GASKET 7N6670 - Caterpillar

Illustration 3 g00270338
Metering Position
(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 flow compensator spool (12).The force of spring (14) causes pump pressure to be greater than signal pressure by the amount of the margin pressure setting.Reference: See the specifications manual for the machine that is being serviced for the margin pressure setting.With the spool in position A, pump pressure is greater than the combined force of spring (14) and of the signal oil pressure in cavity (18). This forces flow compensator spool (12) to move upward.When flow compensator spool (12) moves upward, pressure oil flows past the spool. The oil then flows through passage (19). The oil flows past pressure compensator spool (13) and into passage (20). Oil flows through passage (20) to actuator piston (10).The area of actuator piston (10) is larger than the area of bias piston (4). The force of the oil that is acting against actuator piston (10) overcomes the combined force of spring (6) and of the oil that is acting against bias piston (4). Actuator piston (10) moves to the right. This causes swashplate (2) to move toward the minimum angle. As the angle of swashplate (2) decreases, pump output also decreases. When the pump pressure is low enough, the combined force of the signal oil pressure in cavity (18) and of spring (14) causes flow compensator spool (12) to move downward into position B.When flow compensator spool (12) moves down, the flow of pump output oil into passage (19) is blocked. Oil in passage (20) flows from actuator piston (10) past pressure compensator spool (13). The oil then returns to the case drain.Destroking
Illustration 4 g00270340
Pump and compensator operation
(2) Swashplate. (4) Bias piston. (6) Bias spring. (10) Actuator piston. (12) Flow compensator spool. (13) Pressure compensator spool. (14) Spring. (15) Spring. (16) Line to priority valve for brake. (17) Signal line from resolvers. (18) Cavity. (19) Passage. (20) Passage. (21) Passage. (22) Passage. (23) Passage. (24) Case drain. (A) Signal pressure oil. (B) System pressure oil. (C) Return oil.
Destroking of the pump occurs because of decreased flow demand. The decreased flow demand is met by decreased pump output. The decreased flow demand causes a signal pressure in line (17) that combines with the force of spring (14) in cavity (18). This combination of signal pressure and of spring force is less than the pump pressure in passage (21). This causes flow compensator spool (12) to move upward. The oil behind actuator piston (10) cannot flow through passage (22) to case drain (24). Pump oil now flows through passage (21). The oil then flows past flow compensator spool (12), through passage (20) and into 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 the swashplate (2) decreases. This decreases the pump output