to tilt valve spool (11). The tilt valve spool is a spring-centered, open center, pilot operated spool with three positions: TILT BACK, HOLD and DUMP. Springs (2) keep the spool in the HOLD position when there is no pilot pressure oil in chamber (1) or (12). Movement of the spool is controlled by pilot pressure oil from the pilot control valve in chamber (1) or (12).
When tilt valve spool (11) is in the HOLD position, implement oil goes from inlet passage (10), through passage (14) and outlet passage (15) to the hydraulic tank. The position of the spool holds (blocks) the oil in both ends of the tilt cylinder and stops the movement of the cylinder.
TILT BACK Operation
When the hydraulic control lever is moved to the TILT BACK position, pilot oil is sent to chamber (1) and tilt valve spool (11) moves to the right. Implement oil is sent from inlet passage (10) to load check valve (9). The load check valve prevents reverse oil flow which can cause cylinder drift or load loss. Load check valve (9) does not open until the oil pressure becomes greater than the force of spring (8) and the head end pressure of the tilt cylinder. The oil opens the load check valve, goes through passage (7) and out passage (6) to the head end of the tilt cylinder. This causes the bucket to tilt back.
Oil from the rod end of the tilt cylinder comes through passage (5), around tilt valve spool (11), through passage (13), around lift valve spool (16) and through outlet passage (15) to the hydraulic tank. In this way, the oil from the rod end of the tilt cylinder bypasses the lift circuit and prevents TILT BACK and RAISE operations at the same time.
NOTE: When tilt valve spool (11) is fully in the TILT BACK position, no implement oil goes to lift valve spool (16). The lift circuit will not operate.
DUMP Operation
When the hydraulic control lever is moved to the DUMP position, pilot oil goes to chamber (12) and tilt valve spool (11) moves to the left. Oil flow to the tilt cylinder in the DUMP position is the reverse of oil flow in the TILT BACK position. Implement oil is sent from inlet passage (10) to load check valve (9). The load check valve opens when inlet pressure becomes greater than the force of spring (8) and the rod end pressure of the tilt cylinder. The oil now goes through passage (7) and out passage (5) to the rod end of the tilt cylinder. This causes the bucket to dump. During this operation, when the tilt cylinder rod retracts faster than the pump can provide oil to the rod end, makeup valve (4) moves against spring (3) and permits oil from the tank to add to the implement oil. This prevents cavitation (vacuum) in the system.
Oil from the head end of the tilt cylinder comes through passage (6), goes around tilt valve spool (11), lift valve spool (16) and through outlet passage (15) to the hydraulic tank. The oil from the head end of the tilt cylinder also bypasses the lift circuit and prevents DUMP and RAISE operations at the same time.
NOTE: When tilt valve spool (11) is fully in the DUMP position, no implement oil goes to lift valve spool (16). The lift circuit will not operate.
Lift Valve Spool
Main Control Valve (Lift Valve Spool in the RAISE Position and Tilt Valve Spool in the HOLD Position)
(10) Inlet passage for implement oil. (11) Tilt valve spool. (13) Passage. (14) Passage. (15) Outlet passage to hydraulic tank. (16) Lift valve spool. (17) Chamber for pilot oil. (18) Springs. (19) Makeup valve for rod end of lift cylinders. (20) Vent passage to float sequence valve. (21) Spring. (22) Passage to rod end of lift cylinders. (23) Passage to head end of lift cylinders. (24) Passage. (25) Load check valve for lift circuit. (26) Spring. (27) Chamber for pilot oil.
Oil from the implement pump section goes through inlet passage (10) around tilt valve spool (11) before it goes to lift valve spool (16). The lift valve spool is a spring-centered, open center, pilot operated spool with three positions: RAISE, HOLD and LOWER. Makeup valve (19) provides the FLOAT operation of the lift circuit. Springs (18) keep lift valve spool (16) in the HOLD position when there is no pilot pressure oil in chamber (17) or (27). Movement of the spool is controlled by pilot pressure oil from the pilot control valve in chamber (17) or (27).
When lift valve spool (16) is in the HOLD position, implement oil goes from inlet passage (10), through passage (14) and outlet passage (15) to the hydraulic tank. The position of the spool holds (blocks) the oil in both ends of the lift cylinders and prevents the cylinders from moving.
