SPACER 2106765 - Caterpillar

Illustration 1 g00284661
Location of the service brake air control valve
The service brake air control valve is a foot operated control valve. When the pedal is pushed, modulated air pressure is sent from the primary air tank to the brake air relay valve.The body of the service brake air control valve acts as a manifold. Air supply from the primary air tank to some of the other air control valves flows through the body of the service brake air control valve.
Illustration 2 g00295390
(1) Valve seat
(2) Rubber spring
(3) Piston assembly
(4) Retainer
(5) Outlet passage
(6) Spring
(7) Valve seat
(8) Valve seat
(9) Valve
(10) Valve body
(11) Spring
(12) Exhaust passage
(13) Inlet passage
(14) Exhaust diaphragm When the brake pedal is pushed, a force is put on valve seat (1). This force pushes rubber spring (2) and piston assembly (3) downward. Valve seat (7) blocks exhaust passage (12) in valve (9). Piston assembly (3) moves valve (9) off valve seat (8). Pressure air from inlet passage (13) flows around valve (9) to outlet passage (5). The air then flows out of the service brake air control valve to the brake air relay valve.When the air pressure below piston assembly (3) becomes higher than the pressure due to the brake pedal, piston assembly (3) lifts up enough to allow valve (9) to move up to valve seat (8). This stops the supply of pressure air to outlet passage (5). Piston assembly (3) is still in contact with valve (9), so exhaust passage (12) is also closed. Now, the pressures inside the service brake control valve are in balance. Air pressure is blocked in the air lines.When the brake pedal is lifted by a small amount, the force above piston assembly (3) is reduced. The pressure air below piston assembly (3) and the force of spring (6) will lift piston assembly (3) off valve (9). Pressure air from the air lines will flow around piston assembly (3) and through exhaust passage (12). The air from exhaust passage (12) leaves the service brake control valve through exhaust diaphragm (14). Air will exit the service brake control valve until the pressures are balanced.When the brake pedal is completely released, piston assembly (3) moves off valve (9). Air pressure flows through exhaust passage (12) to exhaust diaphragm (14). Valve (9) is held against valve seat (8) by spring (11).