COVER AS-HYDRAULIC TANK 2814551 - Caterpillar

Operation of Control Valve in HOLD position
FOUR POSITION CONTROL VALVE IN HOLD POSITION
2. Four position control valve. 6. Directional control spool. 7. Flow control valve. 8. Compensator spool. 9. Secondary shuttle. 10. Primary shuttle. 12. Metering holes. 13. Inlet chamber. 14. Hole. 15. Chamber. 16. Passage. 17. Passage to next (adjacent) control valve. The operation of the three position control valves is the same as the four position in the Port "A", Port "B" and HOLD position.With directional control spool (6) in the HOLD position, the pump will be in a low pressure standby condition. The pump oil pressure of 1380 kpa (200 psi) is sent to inlet chamber (13). Passage (16) is connected to the outlet side of primary shuttle (10). With directional control spool (6) in HOLD position, the inlet passages to primary shuttle (10) are open to tank. This lets the pump oil pressure move compensator spool (8) against the spring pressure until metering holes (12) are closed off. Oil pressure is then sent through hole (14), in flow control valve (7), into chamber (15) to passage (16) and then to tank. As oil pressure decreases, compensator spool (8) will move up and close hole (14). This action will decrease oil pressure felt at directional control spool (6) to approximately 690 kpa (100 psi) and will keep (maintain) this pressure at spool (6) even with other control valves in operation.Operation of Control Valve in Port "A" Position
FOUR POSITION CONTROL VALVE IN PORT "A" POSITION
2. Four position control valve. 6. Directional control spool. 7. Flow control valve. 8. Compensator spool. 9. Secondary shuttle. 10. Primary shuttle. 11. Kickout valve. 12. Metering holes. 13. Inlet chamber. 15. Chamber. 16. Passage. 17. Passage. 18. Shaft. 19. Passage. 20. Throttle opening. 21. Hole. 22. Passage. 23. Passage. 24. Detent balls. 25. Piston.When directional control spool (6) is moved to the Port "A" position, port oil pressure is immediately sent through passage (19) to primary shuttle (10). From primary shuttle (10) port oil pressure goes through passage (16) to chamber (15) and it also goes to secondary shuttle (9).Port oil pressure at chamber (15) goes through hole (21) to the spring chamber under compensator spool (8). If pump oil pressure at inlet chamber (13) is lower than port oil pressure, then compensator spool (8) moves up to its AT REST or LOAD CHECK position. This prevents oil pressure at Port "A" from decreasing while pump oil pressure increases.Port oil pressure at secondary shuttle (9) goes through a passage to the compensator valve on the pump and increases the pump oil pressure. If another control valve is in operation and has a higher port oil pressure, then port oil pressure in passage (17) will go to the pump compensator valve through the secondary shuttle.As pump oil pressure increases at inlet chamber (13), compensator spool (8) will move down to close (restrict) metering holes (12) until it makes (creates) a 420 kPa (60 psi) pressure drop across flow control valve (7) and