TUBE AS 1662969 - Caterpillar

When the engine is off, bias spring (15) holds swashplate (12) at the maximum angle. When the engine is started, pump drive shaft (13) begins to rotate. Oil is drawn into the bore of pistons (17). Barrel (14) starts to rotate and pistons (17) 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 (5) and signal oil (1).Spool (9) moves up and oil flows into passage (7) to control piston (11). The oil pressure inside control piston (11) overcomes the spring force of bias spring (15) and the system pressure inside bias piston (16). Control piston (11) 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 boosted by pilot pressure which is sent back into the signal network. The pump supply oil moves spool (9) upward. This compresses spring (5). Since spool (9) is moved upward, more of the pump supply oil is allowed to flow through passage (7). The oil will flow through passage (7) and flow out of the cross-drilled passage to the pump case.Upstroke
Illustration 3 g03635677
Typical example of a piston pump during upstroke
(1) Signal oil
(4) Spring (pressure compensator)
(5) Spring (flow compensator)
(7) Oil passage to the control piston
(8) Oil flow from the output port of the pump
(9) Spool (flow compensator)
(10) Spool (pressure compensator)
(11) Control piston
(12) Swashplate
(13) Pump drive shaft
(14) Barrel
(15) Bias spring
(16) Bias piston
(17) Pistons When more oil flow is needed, the hydraulic pump upstrokes. Signal oil is sent to the pressure and flow compensator valve when increased oil flow is required by the steering system. Signal oil is sent to the pressure and flow compensator valve when increased oil flow is required by the implement control valves. Both signal oil (1) and the force of spring (5) cause spool (9) to block the oil flow into passage (7). With no oil flow to control piston (11), bias spring (15) is now allowed to increase the swashplate angle. The hydraulic pump will produce more oil flow.Constant Flow
Illustration 4 g03635689
Typical example of a piston pump during constant flow
(1) Signal oil
(4) Spring (pressure compensator)
(5) Spring (flow compensator)
(7) Oil passage to the control piston
(8) Oil flow from the output port of the pump
(9) Spool (flow compensator)
(10) Spool (pressure compensator)
(11) Control piston
(12) Swashplate
(13) Pump drive shaft
(14) Barrel
(15) Bias spring
(16) Bias piston
(17) Pistons As the pump flow