HANDLE 2807544 - Caterpillar

When the engine is off, spring (3) holds swashplate (6) at the maximum angle. When the engine is started, shaft (1) begins to rotate. Oil is drawn into the bore of pistons (2). Barrel (4) starts to rotate and pistons (2) stroke. This forces hydraulic oil into the hydraulic system.The pump is in low-pressure standby when the following conditions are met:
The machine is operating.
The implements are in the HOLD position.
There is no demand on the steering.As the pump produces flow, the system pressure begins to increase. The system pressure overcomes the spring force of spring (16) and the signal pressure in line (12) .Spool (20) moves up and oil flows into passage (18) to piston (9). The oil pressure inside piston (9) overcomes the spring force of spring (3) and the system pressure inside piston (22). Piston (9) moves the swashplate to the minimum angle. When the swashplate is moved to the minimum angle, the oil flows through the cross-drilled passage to the pump case. The system pressure is now at low-pressure standby.When the pump is at low-pressure standby, the pump produces enough flow in order to compensate for internal leakage. Also, the pump produces enough flow in order to maintain sufficient system pressure. Low-pressure standby is maintained in order to ensure instantaneous response under one of the following conditions:
The steering is activated.
An implement is activated.Low-pressure standby is higher than margin pressure. This characteristic is due to a higher back pressure that is created by the closed center valves that are in the HOLD position. The pump supply oil moves spool (20) upward. This compresses spring (16). Since spool (20) is moved upward, more of the pump supply oil is allowed to flow through passage (18). The oil will flow through passage (18) and flow out of the cross-drilled passage to the pump case.Upstroke
Illustration 3 g02181776
Typical example of a piston pump during upstroke (1) Pump drive shaft (2) Pistons (3) Bias spring (4) Barrel (6) Swashplate (9) Control piston (12) Signal oil (15) Spring