GASKET-VALVE COVER 2784693 - Caterpillar

Illustration 1 g00903288
Location of Service Brake Control ValveThe service brake control valve is located on the right side of the hydraulic oil tank in the engine compartment. The service brake control valve is positioned below the accumulator charging valve.When the brake pedal is depressed, a roller on the cross shaft assembly actuates the service brake control valve. The control valve is a dual pressure reducing valve with two independent output pressures.
Illustration 2 g00902496
Service Brake Control Valve (B) Service brake ports. (C) Pressure ports (accumulators).
Illustration 3 g00902497
(1) Piston (2) Spring (3) Spring (4) Spring (5) Retainer (6) Ball (7) Spacer (8) Upper valve spool (9) Tank port (10) Outlet to rear service brakes (11) Passage (12) Drain port (13) Accumulator pressure (rear service brakes) (14) Upper valve spool passage (15) Cavity (16) Lower valve spool (17) Tank port (18) Outlet to front service brakes (19) Passage (20) Lower valve spool passage (21) Accumulator pressure (front service brakes) (22) Spring (23) CavityThe service brake control valve modulates the flow of pressurized oil. The flow of pressurized oil is modulated between the brake accumulators and the service brakes. The position of the brake pedal causes a specific pressure at the service brakes. As the position of the pedal changes, the pressure at the service brake also changes.When the brake pedal is depressed, the roller on the pedal assembly pushes piston (1) downward. Piston (1) applies a force on springs (2), (3) and (4). The force of springs (2) and (3) moves retainer (5) and ball (6). Movement of retainer (5) and ball (6) causes upper valve spool (8) to move away from the seat in spacer (7) .The movement of upper valve spool (8) causes the movement of lower valve spool (16) and the compression of spring (22). When valve spools (8) and (16) move, oil flow through passages (11), (12) and (19) to the hydraulic oil tank is blocked.This allows pressurized oil from accumulator ports (13) and (21) to flow through passages (11), (14), (19) and (20). The oil then flows through passages (10) and (18) in order to engage the service brakes. At the same time, pressurized oil flows into cavities (15) and (23), and through passages (14) and (20). The oil pressure at the service brakes has the same pressure as the oil in cavities (15) and (23) .Oil pressure in cavity (23) and the force of spring (22) act to balance lower valve spool (16) against the force of the pressure in cavity (15). In the same manner, pressure in cavity (15) creates a force against the bottom of upper valve spool (8). The upper valve spool is balanced by the force of spring (2) and (3) at the top of spool (8) .The force of springs (2), (3) and (4) is balanced by the force that is applied to the pedal. Upward movement of valve spools (8) and (16) causes accumulator ports (13) and (21) to be covered. The level of pressure in the independent valve sections creates a