RAISE Operation
When the hydraulic control lever is moved to the RAISE position, pilot oil is sent to chamber (17) and lift valve spool (16) moves to the right. Implement oil is sent from inlet passage (10) to load check valve (25). The load check valve does not open until the oil pressure becomes greater than the force of spring (26) and the head end pressure of the lift cylinders. The oil opens load check valve (25), goes through passage (24) and out passage (23) to the head end of the lift cylinders. This causes the bucket (lift arms) to raise.
Oil from the rod end of the lift cylinders comes through passage (22), goes around lift valve spool (16), through passage (13) and outlet passage (15) to the hydraulic tank.
Main Control Valve (Tilt Valve Spool in the HOLD Position, Lift Valve Spool in the LOWER Position and Makeup Valve in the FLOAT Position)
(10) Inlet passage for implement oil. (11) Tilt valve spool. (13) Passage. (14) Passage. (15) Outlet passage to hydraulic tank. (16) Lift valve spool. (17) Chamber for pilot oil. (18) Springs. (19) Makeup valve for rod end of lift cylinders. (20) Vent passage to float sequence valve. (21) Spring. (22) Passage to rod end of lift cylinders. (23) Passage to head end of lift cylinders. (24) Passage. (25) Load check valve for lift circuit. (26) Spring. (27) Chamber for pilot oil.
LOWER Operation
When the hydraulic control lever is moved to the LOWER position, pilot oil goes to chamber (27) and lift valve spool (16) moves to the left. Oil flow to the lift cylinders is now the reverse of oil flow in the RAISE position. Implement oil is sent from inlet passage (10) to load check valve (25). The load check valve opens when inlet pressure becomes greater than the force of spring (26) and the rod end pressure of the lift cylinders. The oil now goes through passage (24) and out passage (22) to the rod end of the lift cylinders. This causes the bucket (lift arms) to lower.
During this operation when the lift cylinder rods retract faster than the pump can provide oil to the rod ends, makeup valve (19) moves against spring (21) and the pressure of the oil in vent passage (20). This permits oil from the tank to add to the implement oil and prevents cavitation (vacuum) in the system.
Oil from the head end of the lift cylinders comes through passage (23), goes around lift valve spool (16) and through outlet passage (15) to the hydraulic tank.
FLOAT Operation
When the hydraulic control lever is moved to the FLOAT position, the movement of lift valve spool (16) is the same as in the LOWER position. The float sequence valve opens vent passage (20) to a tank passage and makeup valve (19) is free to open. Implement oil pressure holds the makeup valve open. The pump oil from passage (24) and the oil in passage (22) now go through passage (13) and outlet passage (15) to the hydraulic tank. The lift cylinders can now move freely in either direction according to the amount and direction of force on the bucket. As the cylinder rods move, all extra oil goes out passage (15) to the hydraulic tank and pump oil comes in from inlet passage (10).
Load Check Valves
Load check valves (9) and (25) prevent reverse oil flow in the cylinders (tilt and lift), which can cause cylinder drift. For example, when the tilt valve spool is in the TILT BACK position, pump oil opens load check valve (9) and goes through passages (6) and (7) to the head end of the tilt cylinder. If the pressure at inlet passage (10) decreases, the pressure of the oil, along with spring (8) will close load check valve (9) and hold the oil in the head end of the tilt cylinder. This prevents any movement of the tilt cylinder and will not permit the bucket to dump.
Makeup Valves
There are two makeup valves in the main control valve. Makeup valve (19) is in the rod end of the lift circuit and makeup valve (4) is in the rod end of the tilt circuit.
The makeup valves will permit oil from the return line to add with pump oil when the cylinder rods are retracted faster than the pump can supply oil to the cylinders. The makeup valves make sure that there is enough oil available so that there is no cavitation (vacuum) in the cylinders.
Makeup valve (4) operates when the rod end of the tilt cylinder is retracted fast when the bucket is dumped. When the pressure in passage (5) decreases enough, the pressure in passage (13) will become greater than the force of spring (3). Makeup valve (4) will move up and oil from passage (13) will go into passage (5) and add to the oil in the rod end of the tilt cylinder. Makeup valve (4) will operate in the same way when an outside force on the bucket causes the tilt cylinder to be retracted.
