ALTERNATOR AS 3746762 - Caterpillar

Illustration 1 g00735000
(1) Brake air relay valve for the service brakes for the front wheels (2) Brake air relay valve for service brakes and for the manual retarder (3) Double check valve (4) Front brake inverter valve (5) Double check valveThe brake air relay valves are located on the inboard side of the frame on the left side. Brake air relay valve (1) activates the front air/hydraulic cylinder when the service brake pedal is applied. The front brake control must be in the ON position. Brake air relay valve (2) activates the rear air/hydraulic cylinder when the service brake pedal, or the manual retarder control is applied.When the service brake pedal is pushed with the front brake control in the ON position, signal pressure is sent to the control passage of brake air relay valve (1). This causes an internal valve in brake air relay valve (1) to open. This allows air from the air tanks for the service brakes and the retarder to flow through brake air relay valve (1). This air flows to the air chamber of the front air/hydraulic cylinder. The front air/hydraulic cylinder then engages the brakes for the front wheels.When the service brake pedal is pushed or when the manual retarder is used, signal pressure is sent to the control passage of brake air relay valve (2). This causes an internal valve in brake air relay valve (2) to open. This allows air from the air tanks for the service brakes and the retarder to flow through brake air relay valve (2). This air flows to the air chamber of the rear air/hydraulic cylinder. The rear air/hydraulic cylinder then engages the service brakes for the rear wheels.Brake air relay valves (1) and (2) all release in the same way. When the brake pedal is released or when retarding is not needed, the signal pressure to the control passage of the brake air relay valve will stop. The internal valve in the brake air relay valve will shift in order to block the flow of air from the air tanks for the service brakes and the retarder. When the front and rear air/hydraulic cylinders do not receive air flow to the air chambers, the brakes are released.Double check valve (3) allows brake air relay valve (2) and the service brake air control valve to share the same air lines to the rear air/hydraulic cylinder. Double check valve (5) allows brake air relay valve (1) and front brake inverter valve (4) to share the same air lines to the brake master cylinder for the front wheels.Front brake inverter valve (4) is used to engage the front brakes when the secondary brake pedal is pressed. Front brake inverter valve (4) will engage the front brakes even if the front brake control is in the OFF position.