Piston Pump
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| Illustration 1 | g00932836 |
Location of the Piston Pump | |
The piston pump is attached to the front of the engine. Open the access door on the right side of the machine in order to view the piston pump.
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| Illustration 2 | g00850226 |
Piston Pump (1) Swashplate (2) Displacement control valve (3) Servo arm (4) Servo piston (5) Servo cylinder (6) Port (7) Port (8) Barrel (9) Piston (10) Shoe plate (11) Input shaft | |
The piston pump is an axial piston pump that can vary the pump displacement. The piston pump is attached to the engine. The pump displacement and the direction of oil flow from the pump is controlled by the positioning of swashplate (1). Displacement control valve (2) controls the maximum amount of displacement and the direction of oil flow from the pump. The maximum displacement of the pump can be lowered in order to limit the machine speed.
The piston pump is driven by the engine through input shaft (11). The piston pump will rotate in the same direction as the engine turns. Input shaft (11) drives barrel (8). Barrel (8) carries nine pistons (9). Pistons (9) move hydraulic oil into the cylinders that are inside barrel (8). Likewise, pistons (9) move hydraulic oil out of the cylinders that are inside barrel (8). The nine pistons (9) are mounted in shoe plates (10) .
Displacement Control Valve
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| Illustration 3 | g00854263 |
(1) Swashplate (2) Servo arm (3) Servo piston (4) Displacement control valve (5) Charge pump (6) Multifunction valve (7) Pressure relief valve (8) Port (9) Servo cylinder (10) Barrel (11) Shoe plate (12) Piston (13) Port | |
Displacement control valve (4) directs oil from charge pump (5) to servo control cylinder (9). Oil fills one side of servo control cylinder (9). This will move servo piston (3) inside servo cylinder (9). Servo piston (3) is connected to swashplate (1) by servo arm (2). Movement of servo piston (3) will tilt swashplate (1). The angle of tilt of swashplate (1) controls the amount and the direction of oil flow from the pump. Piston (12) is mounted by a ball in a socket on shoe plate (11). Shoe plate (11) is mounted on a bearing. This allows shoe plate (11) to rotate on swashplate (1). Swashplate (1) is tilted. When shoe plate (11) rotates past the side of the swashplate that is farthest from barrel (10), piston (12) moves out of barrel (10). This draws oil into the cylinder of barrel (10). When shoe plate (11) rotates past the side of the swashplate that is closest to barrel (10), piston (12) moves into barrel (12). This pushes oil out of the cylinder of barrel (10). Oil that flows into barrel (10) or oil that flows out of barrel (10) flows through ports (8) and (13) .
Multifunction Valve
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| Illustration 4 | g00853805 |
Multifunction Valve (1) Check valve poppet (2) High pressure relief valve poppet (3) Pressure limiter valve poppet (4) Bypass actuator nut | |
Each multifunction valve incorporates the four following individual valves:
- A check valve
- A pressure limiter valve
- A high pressure relief valve
- A bypass valve for towing the machine
Check Valve
Check valve (1) for the system is a poppet valve. The check valve is located within the multifunction valve. The check valve allows pressurized oil flow from the charge pump into the low pressure side of the drive loop whenever the system pressure drops. This replaces oil that is lost due to internal leakage through system components.
Pressure Limiter and High Pressure Relief Valves
Pressure limiter valve (3) and high pressure relief valve (2) for the system are both poppet type valves. Both valves are located within the multifunction valve. The pressure limiter valve sends pressurized oil in order to destroke the pump. Destroking the pump will limit the system pressure. The high pressure relief valve operates at a higher pressure setting than the pressure limiter. The high pressure relief valve will reduce the system pressure by relieving the system pressure to the low pressure side of the drive loop. The pressure limiter valve supplies pilot oil in order to aid the operation of the high pressure relief valve.
Bypass Valve
The bypass valve for towing is located within the multifunction valve. Turn bypass actuator nut (4) in a counterclockwise direction in order to actuate the bypass valve. Refer to Operation and Maintenance Manual, "Towing the Machine" for more information. The machine must only be towed short distances at a slow speed. When the bypass valve is in operation the setting for the pressure limiter valve is reduced to near zero. This allows any pressurized oil from the motor to flow through the case for the hydrostatic piston pump to the hydraulic tank.