SHIELD 7N4471 - Caterpillar

When drive shaft (12) is driven, the components that rotate are cylinder barrel (9), piston assemblies (10), and plate (2). There are nine piston assemblies in cylinder barrel (9).Oil from the hydraulic tank flows into pump head (7) through pump inlet (8). The oil then flows from pump inlet (8) through inlet passages in valve plate (4). When drive shaft (12) rotates, the openings of cylinder barrel (9) move toward the inlet passages of valve plate (4).Each piston assembly (10) inside cylinder barrel (9) is held against swashplate (11) by plate (2). Swashplate (11) can be at any angle between the maximum angle and the neutral angle.The angle of swashplate (11) determines the amount of oil that is pushed out of each cylinder barrel (9). Swashplate (11) can be at any angle between the neutral angle and the maximum angle. The neutral angle is perpendicular with drive shaft (12). When swashplate (11) is at the neutral angle, piston assemblies (10) do not move in and out of rotating cylinder barrel (9). Therefore, no oil is drawn into the pump and no oil is pushed out of the pump. The pump has zero displacement and a small amount of flow for leakage.When swashplate (11) is at the maximum angle, piston assemblies (10) move in and out of cylinder barrel (9). The movement of the piston assemblies (10) allows the maximum amount of oil to be drawn into the cylinder barrel (9). The pump will produce the maximum flow.The swashplate angle is controlled by actuator piston (3). The movement of the actuator piston (3) is regulated by oil pressure from pressure compensator valve (6).
Illustration 2 g06060636
Pressure compensator valve
(6) Pressure compensator valve
(13) Pressure compensator spring
(14) Case drain passage
(15) Orifice valve
(16) Signal passage to the actuator piston
(17) Pressure compensator spool
(18) Pump pressure passage
(19) High-pressure cutoff valvePressure compensator valve (6) is mounted to the pump. Pressure compensator valve (6) contains one spool. Pressure compensator spool (17) regulates the pump pressure output in response to pump pressure passage (18).Pressure compensator valve (6) maintains the correct oil pressure. The pressure of the pump is maintained by sending pump oil to control piston (3) or draining pump oil from control piston (3).Control piston (3) and bias spring (1) work together to adjust the angle of swashplate (11). Pressure compensator valve (6) adjusts pump flow to the load.Note: The High Pressure Cut off valve prevents overloading of the pump, not the pressure compensator valve.Pump Destroke
Illustration 3 g06060346
Piston pump in destroke
(1) Bias spring
(3) Actuator piston
(5) Pump outlet port
(11) Swashplate
(13) Pressure Compensator spring
(14) Case drain passage
(15) Orifice valve
(16) Signal pressure to the actuator piston
(17) Pressure compensator spoolThe hydraulic system pressure is sensed by the pressure compensator spool through passage (5). As pressure increases in passage (5), Pressure Compensator spool (17) acts on pressure compensator spring (13) and increases signal pressure to actuator piston (3).When the oil pressure behind actuator piston (3) is sufficient, the piston will start to move. The piston rod will push swashplate (11) against bias spring (1). Swashplate