HARNESS AS-CONTROL 3780741 - Caterpillar

ACCUMULATOR CHARGING VALVE (OIL FLOW TO ACCUMULATOR)
1. Passage. 2. Spring. 3. Retainer. 4. Detent balls (nine). 5. Check valve. 6. Outlet to accumulator. 7. Charging valve spool. 8. Springs. 9. Shims. 10. Shims. 11. Piston. 15. Orifice. 16. Passage. 17. Inlet from pump. 19. Flow control valve spool. 24. Radial holes. 25. Outlet to pilot system.Relief Valve Operation
The relief valve controls maximum oil pressure in the accumulator if the charging valve spool does not move to the CUTOUT position. The relief valve (13) opens and oil from chamber (23) goes to tank through outlet (21). This lowers the pressure in chamber (23) and valve spool (19) moves to the left against spring (22). The flow of oil then goes through holes (26) to outlet (25).
RELIEF VALVE OPERATION
7. Charging valve spool. 11. Piston. 12. Passage. 13. Relief valve. 14. Orifice. 18. Shims. 19. Flow control valve spool. 20. Spring. 21. Outlet to hydraulic tank. 22. Spring. 23. Chamber. 25. Outlet to pilot system. 26. Radial holes.The addition or removal of shims (18) changes the force of the spring (20) on the relief valve (13). The addition of shims causes an increase in the opening pressure of the valve (13).Leakage past piston (11) and charging valve spool (7) goes through passage (12) and back to tank through outlet (21).Accumulator
ACCUMULATOR OPERATION
1. Nitrogen charging valve. 2. Accumulator. 3. Nitrogen gas chamber. 4. Piston. 5. Pressure oil chamber. 6. Outlet to brake control valve.The accumulator is on the left side of the machine below the left hand service center door. It has a sealed piston (4) that moves up and down inside the bore of the accumulator. The chamber (3) above the piston has a charge of dry nitrogen gas. The charge of dry nitrogen gas is put into the accumulator through the valve (1). Oil from the pump and accumulator charging valve comes through port (6) into the chamber (5). This oil pushes the piston (4) up and causes compression of the dry nitrogen gas. When the pressure in the accumulator gets to about 1950 psi (13 400 kPa), the supply of oil is stopped by the accumulator charging valve. When either brake pedal is pushed, oil from the chamber (5) goes out port (6) to the brake control valve to activate the brakes.Brake Control Valve
Modulation of the high pressure oil in the accumulator to the wheel brakes is controlled by the brake control valve. The position of the brake pedal causes a specific pressure at the brakes. As the position of the pedal changes, the pressure at the brakes changes.
BRAKE CONTROL VALVE
1. Orifice check valve. 2. Spring. 3. Outlet to wheel brakes. 4. Valve spool. 5. Springs. 6. Plunger. 7. Piston. 8. Inlet, (supply from accumulator). 9. Return outlet for neutralizer valve. 10. Shims.When either brake pedal is pushed, linkage from the pedal moves the plunger (6). The plunger puts a force on the springs (5). The force of the springs (5) moves the valve spool (4) and causes compression of