SHIM 3051770 - Caterpillar

Upstroke or Destroke and Metering
Illustration 4 g01937794
Implement pump and compensator (upstroke)
(2) Pressure cutoff valve
(10) Actuator piston
(11) Swashplate
(13) Spring
Illustration 5 g01937797
Implement pump and compensator (metering)
(2) Pressure cutoff valve
(13) Spring As soon as the implement controls are operated in order to move an implement cylinder, the cylinder load pressure or load sensing pressure is sent back to flow control valve (3). This pressure plus the force of spring (12) is generally above above the pump output standby pressure. This causes the margin pressure valve spool to move downward. This opens a passage between the margin pressure valve spool and the flow compensator valve body. This causes the pressure in actuator piston (10) to be drained through the cross passage of pressure cutoff valve (2) and the opened cross passage of margin pressure valve (1) to the pump case. The force of bias piston (5) still supplied with the pump output pressure plus spring (6) is above the force of actuator piston (10). This increases the angle of swashplate (11). The pump then UPSTROKES in order to generate more flow to the implement valve. While upstroking, the pump output pressure is equal to or below the load sensing pressure.As soon as the pump output flow is equal to the implement control flow requirement, the pump output pressure continues to raise up. When the pump output pressure equals the load sensing pressure value plus the value of spring (12), the margin pressure valve spool moves upward. This closes the opened passage of actuator piston (10) to the pump case. This also opens the passage of the pump output pressure to actuator piston (10). Once the force of actuator piston (10) balances the force of bias piston (5) plus spring (6), the swashplate is stabilized to the adequate angle position making the pump supply the required flow to the implement control. The pump output pressure is equal to the load sensing pressure plus the setting of margin pressure valve (1). The pump will maintain the flow that is required in order to maintain system pressure. The pump will stay in the METERING position until the flow requirement changes. As soon as the implement controls are operated in a way to reduce the speed of a cylinder, the required pump flow decreases. This makes the pump output pressure instantaneously increase due to the pump output flow being above the flow requirement of the implements. The pump output pressure that is flowing to margin pressure valve (1) and acting on the margin pressure valve spool end through the axial drilled orifice is above the load sensing pressure plus spring (12). This moves the spool upward. This also opens the passage that allows the pump output pressure to enter actuator piston (10). The force of bias piston (5) plus spring (6) is below the force of actuator piston (10). This decreases the angle of swashplate (11) so the pump DESTROKES and generates less flow to the implement valve.High Pressure Stall
Illustration 6 g01937803
Implement pump and compensator (high pressure stall)
(16) Load