CYLINDER GP-THUMB 4427956 - Caterpillar

Note: The darkened lines show air pressure and the arrows show the direction of air flow.Note: Air pressure switches (19) and (20) are activated when the service brakes are applied or when the retarder is used.Note: Parking and secondary brake pressure switch (31) is deactivated when the air control valve (parking brake) and the air control valve (secondary brake) are in the OFF position. The parking brakes are released.When the pedal on service brake air control valve (12) is pushed down, air pressure from air tanks (service brakes and retarder) (5) flows through service brake air control valve (12). The air pressure flows to the control passage of rear brake air relay valve (23). This allows supply air from air tanks (service brakes and retarder) (5) to flow through rear brake air relay valve (23) to air/hydraulic cylinder (18) for the rear brakes. Double check valve (45) above the air/hydraulic cylinder closes the passages to brake air relay valve (44) for the Automatic Retarder Control (ARC). Oil pressure from the air/hydraulic cylinder flows to the service brakes for the rear wheels. The oil pressure activates the service brakes for the rear wheels.The air pressure that flows through service brake air control valve (12) also flows to front brake air control valve (21). When the front brake air control valve is in the ON position, air flows to front brake air relay valve (15). This allows supply air from air tanks (service brakes and retarder) (5) to flow through front brake air relay valve (15) to air/hydraulic cylinder (17) for the front brakes. Oil pressure from the air/hydraulic cylinder flows to the front caliper service brakes. The oil pressure activates the front caliper service brakes.When the pressure on the pedal of service brake air control valve (12) is released, the flow of air through the service brake air control valve is blocked. Air pressure between the control passages of brake air relay valves (15) and (23) and service brake air control valve (12) flows outward through an exhaust passage in service brake air control valve (12). The air pressure between brake air relay valves (15) and (23) and air/hydraulic cylinders (17) and (18) flow outward through an exhaust passage in the brake air relay valves. The oil pressure that had applied the brakes returns to the air/hydraulic cylinders as the pistons are drawn up by the spring in the air/hydraulic cylinders.The Retarder Air Control Valve Is in the ON Position
Illustration 8 g01018179
AGC991-1403 Truck with standard front oil cooled service brakes AGY1-199 Truck with standard front oil cooled service brakes (no air start attachment) (5) Air tanks for the service brakes and the retarder (10) Double check valve (13) Manual retarder pressure switch (14) Retarder air control valve (15) Brake air relay valve (17) Air/hydraulic cylinder (front) (18) Air/hydraulic cylinder (rear) (19) Service brake and retarder pressure switch (20) Stop lamp air pressure switch (31) Parking and secondary brake pressure switch (44) Brake air relay valve for the Automatic Retarder Control