COVER-LOCK 3380812 - Caterpillar

Illustration 2 g03363479
Pressure and Flow Compensator Valve
(11) Pump pressure passage
(12) Pump control valve
(13) Cutoff valve adjustment screw
(14) Cutoff spring
(15) Cutoff spool
(16) Margin spool adjustment
(17) Margin spring
(18) Load sensing port
(19) Margin spool
(20) Case drain passage
(21) Signal passage to the actuator pistonPump control valve (12) is mounted to the brake and the hydraulic fan pump. Pump control valve (12) contains two spools. Margin spool (19) regulates the pump output flow in response to load sensing port (18). Cutoff spool (15) protects the pump from high pressures.Pump control valve (12) maintains the correct pressure and correct oil flow. The pump is controlled by either sending pump oil to actuator piston (9) or by draining the pump oil from actuator piston (9).Actuator piston (9) and bias spring (7) work together to adjust the angle of swashplate (2). Pump control valve (12) prevents overloading of the pump.Pump Destroke
Illustration 3 g03363481
Piston Pump in Destroke
(2) Swashplate
(7) Bias spring
(9) Actuator piston
(11) Pump pressure passage
(15) Cutoff spool
(17) Margin spring
(18) Load sensing port
(19) Margin spool
(20) Case drain passage
(21) Signal passage to the actuator pistonWhen the hydraulic system requires a reduction in flow, a reduced signal is sent to load sensing port (18).High-pressure oil flows to margin spool (19) through pump pressure passage (11). When the pressure against margin spool (19) overcomes the force of both load sensing (18) and margin spring (17), margin spool (19) will begin to move.The oil will flow around the margin spool (19). Oil will flow to actuator piston (9).When the oil pressure behind actuator piston (9) is sufficient, the piston will start to move. The piston rod will push swashplate (2) against bias spring (7). Swashplate (2) will overcome bias spring (7). The swashplate (2) will move to a minimal angle. The piston pump will be destroked.Pump Upstroke
Illustration 4 g03363483
Pump Upstroke
(2) Swashplate
(7) Bias spring
(9) Actuator piston
(11) Pump pressure passage
(15) Cutoff spool
(17) Margin spring
(18) Load sensing port
(19) Margin spool
(20) Case drain passage
(21) Signal passage to actuator pistonWhen the hydraulic system requires an increase in oil flow, a signal is sent to load sensing port (18). The pressure at the load sensing port (18) is increased. The combination of the force of margin spring (17) and the margin increase of pressure at load sensing port (18) will shift margin spool (19) downward. This shifting of the spool will allow the oil that is behind actuator piston (9) to flow through signal passage (21). The oil will flow around cutoff spool (15). The oil will flow around the upper section of margin spool (19). The oil will flow through case drain passage (20) to the case drain.As the oil is metered out of the actuator piston (9), the force of bias spring (7) overcomes the pressure behind actuator piston (9). The angle of swashplate (2) begins to increase. As the angle of swashplate (2) increases, the piston pump will upstroke.Constant Flow
Illustration 5 g03363484
Pump at Constant Flow
(2) Swashplate
(7) Bias spring
(9) Actuator piston
(11) Pump pressure passage
(15) Cutoff spool
(17) Margin spring
(18) Load sensing port
(19) Margin spool
(20) Case drain passage
(21) Signal passage to actuator