During the LOWER operation, makeup valve (19) operates the same way as makeup valve (4). During FLOAT operation, makeup valve (19) provides the float operation of the lift circuit (see "FLOAT Operation").
Relief Valves
SMCS Code: 5069; 5117-L9; 5117-LQ
Location of the Relief Valves
(1) Main relief valve. (2) Tilt cylinder rod end line relief valve. (3) Tilt cylinder head end line relief valve.
Location of the Lift Circuit Relief Valve
(4) Lift circuit relief valve.
The main control valve is equipped with four relief valves; main relief valve (1), tilt cylinder rod end line relief valve (2), tilt cylinder head end line relief valve (3) and lift circuit relief valve (4).
Main Relief Valve
Main Relief Valve
(1) Oil inlet opening. (2) Valve. (3) Pilot valve. (4) Locknut. (5) Plunger. (6) Oil outlet opening. (7) Passage. (8) Spring. (9) Pin. (10) Spacer.
The main relief valve is in front of all other valves in the implement hydraulic system. It is a pilot-operated, cartridge-type valve. The pressure setting of the main relief valve is 20 685 ± 170 kPa (3000 ± 25 psi).
Implement system oil flows into inlet opening (1), through the orifice in the center of valve (2) and into the chamber for spring (8). The oil in the spring chamber contacts pilot valve (3). When the pressure of the oil in the circuit is less than the setting of the relief valve, the force of the pilot valve spring keeps it closed.
If the pressure of the oil through inlet opening (1) and in the chamber for spring (8) gets as high as the setting of the relief valve, the oil overcomes spring (9) tension and moves pilot valve (3). When the pilot valve opens, the oil in the spring chamber flows past the open pilot valve and through passage (7) to the tank.
With only the pilot valve open, the force of spring (8) is acting on valve (2). The pressure of the oil in inlet opening (1) moves valve (2) far enough to allow implement oil to flow through the inlet opening and through outlet openings (6) back to the hydraulic tank. The pressure of the oil can not increase to a pressure higher than the setting of the relief valve.
The pressure setting of the relief valve can be changed by either an increase or decrease in the force of spring (9) that keeps pilot valve (3) closed. Loosen locknut (4) and turn plunger (5) clockwise for an increase or counterclockwise for a decrease in the pressure setting of the relief valve.
Line Relief Valves
Reference: For the pressure setting of the line relief valves, refer to Specifications, "Relief Valve (Line)" for the machine that is being serviced.
Line Relief Valve
(1) Valve body. (2) Nut. (3) Spring.
The head end and rod end of the tilt cylinder each has its own relief valve. The construction and operation of these valves is the same. The operation of these valves is similar to the main relief valve, however, their construction is different.
When the tilt valve spool is in the HOLD position, the relief valve in the head end and rod end of the tilt cylinder limits the maximum amount of pressure in the cylinder lines.
If an outside force on the bucket causes pressure to become too high, the relief valve will permit movement of the cylinder piston. This prevents damage to the machine components.
The relief valve for the rod end of the tilt cylinder also releases the rod end pressure when the lift arms are lifted with the bucket fully dumped and the tilt control valve spool is in the HOLD position.
Lift Circuit Relief Valve
Lift Circuit Relief Valve
(1) Oil outlet port. (2) Oil inlet port.
The lift circuit relief valve limits the hydraulic pressure in the head end of the lift cylinders when the lift spool of the main control valve is in the HOLD position.
If an outside force on the lift cylinders causes oil pressure to become too high, the relief valve opens, permitting movement of the cylinders and allowing high pressure oil to return to the hydraulic tank. This prevents damage to the machine components.
The operation of the lift circuit relief valve is similar to the main relief valve, however the construction is different.
Bucket Control
SMCS Code: 6107
Bucket Control Group (Typical)
(1) Tilt link. (2) Tilt lever. (3) Tilt cylinder. (4) Lift cylinders. (5) Lift arm assembly. (6) Bucket.
The bucket control group gives a way to control the operation of bucket (6). This group is made up of: two lift cylinders (4), one tilt cylinder (3), lift arm assembly (5), tilt lever (2) and tilt link (1). This type of linkage is known as a Z-bar linkage because of the Z formed by the tilt cylinder, tilt lever and tilt link. Tilt cylinder (3), lift cylinders (4) and lift arm assembly (5) are fastened to the loader frame by pins.
