Note: Illustration 1 shows the machine with the 3rd function (option) and the ride control option. Not all machines will have this option.
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| Illustration 1 | g01518016 |
(1) Valve manifold (inlet) (2) Control valve (tilt) (3) Control valve (lift) (4) Ride control valve (5) Control valve (auxiliary) (6) Valve manifold (end cover) (7) Solenoid valve (lockout) (8) Ball valve (dead engine lower) (9) Accumulator (pilot supply) (10) Anti-drift valve (11) Relief valve (12) Pilot port passage (dump) (13) Pilot port passage (lower float) (14) Ride control solenoid valve (rod end) (15) Ride control solenoid valve (head end) (16) Ride control accumulator (17) Relief valve (18) Pilot passage (open raise) (19) Compensator and load check valve (20) Valve stem (auxiliary) (21) Pilot (auxiliary) (22) Spool (23) Check valve (24) Resolver (load signal) (25) Valve spool (lift) (26) Pilot passage (raise) (27) Resolver valve (load signal) (28) Valve spool (tilt) (29) Pilot port (30) Load signal relief valve (31) Pump supply (32) Drain for load signal (33) Load signal (34) Signal duplicating reducing valve (35) Supply oil from priority valve (36) Priority valve (37) Pressure reducing valve (38) Hydraulic tank port (39) Pilot supply to pilot control valve | |
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| Illustration 2 | g01432567 |
Main Control Valve with Three Functions and Ride Control (1) Valve manifold (inlet) (2) Valve manifold (tilt) (3) Valve manifold (lift) (4) Ride control valve (5) Control valve (auxiliary) (6) Valve manifold (end cover) | |
The oil flows from the implement pump through the steering priority valve (36) . The steering priority valve ensures that the steering system has all of the needed oil. When the steering system is filled with oil, the oil then flows to the main control valve.
The implement pump supplies the hydraulic oil to the main control valve. Oil flow enters the control valve and flows through a parallel feeder passage to all circuits. All circuits on the machine can be operated independently. The supply oil flows to the following components: inlet valve (1) , tilt control valve (2) , lift control valve (3) , ride control valve (4) and auxiliary valve (5) . The oil will flow into the inlet manifold (1) which diverts oil to the following components: implement lockout solenoid (7) , pilot pressure reducing valve and pilot oil accumulator (9) TILT, LIFT , ride control and DUMP. The valve operations are explained later in this document.
The oil that flows into the load sensing circuit enters the signal duplicating reducing valve (34) . Normally, the oil flows through the signal duplicating reducing valve. When no circuits are active, the centering spring keeps the spools in the control valves in the Hold position.
The control valves are proportional priority and pressure compensated. If a circuit is active, or if more than one circuit is active, the signal duplicating reducing valve (34) duplicates the highest signal oil pressure. The signal duplicating reducing valve (34) duplicates the highest signal oil pressure. The oil pressure from the signal duplicating reducing valve flows to the port for the load sensing in order to control the output of the implement pump. The load sensing implement pump will provide required flow to the system. If the pump flow is not sufficient for all of the functions, the flow of hydraulic oil to all functions is reduced proportionally.
If the signal oil pressure becomes too high, the load sensing relief valve (30) shifts. The oil then flows to the tank. When no circuits are active, signal duplicating reducing valve (34) drains the signal oil to the tank. Load signal relief valve (30) limits signal pressure to the pump. This will limit the system pressure. If the oil pressure in the load sensing circuit in the main control valve becomes too high, the relief valve (34) drains oil to the tank.
The signal duplicating reducing valve (34) and the load sensing relief valve (30) operate for all of the control valves in the main control valve. Load sensing relief valve (30) limits the maximum signal pressure to the pump at point (33) .
ReferenceFor more information on the operation or the line relief valves, refer to Systems Operation, "Relief Valve (Line)".
ReferenceFor more information on the operation of the Relief Valve (Signal), refer to Systems Operation, "Relief Valve (Signal)".
