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| Illustration 1 | g00822780 |
(1) Pilot operated hydraulic control ( hydrostatic) (2) Pilot operated hydraulic control ( work tool) (3) Bank valve (4) Interlock manifold valve (5) Accumulator (6) Return manifold (7) Speed sensing valve (8) Charge relief valve (9) Piston pump ( hydrostatic) (10) Gear pump | |
The pilot hydraulic system is used to move the spools in the bank valve and the pilot hydraulic system is used to control the operation of the hydrostatic system. The pilot hydraulic system uses lower pressure oil to control higher pressure oil. The pilot hydraulic system consists of the following components: (1) pilot operated hydraulic control ( hydrostatic), (2) pilot operated hydraulic control ( work tool), (3) bank valve, (4) interlock manifold valve, (5) accumulator, (6) return manifold, (7) speed sensing valve, (8) charge relief valve, (9) piston pump ( hydrostatic) and (10) gear pump.
The oil for the pilot hydraulic system is supplied by the gear pump (10). The speed sensing valve (7) in the piston pump ( hydrostatic) (9) regulates the pilot system oil. The gear pump turns at engine speed. The pilot system pressure increases when the speed of the engine increases.
In order for pilot oil to flow to the pilot operated hydraulic controls, the interlocks must be disengaged. In order for the interlocks to be disengaged, the following conditions must be met:
- The seat must be occupied.
- The armrest must be in the DOWN position.
- The parking brake must be disengaged.
When the interlock system is disengaged, oil flows from the front section of the gear pump through the gear motor ( fan drive) and the oil filter to the piston pump ( hydrostatic). The speed sensing valve allows some oil to flow to the pilot operated hydraulic control ( hydrostatic). The pressure of this oil is 2200 kPa (320 psi) at high idle.
The charge relief valve (8) regulates the pressure of the remaining oil. The charge system pressure is 3300 kPa (480 psi) at high idle. Some of the remaining oil will flow to the pilot operated hydraulic control ( work tool) and the rest of the oil is charge oil for the hydrostatic system.
Pilot Operated Hydraulic Control ( Hydrostatic)
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| Illustration 2 | g00822817 |
(1) Pilot operated hydraulic control ( hydrostatic) (4) Interlock manifold valve (7) Speed sensing valve (9) Piston pump ( hydrostatic) (11) Resolver network (12) Solenoid valve ( hydrostatic) (13) Solenoid valve ( parking brake) (14) Solenoid valve ( work tool) (15) Left piston motor ( hydrostatic) (16) Right piston motor ( hydrostatic) (17) Actuator piston (18) Actuator piston (A) Hystat pressure port (B) Hystat pressure port (X3) Pilot pressure port (X4) Pilot pressure port | |
Oil that comes from the speed sensing valve (7) flows to the pilot operated hydraulic control ( hydrostatic) (1). When the interlock system (4) is disengaged, signal oil will not flow through the pilot operated hydraulic control until the hydraulic control is moved out of the HOLD position. The hydraulic control will return to the HOLD position when the hydraulic control is released from any of the positions. Table 1 shows the direction of machine travel when the signal ports are pressurized by the pilot operated hydraulic control ( hydrostatic).
| Ports that are Pressurized | Direction of Machine Travel |
| Port (X3) on Pump 1 and Port (X3) on Pump 2 | REVERSE |
| Port (X3) on Pump 1 and Port (X4) on Pump 2 | LEFT TURN |
| Port (X4) on Pump 1 and Port (X3) on Pump 2 | RIGHT TURN |
| Port (X4) on Pump 1 and Port (X4) on Pump 2 | FORWARD |
When the hydraulic control is moved to the FORWARD position, signal oil flows from the speed sensing valve (7) through the solenoid valve ( hydrostatic) (12) in the interlock manifold (4). Then, the oil flows through the plunger in the hydraulic control that is for the FORWARD position. Oil then flows into the resolver network (11). When the balls in the resolver network are unseated, the resolver network routes the signal oil to the two pumps (9). In the following example, the signal oil is routed to the ports (X4) that are on the piston pump. The signal oil flows into the ports (X4) and the signal oil shifts the actuator pistons (17) and (18). This causes the swashplates to move and oil flows out of the ports (A) on the piston pumps. This will propel the machine forward.
When the operator releases the hydraulic control, the hydraulic control returns to the HOLD position. This causes the flow of pilot oil to stop. The actuator pistons will return to the center position and the swashplates will move back to the minimum displacement position. No oil will flow out of the piston pump. This causes the machine to stop.
Refer to the Systems Operation, "Piston Pump (Hydrostatic)" for more information on the piston pump. Refer to the Systems Operation, "Piston Motor (Hydrostatic)" for more information on the piston motor.
Pilot Operated Hydraulic Control ( Work Tool)
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| Illustration 3 | g00822815 |
(2) Pilot operated hydraulic control ( work tool) (3) Bank valve (4) Interlock manifold valve (5) Accumulator (9) Piston pump ( hydrostatic) (13) Solenoid valve ( parking brake) (14) Solenoid valve ( work tool) (19) Lift cylinders (20) Tilt cylinders (21) Auxiliary couplings (22) Modulating valve (23) Modulating valve | |
Oil flows from the charge pressure system in the piston pump ( hydrostatic) (9). The oil flows into the interlock manifold valve (4) and to the solenoid valve ( work tool) (14) and the solenoid valve ( parking brake) (13). The pilot oil flows from the solenoid valve ( work tool) to the pilot operated hydraulic control ( work tool) (2). The pilot operated hydraulic control controls the lift cylinders (19) and the tilt cylinders (20) through the bank valve (3). The hydraulic control also controls the auxiliary couplings (21) through the modulating valves (22) and (23) in the interlock manifold valve.
The interlock system must be disengaged for the pilot oil to flow. The auxiliary circuit can function with the armrest in the UP position, if the machine is equipped with an interlock override control. Refer to the Operation and Maintenance Manual, SEBU7468, "Continuous Flow and Interlock Override Control" for more information.
When the interlock system (4) is disengaged, pilot oil will not flow through the hydraulic control until the hydraulic control is moved out of the HOLD position. The hydraulic control will return to the HOLD position when the hydraulic control is released from any of the positions except for the FLOAT position. The FLOAT position has a detent that keeps the hydraulic control in this position until the operator moves the hydraulic control.
When the hydraulic control is moved to the TILT BACK position, pilot oil flows through the solenoid valve (work tool) (14). Then, the pilot oil flows through the plunger in the hydraulic control that is for the TILT BACK position. Then, the pilot oil flows to the bank valve in order to shift the tilt control valve to the TILT BACK position. Oil then flows out of port (A) to the rod ends of the tilt cylinders (20) in order to tilt the work tool backward. When the operator releases the hydraulic control, the hydraulic control will move back to the HOLD position. This shuts off the flow of pilot oil. The tilt control valve will move back to the HOLD position and the tilt cylinders will stop retracting.
Refer to the Systems Operation, "Bank Valve" for more information on the control valve.
Accumulator
The oil flows from the piston pump ( hydrostatic) to the interlock manifold valve. The accumulator (5) is mounted on the front of the interlock manifold valve. The accumulator provides a limited amount of pilot oil after the engine is shut off. The oil capacity of the accumulator is 0.5 L (0.53 qt). The accumulator is charged to 900 kPa (130 psi) with 30.0 cc (1.83 in3) of dry nitrogen.