ARM AS 2G8727 - Caterpillar

Illustration 3 g00270338
Metering Positions
(A) Spool position at high pump pressure. (B) Spool position at low pump pressure.
Slight upward movement and slight downward movement is called metering. Metering maintains equal pressure on each end of spool (12).With spool (12) in position A, pump pressure is greater than the combined force of spring (18) and signal oil pressure in cavity (20). This forces spool (12) to move upward.When spool (12) moves upward, pressure oil flows past the spool. The oil then flows through passage (23). The oil flows past compensator spool (12) and into passage (22). Oil flows through passage (22) to actuator piston (10). This process causes the pump to destroke.The area of actuator piston (10) is larger than the area of bias piston (4). The force of oil acting against actuator piston (10) overcomes the combined force of spring (6) and the oil acting against bias piston (4). Actuator piston (10) moves to the left. This causes swashplate (2) to move toward the minimum angle.As the angle of swashplate (2) decreases, pump output also decreases. When pump pressure is low enough, the combined force of signal oil pressure (20) and spring (18) causes spool (13) to move downward into B.When spool (13) moves down, the flow of pump output oil into passage (20) is blocked. Oil in passage (22) flows from actuator piston (10) past spool (12). The oil then returns to the case drain.Destroking
Illustration 4 g00297452
Pump and Compensator Operation
(1) Drive shaft. (2) Swashplate. (4) Bias piston. (6) Bias spring. (10) Actuator piston. (12) Flow compensator spool. (13) Pressure compensator spool. (14) Case