ReferenceThe operation of the ride control valve is explained in Systems Operation, "Ride Control System".
Tilt Control Valve
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| Illustration 3 | g01432245 |
Tilt Control Valve (A) Port (head end) (B) Port (rod end) (10) Anti-drift valve (11) Relief valve (12) Port passage (dump) (19) Compensator and load check valve (27) Shuttle valve (load signal) (28) Valve spool (29) Pilot port (35) Implement pump flow (38) Hydraulic tank port (40) Passage (41) Spring (42) Spring (43) Passage (44) Pilot pressure chamber (45) Passage for the anti-drift valve (46) Feeder passage (47) Spool (48) Passage (49) Spring (50) Load sensing passage (51) Passage (52) Passage (53) Chamber | |
HOLD Position
In the HOLD position, spring (41) and spring (42) hold spool (28) in position. The oil in passage (35) is blocked by spool (28) . No pilot oil enters the valve in port (29) or port (12) . Any oil in the pilot lines drains through the pilot valve to the tank.
Passage (35) is common to all valves in the main control valve. The passage has no outlet. Oil does not enter the valve until the operator moves the pilot valve.
DUMP Position
When the operator moves the pilot valve to the DUMP position, pilot oil flows from pilot line into port (29) . The pilot oil flows through passage (43) into chamber (44) and into passage (45) . When the oil pressure overcomes the force of spring (42) , the spool (28) moves to the right. Pump supply oil flows from passage (35) . The oil flows around the spool into feeder passage (46) .
As the oil flows into the feeder passage, oil pressure increases. This increase in oil pressure causes the spool (47) to move upward. The oil flows through the spool (47) to the spool (28) . On the left side of the passage (40) , the spool blocks the flow of oil. On the right side of the passage (40) , the oil flows through the spool to passage (48) . The oil flows through port (B) . The oil flows to the rod end of the tilt cylinders on the 938H. The oil flows to the head end of the tilt cylinders on the IT38H.
Some of the oil that flows through the spool (47) flows around the spool into the spring chamber that is on top of the spool. The flow of oil into the spring chamber causes the oil pressure in the chamber to increase. The force of the spring (49) and the oil pressure in the spring chamber will equal the oil pressure that is flowing to the tilt cylinders.
The oil flows through the resolver and into the spring chamber. If this circuit is the only circuit that is active, or this circuit has a work port pressure that is higher than the other circuits that are active, the load sensing pressure flows into the load sensing passage (50) until the oil pressure in the load sensing passage is equal to the oil pressure that flows to the work tool. This pressure flows to the pump actuator group in order to control the output from the pump.
Pilot oil in passage (45) flows to the pilot operated anti-drift valve (10) . When the oil pressure overcomes the force of the spring that is in the pilot operated check valve, the pilot operated check valve opens. Oil from the head end of the tilt cylinder flows through port (A) to passage (51) . The oil flows through the pilot operated check valve to the passage (52) .
The oil flow is different in the IT38H only. In the IT38H, the tilt control valve contains a regeneration circuit in the DUMP circuit. Oil flows from port (A) to passage (52) . The spool blocks the flow of the oil to passage (38) . The oil flows along the spool. The oil combines with pump flow from passage (46) . The combined flow enters passage (48) . The oil then flows through port (B) to the head end of the cylinders.
When the operator releases the pilot valve, the pilot oil flows toward the pilot valve and to the tank. Spring (41) moves spool (28) to the HOLD position. Then pilot operated anti-drift valve (10) closes. The oil in passage (40) drains through the hole and the passage inside spool (28) to passage (38) . The oil then drains to the tank. Pilot operated check valve (23) blocks the hydraulic oil in the hydraulic lines to the rod end of the tilt cylinder.
TILTBACK Position
When the operator moves the pilot valve to the TILTBACK position, pilot oil flows from pilot line into passage (12) . The pilot oil flows through passage (12) into chamber (53) . When the oil pressure overcomes the force of spring (41) , the spool (28) moves to the left. Pump supply oil flows from passage (35) around the spool into feeder passage (46) .
