VALVE GP-NEUTRALIZER 4T3128 - Caterpillar

Illustration 1 g01249802
The service brake control valve is located under the service brake pedal in the operators station.The service brake control valve is actuated by depressing the service brake pedal in the operators station. When the brake pedal is depressed, a roller on the pedal assembly actuates the service brake control valve.The service brake control valve is a dual pressure reducing valve with two independent output pressures.
Illustration 2 g00880683
Service brake control valve (B) Service brake ports (C) Pressure ports (from accumulators)Modulation of the pressurized oil in the accumulators to the service brakes is controlled by the service brake control valve. 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 brakes also change.
Illustration 3 g00880685
View (A-A) of the service brake control valve (1) Piston (2) Spring (3) Spring (4) Spring (5) Retainer (6) Ball (7) Spacer (8) Upper valve spool (9) Plug (10) Outlet to the rear brakes (11) Passage (12) Drain port to tank (13) Supply from accumulator for the rear service brakes (14) Upper valve spool passage (15) Cavity (16) Lower valve spool (17) Outlet to tank (18) Outlet to front service brakes (19) Passage (20) Lower valve spool passage (21) Supply from accumulator for the front service brakes (22) Spring (23) CavityWhen the operator pushes on the brake pedal, a roller on the brake pedal assembly forces piston (1) downward. Piston (1) applies 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 spool (8) to move away from the seat in spacer (7) .The movement of upper valve spool (8) causes the movement of the lower valve spool (16) and the compression of spring (22). When valve spools (8) and (16) move, oil flow through passages (11) and (19) to the hydraulic tank is blocked.This allows pressurized oil from accumulator ports (13) and (21) to flow through passage's (11), (14), (19) and (20). The oil then flows through passages (10) and (18) in order to apply 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 springs (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) and causes accumulator ports (13) and (21) to be covered. The level of