PLATE AS 1834008 - 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 g02902480
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 drain
(15) Passage
(16) Passage
(17) Spring
(18) Spring
(19) Signal line from the metering pump
(20) Cavity
(21) Passage
(22) Passage
(23) Cavity
(A) Signal pressure oil
(B) System pressure oil
(C) Return oil The decreased flow demand causes a signal pressure in line (19). The signal pressure in line (19) combines with the force of spring (18) in cavity (20). This combination of signal pressure and of spring force is less than the pump pressure in passage (15). This causes spool (13) to move upward.The oil behind actuator piston (10) cannot flow through passage (16) to case drain (14). Pump oil now flows through passage (15). The oil then flows past spool (13), through passage (22), and then to actuator piston (10).The pump pressure behind actuator piston (10) is now greater than the combined force of bias piston (4) and of bias spring (6). The angle of swashplate (2) decreases. This process decreases the pump output and the system pressure.When the lower flow requirements are met, flow compensator spool (12) moves downward to the metering position. Swashplate (2) maintains an angle that is sufficient to provide the lower required pressure. If the operator does not turn the steering wheel, then the pump will return to low-pressure standby.Low Pressure Standby
Illustration 5 g02902524
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 drain
(15) Passage
(16) Passage
(17) Spring
(18) Spring
(19) Signal line from the metering pump
(20) Cavity
(21) Passage
(22) Passage
(23) Cavity
(24) Cross-drilled hole
(A) Signal pressure oil
(B) System pressure oil
(C) Return oil