TUBE 3650264 - Caterpillar

Illustration 1 g01079914
(1) Pilot passage
(2) Spool
(3) Pressure compensator
(4) Spring retainer
(5) Spring
(6) Adjustment screw
(7) Stroke control actuator
(8) Bias spring
(9) Swashplate
(10) Main shaft
(11) Piston
(12) Piston assembly
(13) Vent port
(14) Valve plate
(15) Pump outlet port
(16) Stroke limiter
(17) Control passage
(18) Vent passage The auxiliary pump is a variable displacement piston pump. The auxiliary pump operates in one direction only.Main shaft (10) is engaged in the pump drive gearbox. When the engine is running, the main shaft rotates. The main shaft causes piston assembly (12) to rotate. As the piston assembly rotates, hydraulic oil is drawn from the hydraulic tank and supplied to the various implements. The auxiliary pump does not use a charge pump.The pump displacement is varied by changing the angle of swashplate (9). Stroke limiter (16) sets the maximum output flow of the pump. Bias spring (8) forces the swashplate against the stroke adjustment actuator in order to allow the pump to produce maximum output flow.Pressure compensator (3) maintains auxiliary system pressure. The pressure compensator monitors the pump displacement and the system pressure. The pressure compensator acts against bias spring (8) in order to destroke the swashplate when the pressure exceeds the set limit. When the swashplate is destroked, the pump displacement is reduced. No additional pressure relief valve is used.Pressure Compensator
Starting Engine or No Load On System
When the engine is not running, spring (5) forces retainer (4) and spool (2) to the left. Bias spring (8) forces swashplate (9) against actuator (7). The tension of the bias spring holds the actuator against stroke limiter (16).When the engine is first starting, the pump is at the maximum displacement. Piston (11) (one of nine pistons) pumps hydraulic oil through valve plate (14) to pump outlet port (15). Some of the hydraulic oil flows through pilot passage (1) to spool (2).Hydraulic oil acts against spool (2) in order to move the spool to the right. The spool contacts the spring retainer (4). The force of the pilot oil against the spool is greater than the resistance of spring (5). The force causes the retainer and the spring to move to the right.When the spool moves to this position, control passage (17) is open to pilot pressure (1). Pilot oil can flow down the control passage and into stroke control actuator (7). The force of the pilot oil against the stroke control actuator overcomes bias spring (8) in order to destroke swashplate (9). Actuator (7) moves to the right until vent port (13) is open. When port (13) is open, excess pilot oil flows into the pump case. At this point, the swashplate is at a minimum angle and the pump displacement is at the minimum.When there is no load on the system, the minimum position provides oil in order to compensate for leakage in the auxiliary system.The swashplate remains in this position until the system load requires more flow. When the system load increases, the pump control upstrokes the swashplate.Upstroking
When the engine is running and the pump displacement is less than the load on