The implement pump is a variable displacement axial piston pump. The pump allows variable pressure control with load sensing control.
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| Illustration 1 | g00566198 |
View Under the Cab (1) Implement pump. (2) Power train pump. (A) Pressure line. (B) Case drain line. (C) Inlet line from tank. | |
Oil enters the implement pump from the hydraulic oil tank through inlet line (C). Case drain oil exits the pump through port (B). The case drain oil cools the pump. Also, the case drain oil removes debris from the pump. The case drain oil is filtered by a case drain filter before flowing back to the hydraulic oil tank.
Pressure oil flows from the pump through line (A). The oil flows to the implement control valve, the combination valve, the steering metering pump, the bogie control valve, and the brake charging valve.
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| Illustration 2 | g00811172 |
Bottom View of the Implement Pump (3) Load sensing valve (standby and margin pressure). (4) Pressure cutoff valve. (D) Load sensing line. | |
The required output from the implement pump is sensed in load sensing line (D). Load sensing valve (3) controls the upstroking and destroking of the pump in order to match the required flow and required pressure of the system.
The load sensing valve compares the output pressure from line (A) to the signal pressure in line (D). The difference between the two pressures is the margin pressure. The load sensing valve can be adjusted in order to control the response of the pump to the pressure and flow requirements of the system.
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| Illustration 3 | g00566131 |
Schematic of the Implement Pump (3) Load sensing valve. (4) Pressure cutoff valve. (5) Swashplate. (6) Actuator piston. (A) Pressure line. (B) Case drain line. (C) Inlet line from tank. (D) Load sensing line. | |
When the engine is running and no functions are being used, a low pressure standby condition exists. There are no pressure or flow demands on the implement pump.
Before the engine is started, the spring in actuator piston (6) keeps the pump at maximum output. As the pump begins to turn, oil begins to flow and the pressure increases in the system because no oil flows to any hydraulic components.
As the pressure in the system increases, load sensing valve (3) moves to the right and oil flows through pressure cutoff valve (4) to the actuator piston. The actuator piston continues to destroke the pump until swashplate (5) is at the minimum angle.
When the flow requirement of the system increases, the differential pressure from port (D) to port (A) decreases. (The margin pressure decreases.) The force of the spring in load sensing valve (3) plus the oil pressure at port (D) is greater than the force of the oil pressure from port (A). The load sensing valve moves to the left. The oil from the right side of the actuator piston flows through the pressure cutoff valve to the signal limiter valve. The oil flows through the signal limiter valve to the case drain. The actuator piston moves to the right. This causes the pump to upstroke.
When the flow requirement of the system decreases, the differential pressure from port (D) to port (A) increases. (The margin pressure increases.) The force of the spring in load sensing valve (3) plus the oil pressure at port (D) is less than the force of the oil pressure from port (A). The load sensing valve moves to the right. Oil flows through the signal limiter valve and the pressure cutoff valve to the actuator piston. The actuator piston moves to the left. This causes the pump to destroke.
When a hydraulic function stalls under a load or a hydraulic function reaches the end of travel, the pressure in the system increases. A high pressure stall condition occurs. The pressure at port (D) is approximately the same pressure as the pressure at port (A). The spring in load sensing valve (3) keeps load sensing valve (3) shifted to the left.
When the output pressure exceeds the setting of pressure cutoff valve (4), the pressure cutoff valve moves to the right. Oil flows through the pressure cutoff valve to the actuator piston. The actuator piston strokes the pump to a lower output.