As the oil flows into the feeder passage, oil pressure increases. This increase in oil pressure causes the spool (47) to move upward. The oil flows through the spool (47) to the spool (28) . On the right side, oil flows from port (B) to passage (48) . The oil then flows across spool (28) and into passage (38) . The oil then flows to the tank. On the left side, the oil flows through the spool to passage (52) . As the oil flows into passage (52) , the oil pressure increases. When the oil pressure overcomes the force of the spring inside the pilot operated anti-drift valve (10) , the pilot operated check valve opens. The oil flows through the check valve into passage (51) . Then, the oil flows through port (A) to the head end of the tilt cylinders for the 938H only.
Some of the oil that flows through the spool (47) flows around the spool into the spring chamber that is on top of the spool. The flow of oil into the spring chamber causes the oil pressure in the chamber to increase. The force of the spring (49) and the oil pressure in the spring chamber will equal the oil pressure that is flowing to the tilt cylinders.
The oil flows through the resolver and into the spring chamber. If this circuit is the only circuit that is active, or this circuit has a work port pressure that is higher than the other circuits that are active, the load sensing pressure flows into the load sensing passage (50) until the oil pressure in the load sensing passage is equal to the oil pressure that flows to the work tool. This pressure flows to the pump actuator group in order to control the output from the pump.
Oil from the head end of the tilt cylinder flows through port (B) and passage (48) . The oil flows around spool (28) to passage (38) . Then, the oil flows to the tank.
When the operator releases the pilot valve, the pilot oil flows toward the pilot valve and to the tank. Spring (41) moves spool (28) to the HOLD position. The oil in passage (40) drains through the hole and the passage inside spool (28) to passage (38) . The oil then drains to the tank. Pilot operated anti-drift valve (10) blocks the hydraulic oil in the hydraulic lines to the rod end of the tilt cylinder.
ReferenceFor more information on the operation or the line relief valves, refer to Systems Operation, "Relief Valve (Line)".
Lift Control Valve
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| Illustration 4 | g01432266 |
Lift Control Valve (A) Port (head end) (B) Port (rod end) (10) Check valve (13) Pilot port (raise) (19) Compensator and load check valve (24) Shuttle valve (load signal) (25) Valve spool (26) Pilot port (float position or lower position) (35) Pump port (38) Hydraulic tank port (40) Passage (41) Spring (42) Spring (44) Chamber (46) Feeder passage (47) Spool (49) Spring (50) Load sensing passage (51) Passage (52) Passage (53) Chamber (54) Passage | |
HOLD Position
In the HOLD position, spring (41) and spring (42) hold spool (25) in position. The oil in passage (35) is blocked by spool (25) . No pilot oil enters the valve in port (26) or port (13) . Any oil in the pilot lines drains through the pilot valve to the tank.
Passage (35) is common to all valves in the main control valve. The passage has no outlet. Oil does not enter the valve until the operator moves the pilot valve.
RAISE Position
When the operator moves the pilot valve to the RAISE position, pilot oil flows from pilot line into port (13) . The pilot oil flows through passage (54) into chamber (53) . When the oil pressure overcomes the force of spring (41) , the spool (25) moves to the left. Pump supply oil flows from passage (35) around the spool into feeder passage (46) .
As the oil flows into the feeder passage, oil pressure increases. This increase in oil pressure causes the spool (47) to move upward. The oil flows through the spool (47) to the spool (25) . On the right side, oil flows from port (B) to passage (48) . The oil then flows across spool (28) and into passage (38) . The oil then flows to the tank. On the left side of the feeder passage, the oil flows through the spool to passage (52) . As the oil flows into passage (52) , the oil pressure increases. When the oil pressure overcomes the force of the spring inside the pilot operated check valve (10) , the pilot operated check valve opens. The oil flows through the check valve into passage (51) . Then, the oil flows through port (A) to the head end of the lift cylinders.
