PLATE-WEAR 2548724 - Caterpillar

When you start the machine with the work tool controls in the HOLD position and the steering is inactive, the pump is at low pressure standby.There are no flow or pressure demands from the implements on the pump but there is signal pressure in line (19) due to the orifice in the priority spool (dynamic load sensing orifice). This maintains a charge in the signal line from the metering pump. This charge causes quick steering response.Before the engine is started, bias spring (3) holds swashplate (7) at a maximum angle. As the pump begins to turn, this causes oil to flow. The flow of oil builds up pressure in the system because of the closed centers of the implement valves.The pressure in passage (15) is felt at the bottom of the spool for flow compensator (13) and the spool for pressure compensator (12). As this pressure increases, the pressure pushes the spool for the flow compensator against spring (20). Spool (13) moves up. The movement of the spool opens passage (15) to passage (16) in order to allow the pressure oil to flow to piston (4) .The oil acts against the piston (2). The oil pressure overcomes the force of bias spring (3) and supply pressure. This causes the piston to move to the right. The piston moves the swashplate (7) toward the minimum angle. The actuator piston (4) continues to move to the right. The actuator piston (4) allows oil to drain into the case.The draining oil limits the maximum travel of the piston (2) to the right. The pump will produce enough flow in order to account for the system leakage. The pump will also produce enough flow in order to account for the leakage to the pump case.Upstroking
Illustration 4 g01298465
(1) Pump control valve (2) Piston (3) Bias spring (4) Actuator Piston (5) Slipper (6) Input shaft (7) Swashplate (8) Slipper Retainer (9) Cylinder block (10) Cylinder block spring (11) Valve plate (12) Pressure compensator spool (13) Flow compensator spool (14) Passage (15) Passage (16) Passage (17) Passage (18) Cavity (19) Signal line from the control valve (20) Spring (21) SpringWhen the pump increases the output due to the demand for the increased flow of oil, the pump is upstroking. Because of the increased flow demand, the signal pressure combines with the force of the spring (20) in the cavity (18) .This combination of signal pressure and spring force is greater than the pump discharge pressure. This combination of signal pressure and spring force causes the spool (13) to move down. As the spool moves down, the spool blocks the flow of the supply oil to piston (4). Oil in the passage (14) for piston (2) can now drain to passage (14) .The swashplate (7) upstrokes because of the force from the bias spring (3) .This increases the pump flow. As the flow requirements are satisfied the pump output pressure increases. The pressure in passage (14) moves spool (12) up to the metering position. This means