HARNESS AS 8Y5571 - Caterpillar

UpstrokingUpstroking occurs when the signal pressure increases due to a high load at low pump output. The highest signal pressure goes through line (4) and the oil fills cavity (3) . The signal pressure and the force of spring (2) move spool (5) downward. This allows the oil behind actuator piston (6) to go to case drain (7) . The force of actuator spring (8) is now greater than the force behind the actuator piston. The angle of swashplate (9) increases. This increases pump output. The pump output pressure increases until the pressure in passage (12) moves spool (5) up to the metering position. Initially, pump pressure is greater than the combined force of spring (2) and the signal pressure in cavity (3) . Spool (5) moves up. Pump pressure is now sent to actuator piston (6) . This overcomes the force of actuator spring (8) .The angle of swashplate (9) decreases. Pump output decreases. When pump pressure is reduced to a certain point, the combined signal and spring force in cavity (3) moves spool (5) downward. The oil pressure behind actuator piston (6) goes back to the case drain. Spring (8) forces the angle of swashplate (9) to increase. This slight up and down spool movement is called metering. Metering keeps the pressure on both ends of spool (5) equal. The force of spring (2) is equal to 1720 kPa (249.5 psi). Therefore, pump pressure is 1720 kPa (249.5 psi) greater than signal pressure. This difference is called margin pressure.
Illustration 3 g00480488
(1) Pressure Compensator Spring (2) Flow Compensator Spring