Some of the oil that flows through the spool (47) flows around the spool into the spring chamber that is on top of the spool. The flow of oil into the spring chamber causes the oil pressure in the chamber to increase. The force of the spring (19) and the oil pressure in the spring chamber will equal the oil pressure that is flowing to the tilt cylinders.
The oil flows through the resolver and into the spring chamber. If this circuit is the only circuit that is active, or this circuit has a work port pressure that is higher than the other circuits that are active, the load sensing pressure flows into the load sensing passage (50) until the oil pressure in the load sensing passage is equal to the oil pressure that flows to the work tool. This pressure flows to the pump actuator group in order to control the output from the pump.
Oil from the rod end of the lift cylinder flows through port (B) and passage (48) . The oil flows around spool (25) to passage (38) . Then, the oil flows to the tank.
When the operator releases the pilot valve, the pilot oil flows toward the pilot valve and to the tank. Pilot operated anti-drift valve (10) closes. Spring (42) moves spool (25) to the HOLD position. The oil in passage (40) drains through the hole and the passage inside spool (25) to passage (38) . The oil then drains to the tank. Pilot operated check valve (10) blocks the hydraulic oil in the hydraulic lines to the head end of the lift cylinder.
LOWER Position
When the operator moves the pilot valve to the LOWER position, pilot oil flows from pilot line into port (26) . The pilot oil flows through passage (43) into chamber (44) and into passage (45) . When the oil pressure overcomes the force of spring (41) , the spool (25) moves to the right. Pump supply oil flows from passage (25) . The oil flows around the spool into feeder passage (46) .
As the oil flows into the feeder passage, oil pressure increases. This increase in oil pressure causes the spool (47) to move upward. The oil flows through the spool (47) to the spool (25) . On the right side, oil flows from port (B) to passage (48) . The oil then flows across spool (28) and into passage (38) . The oil then flows to the tank. On the right side of the passage (40) , the oil flows through the spool to passage (48) . The oil flows through port (B) to the rod end of the lift cylinders.
Some of the oil that flows through the spool (47) flows around the spool into the spring chamber that is on top of the spool. The flow of oil into the spring chamber causes the oil pressure in the chamber to increase. The force of the spring (49) and the oil pressure in the spring chamber will equal the oil pressure that is flowing to the tilt cylinders.
The oil flows through the resolver and into the spring chamber. If this circuit is the only circuit that is active, or this circuit has a work port pressure that is higher than the other circuits that are active, the load sensing pressure flows into the load sensing passage (50) until the oil pressure in the load sensing passage is equal to the oil pressure that flows to the work tool. This pressure flows to the pump actuator group in order to control the output from the pump.
Pilot oil in passage (45) flows to the pilot operated anti-drift valve (10) . When the oil pressure overcomes the force of the spring that is in the pilot operated check valve, the pilot operated check valve opens. Oil from the head end of the lift cylinder flows through port (A) to passage (51) . The oil flows through the pilot operated check valve to passage (52) . The oil flows around the spool (25) to passage (38) . Then, the oil flows to the tank.
When the operator releases the pilot valve, the pilot oil flows toward the pilot valve and to the tank. Pilot operated anti-drift valve (10) closes. Spring (42) moves spool (25) to the HOLD position. The oil in passage (40) drains through the hole and the passage inside spool (25) to passage (38) . The oil then drains to the tank. Pilot operated check valve (10) blocks the hydraulic oil in the hydraulic lines to the rod end of the tilt cylinder.
FLOAT Operation
When the operator moves the pilot valve to the FLOAT position, pilot oil flows from pilot line into port (26) . The pilot oil flows through passage (43) into chamber (44) and into passage (45) . When the oil pressure overcomes the force of spring (42) , the spool (25) moves completely to the right. The spool (25) blocks the flow of pump oil from passage (35) . When the spool (25) moves completely to the right, the passage (52) and the passage (48) connect to passage (38) .
