CHANNEL A- 0540186 - Caterpillar

Illustration 1 g02462176
Left pedal service brake control valve
The service brake control valve is on the front left side, and underneath the operators platform.
Illustration 2 g00274835
Left pedal service brake control valve
(B) Service brake ports. (C) Pressure ports.
Illustration 3 g03648345
Service brake Valve not activated
View A-A of the service brake control valve
(1) Piston
(2) Spring
(3) Spring
(4) Retainer
(5) Ball
(6) Spacer
(7) Upper valve spool
(8) Outlet to rear service brake
(9) Outlet to hydraulic tank
(10) Passage
(11) Supply from accumulator for rear service brakes
(12) Drain port to tank
(13) Upper valve spool passage
(14) Cavity
(15) Lower valve spool
(16) Plugged port
(17) Outlet to front service brakes
(18) Passage
(19) Lower valve spool passage.
(20) Supply from accumulator for the front service brakes
(21) Cavity
(22) Spring
Illustration 4 g03648347
Service brake valve activated
View A-A of the service brake control valve
(1) Piston
(2) Spring
(3) Spring
(4) Retainer
(5) Ball
(6) Spacer
(7) Upper valve spool
(8) Outlet to rear service brake
(9) Outlet to hydraulic tank
(10) Passage
(11) Supply from accumulator for rear service brakes
(12) Drain port to tank
(13) Upper valve spool passage
(14) Cavity
(15) Lower valve spool
(16) Plugged port
(17) Outlet to front service brakes
(18) Passage
(19) Lower valve spool passage.
(20) Supply from accumulator for the front service brakes
(21) Cavity
(22) SpringThe 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 either brake pedal causes a specific pressure at the service brakes. As the position of the pedal changes, the pressure at the service brakes also changes.When one of the brake pedals is depressed, a roller in the brake pedal assembly pushes down on piston (1). Piston (1) applies a force on springs (2) and (3). The force of springs (2) and (3) moves retainer (4) and ball (5). Movement of retainer (4) and ball (5) causes upper valve spool (7) to move away from the seat in spacer (6).The movement of upper valve spool (7) causes the movement of lower valve spool (15) and the compression of spring (22). When valve spools (7) and (15) move, the oil flow through passages (10), (12), and (18) to the hydraulic oil tank is blocked.This spool movement allows pressurized oil from accumulator ports (11) and (20) to flow through passages (10), (13), (18), and (19). The oil then flows through passages (8) and (17) to apply the service brakes. At the same time, pressurized oil flows into cavities (14) and (21), and through passages (13) and (19). The oil pressure at the service brakes has the same pressure as the oil in cavities (14) and (21).Oil pressure in cavity (21) and the force of spring (22) act to balance lower valve spool (15) against the pressure in cavity (14). In the same manner, pressure in cavity (14) creates a force against the bottom of upper valve spool (7). The upper valve spool is balanced by the force of spring (2) at the top of spool (7).The force of springs (2) and (3) is balanced by the force that is applied to the pedal. Upward movement of valve spools (7) and (15) causes accumulator ports (11) and