When pressure oil is sent to the head end of the lift cylinders, lift arm assembly (5) is lifted. When pressure oil goes to the rod end of lift cylinders (4), the lift arm assembly is lowered.
The bucket will tilt back when pressure oil is sent to the head end of tilt cylinder (3). The bucket will dump when pressure oil goes to the rod end of the tilt cylinder.
Ride Control System
SMCS Code: 5050-R6
Schematic of the Ride Control System
(1) Lift cylinders. (2) Ride control accumulator. (3) Main control valve. (4) Orifice. (5) Check valve. (6) Solenoid valve. (7) Ride control relief valve. (8) Ride control diverter valve. (9) Lift control valve spool. (10) Lift circuit relief valve. (11) Hydraulic tank. (12) Selector and pressure control valve. (13) Brake and pilot pump. (AA) Pressure test point for rod end of tilt cylinder. (BB) Pressure test point for head end of tilt cylinder. (CC) Pressure test point for main hydraulic system.
The optional ride control system provides a means for dampening the bucket forces which produce a pitching motion as the machine travels over rough terrain.
The main components of the ride control system are solenoid valve (6), ride control relief valve (7), ride control diverter valve (8), lift cylinders (1), orifice (4) and ride control accumulator (2).
Location of the Ride Control Diverter Valve
(6) Solenoid valve. (8) Ride control diverter valve.
Solenoid valve (6) and ride control diverter valve (8) are located on the front frame of the machine above and forward of the main control valve.
Location of the Ride Control Accumulator
(2) Ride control accumulator.
Ride control accumulator (2) is mounted in the front frame near the articulation hitch.
Location of the Ride Control Switch
(14) Ride control switch. (15) Ride control indicator.
Ride control switch (14) is mounted in the control panel in the operator's station. Ride control indicator (15) is located on the indicator panel in the operator's station.
When the ride control system is ON, the head end of the lift cylinders is connected with ride control accumulator (2). The accumulator provides a cushioning effect to the head end oil, allowing the lift cylinders to extend and retract slightly. The bucket can move as a balance weight against the movement of the machine.
Ride control switch (14) has three positions: OFF, ON and AUTO. When turned to ON, the ride control system will remain on at all times. When turned to AUTO, the ride control system will automatically turn on when the machine ground speed exceeds 5 km/h (3 mph). Ride control indicator (15) will illuminate when the ride control system is activated.
Solenoid valve (6) is a normally closed valve. When lift spool (9) in main control valve (3) is in the HOLD position and the switch in the operator panel is in the OFF position, the coil in the solenoid is not energized. A spring in solenoid valve (6) holds the spool up. With the solenoid valve spool in this position, pilot oil flow from the pilot hydraulic system is blocked.
When the ride control system is turned OFF, orifice (4) between lift cylinders (1) and accumulator (2) allows a continual sensing of the lift cylinder pressure. When a load is in the bucket, pressure increases in the head end of the lift cylinders. This pressure passes through the orifice into the accumulator to compress the nitrogen charge. This prevents the lift arms from moving dangerously when the ride control system is reactivated.
When lift spool (9) is in the HOLD position and switch (14) on the operator panel is moved to the ON position, the coil in the solenoid valve is energized. When the coil is energized it causes the spool inside the valve to overcome spring tension and move down. When the spool moves down it opens a path for pilot oil from the pilot hydraulic system to flow into diverter valve (8).
The pilot oil flows through the solenoid valve, into the diverter valve and causes the spool inside the diverter valve to shift to the left. Head end oil flows into accumulator (2). Rod end oil flows back to hydraulic tank (11).
As the machine moves across rough terrain with a loaded bucket, the forces of the load act against the lift cylinders. When the load acts against the head end of the cylinders, that oil flows into the accumulator.
The accumulator has a nitrogen precharge that resists the oil flow and acts as a shock absorber. Rod end make up oil can flow through the diverter valve into the cylinders.
Location of the Ride Control Relief Valve
(7) Ride control relief valve.
Ride control relief valve (7) protects the ride control accumulator and ride control components from high pressure spikes.
Reference: For more information on operating the ride control system, refer to Operation and Maintenance Manual for the machine that is being serviced.