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| Illustration 1 | g06216225 |
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View of the piston pump (implement) and the pump control valve (implement) | |
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| Illustration 2 | g03716264 |
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Piston Pump (Implement) (1) Inlet opening from the hydraulic tank (2) Control piston (3) Barrel (4) Pistons (nine) (5) Swashplate (6) Pump drive shaft (7) Spring for swashplate (8) Outlet opening to the implement hydraulic system (9) Pump control valve (implement) | |
The piston pump (implement) is a variable displacement axial piston pump. The implement pump is mounted on the right rear of the transfer case.
The implement pump has nine pistons (4). When pump drive shaft (6) turns, barrel (3), the retraction plate, and the slippers turn. The piston ends connect to the slippers. Swashplate (5) does not turn. There is a bearing journal on each side of the swashplate. The two bearing journals are inside bearings which allow movement of the swashplate. Oil flow through the passages in the pistons lubricates the internal components of the pump.
When swashplate (5) is at the maximum angle and pump drive shaft (6) is turning, pistons (4) are moved in and out of barrel (3). As the pistons move out of the barrel, the pistons create a vacuum at inlet opening from the hydraulic tank (1). The hydraulic tank pressure is maintained at a sufficient level not to allow cavitation as the oil is drawn into the pump. The oil passes through the inlet opening and into the piston bore in the barrel. As the barrel continues to turn, the pistons are pushed into the barrel as the slippers rotate up the angle of swashplate (5). The pistons push the oil from the piston bore through pump outlet opening to the implement system.
When the engine is operating, the pump will produce flow to satisfy the following conditions:
- The demand of the implement system
- The pressure setting of the pressure compensator
- The internal lubrication of the pump components
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| Illustration 3 | g03716303 |
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Pump Control Valve (implement) (9) ( 10) Pressure compensator spool (11) Springs (12) Adjustment screw for the pressure compensator (13) Flow compensator spool (14) Passage to the control piston of the piston pump (implement) (15) Passage from the outlet opening of the piston pump (implement) (16) Pump case drain passage (17) Load sensing port (18) Springs (19) Adjustment screw for the flow compensator | |
The pressure compensator regulates the output flow of the piston pump (implement). The output of the pump is controlled by the angle of the swashplate.
When the pump produces flow, the system pressure begins to increase because the oil flow is blocked at the main control valve. The increased pressure is felt at the top side of the flow compensator spool (13) and at the small end of pistons (4). Flow compensator spool (13) moves against springs (18). When no load sensing pressure exists at load sensing port (17), the spool will drain oil from the actuator piston to the case drain. This draining will occur until there is a pressure balance on flow compensator spool (13). The pump will maintain this margin pressure by increasing or decreasing the volume of the pump as needed.
When the engine is operating and the oil pressure in the implement hydraulic system is less than the pressure setting of the pressure compensator, the oil from the outlet opening of the piston pump flows through passage from the outlet opening of the piston pump (implement) (15). The oil is stopped by pressure compensator spool (10) and opposing force from springs (11). There is no flow to the control piston in the piston pump and the swashplate is at the maximum angle. When the system pressure setting has been obtained, full pump output is no longer needed. Full pump output continues, until the oil in the passage from the outlet opening of the piston pump (implement) (15) overcomes the opposing force of springs (11).
The oil in passage from the outlet opening of the piston pump (implement) (15) moves pressure compensator spool (10) to the right. The oil in the inlet passage now flows through the passage to the control piston of the piston pump (implement) (14). The flow of oil from passage to the control piston of the piston pump (implement) (14) moves the control piston. The control piston moves the swashplate toward the minimum angle. The pump output is decreased.
The stroke of pistons in the piston pump is shortened since the slippers follow the reduced swashplate angle. The shortened stroke of the pistons will continue to provide enough flow to maintain the system pressure setting. The shortened stroke of the pistons will also provide internal lubrication to the pump components.
When the pressure of the oil in the implement hydraulic system decreases, there is a decrease in the pressure of the oil in passage from the outlet opening of the piston pump (implement) (15). Springs (11) move pressure compensator spool (10) to the left. The oil flow to the control piston in passage to the control piston of the piston pump (implement) (14) decreases. The spring in the piston moves the swashplate toward the maximum angle. This movement toward the maximum angle causes the pump output to increase.