Pilot oil in passage (45) flows to the pilot operated check valve (10) . When the oil pressure overcomes the force of the spring that is in the pilot operated check valve, the pilot operated check valve opens. Oil from the head end of the lift cylinder flows through port (1) to passage (51) . The oil flows through port (A) to passage (52) . The oil flows around the spool (25) to passage (38) . Then, the oil flows to the tank.
Oil from the rod end of the lift cylinder flows through port (B) to the passage (48) . The oil flows around the spool (25) to passage (38) . Then, the oil flows to the tank.
When the operator moves the pilot valve to the FLOAT position, port (A) and port (B) connect to the tank. The oil from the rod end of the lift cylinder and the oil from the head end of the lift cylinder drains to the tank. This allows the weight of the lift arm assembly to lower the lift arm assembly to the ground. The lift arm assembly will follow the contour of the ground. Neither the rod end of the lift cylinder or the head end of the lift cylinder are under hydraulic pressure.
Ride Control Valve
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| Illustration 5 | g01434800 |
Ride control valve (4) Ride control valve (10) Check valve (14) Ride control solenoid valve (15) Ride control solenoid valve (16) Ride control accumulator (22) Spool (23) Check valve (C) Port (rod end) (D) Tank port (E) Port (head end) | |
Ride control valve (4) is an optional control valve. This function provides dampening for the forces that are produced by the bucket as the machine travels over rough terrain. Ride control valve (4) has three positions: AUTO, OFF and SERVICE.
Ride control valve (4) contains solenoid valve (14) which is an On, Off valve. The pump charges accumulator (16) , spool (22) , and check valve (23) . The pressure in accumulator (16) is balanced by spool (22) . The pressure is equal between the accumulator (16) and the lift cylinder. Spool (22) drains accumulator 16 in order to match the pressures.
Check valve (10) and ride control solenoid valve (14) pass oil when ride control accumulator (16) is on. Check valve (10) and ride control solenoid valve (14) do not charge ride control accumulator (16) .
Ride control valve (4) also contains solenoid valves (14) and (15) . When the ride control system is activated, solenoid valve (14) allows oil to enter the ride control valve from the rod end of the lift cylinder at port (C) . Oil exits the ride control valve at tank port (D) . Solenoid valve (15) works with check valve (10) in order to allow oil from the head end of the lift cylinder to mix with oil from ride control accumulator (15) at port (E) . Nitrogen gas in ride control accumulator (15) acts as a shock absorber for the lift circuit.
ReferenceThe operation of ride control valve (4) is explained in Systems Operation, "Ride Control System".
Auxiliary Control Valve
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| Illustration 6 | g01518685 |
Auxiliary Control Valve (A) Work port to head end of auxiliary cylinder (B) Work port to rod end of auxiliary cylinder (5) Control valve (auxiliary) (10) Check valve (17) Relief valve (18) Pilot (open raise) (19) Compensator and load check valve (20) Valve stem (auxiliary) (21) Pilot (close lower) (35) Pump port (38) Tank port (40) Bridge passage (41) Spring (42) Spring (46) Feeder passage (47) Spool (48) Passage (50) Passage (52) Passage (53) Chamber (54) Passage | |
HOLD Position
In the HOLD position, spring (41) and spring (42) hold spool (25) in position. The oil in passage (35) is blocked by spool (25) . No pilot oil enters the valve in port (21) or port (18) . Any oil in the pilot lines drains through the pilot valve to the tank.
Passage (35) is common to all valves in the main control valve. The passage has no outlet. Oil does not enter the valve until the operator moves the pilot valve.
When the oil exits the control valve through port (A) , pilot oil flows from pilot line into port (21) . The pilot oil flows through passage (43) into chamber (44) . When the oil pressure overcomes the force of spring (42) , the spool (20) moves to the right. Pump supply oil flows from passage (25) around the spool into feeder passage (46) .
As the oil flows into the feeder passage, oil pressure increases. This increase in oil pressure causes the spool (47) to move upward. The oil flows through the spool (47) to the spool (20) . On the right side of the feeder passage, the spool blocks the flow of oil. On the left side of the feeder passage, the oil flows through the spool to passage (52) . Then, the oil flows through port (A) to the auxiliary circuit.
Some of the oil that flows through the spool (20) flows around the spool into the spring chamber that is on top of the spool. The flow of oil into the spring chamber causes the oil pressure in the chamber to increase. The force of the spring (19) and the oil pressure in the spring chamber will equal the oil pressure that is flowing to the tilt cylinders.
The oil flows through the resolver and into the spring chamber. If this circuit is the only circuit that is active, or this circuit has a work port pressure that is higher than the other circuits that are active, the load sensing pressure flows into the load sensing passage (50) until the oil pressure in the load sensing passage is equal to the oil pressure that flows to the work tool. This pressure flows to the pump actuator group in order to control the output from the pump.
Oil flows to the auxiliary circuit through port (B) and passage (48) . The oil flows around spool (20) to passage (38) . Then, the oil flows to the tank.
When the operator releases the pilot valve, the pilot oil flows toward the pilot valve and to the tank. The pilot operated check valve closes. Spring (42) moves spool (20) to the HOLD position. The oil in passage (40) drains through the hole and the passage inside spool (20) to passage (38) . The oil then drains to the tank. The pilot operated check valve blocks the hydraulic oil in the hydraulic lines to the head end of the lift cylinder.
When the oil exits the control valve port (B) , pilot oil flows from pilot line into port (18) . The pilot oil flows through passage (54) into chamber (53) . When the oil pressure overcomes the force of spring (41) , the spool (20) moves to the left. Pump supply oil flows from passage (35) . The oil flows around the spool into feeder passage (46) .
As the oil flows into the feeder passage, oil pressure increases. This increase in oil pressure causes the spool (47) to move upward. The oil flows through the spool (47) to the spool (20) . On the left side of the passage (40) , the spool blocks the flow of oil. On the right side of the passage (40) , the oil flows through the spool to passage (48) . The oil flows through port (B) to the auxiliary circuit.
Some of the oil that flows through the spool (47) flows around the spool into the spring chamber that is on top of the spool. The flow of oil into the spring chamber causes the oil pressure in the chamber to increase. The force of the spring (47) and the oil pressure in the spring chamber will equal the oil pressure that is flowing to the tilt cylinders.
The oil pressure in the spring chamber is sensed in the resolver. If this circuit is the only circuit that is active, or this circuit has a work port pressure that is higher than the other circuits that are active, the load sensing pressure flows into the load sensing passage (50) until the oil pressure in the load sensing passage is equal to the oil pressure that flows to the work tool. This pressure flows to the pump actuator group in order to control the output from the pump.
Oil from the auxiliary circuit flows through port (A) to passage (52) . The oil flows around the spool (20) to passage (38) . Then, the oil flows to the tank.
When the operator releases the pilot valve, the pilot oil flows toward the pilot valve and to the tank. Pilot operated anti-drift valve (10) closes. Spring (42) moves spool (25) to the HOLD position. The oil in passage (40) drains through the hole and the passage inside spool (20) to passage (38) . The oil then drains to the tank. The pilot operated check valve blocks the hydraulic oil in the hydraulic lines to the rod end of the tilt cylinder.
Ball Valve Gp (Dead Engine Lower)
The ball valve (8) for lowering the loader arms is connected to the head end of the lift cylinders. The ball valve for lowering the loader arms is located on the front frame next to the top articulation joint. You use the ball valve when the engine will not start and the lift arms are raised. When you turn the stem of the ball valve, the lift arms will lower to the ground. Oil from the head end of the lift cylinders will flow through the ball valve to the tank. Refer to Operation and Maintenance Manual, "Equipment Lowering with Engine Stopped" for additional information on the operation of the ball valve.