HOUSING 2451504 - Caterpillar

The Retarder Air Control Valve Is In The ON Position
Illustration 6 g00891626
The engine is operating. The parking brake reset valve is closed. The parking brake air control valve is in the OFF position. The secondary brake air control valve is in the OFF position. The retarder air control valve is in the ON position.
(2) Primary air tank
(18) Secondary brake and parking brake pressure switch
(23) Brake air relay valve
(24) Brake air relay valve for the Automatic Retarder Control (ARC)
(25) Double check valve
(26) Front brake cooling diverter valve
(27) Stop lights pressure switch
(28) Service brake and retarder pressure switch
(30) Front brake master cylinders
(31) Rear brake master cylinders
(32) Retarder air control valve
(33) Manual retarder pressure switch Note: The darkened lines show air pressure and the arrows show the direction of flow.Note: Air pressure switches (28), (27), and (33) are activated when the retarder is applied.Note: Secondary brake and parking brake pressure switch (18) is deactivated when the parking brake air control valve and the secondary brake air control valve are in the OFF position. The parking brakes are released.When the lever for retarder air control valve (32) is in the ON position, air pressure from primary air tank (2) flows through retarder air control valve (32) and through three double check valves (25). Some of this air flows through double check valve (25) to front brake cooling diverter valve (26). Air pressure at front brake cooling diverter valve (26) causes oil to flow through the front brake oil cooler. The rest of the air pressure flows through double check valve (25) to the control passage of brake air relay valve (23). This allows supply air from primary air tank (2) to flow through brake air relay valve (24) to front brake master cylinders (30) and to rear brake master cylinders (31). The double check valve that is above the brake master cylinders closes the passages to brake air relay valve (24) for the Automatic Retarder Control (ARC). Oil pressure from the brake master cylinders flows to the wheel brakes. The oil pressure activates the brakes. The engine speed must be kept between 1500 rpm and 1900 rpm in order to keep the oil to the brakes cool.
Do not increase speed while the retarder is ON.
The pressure of the air to the brake master cylinders is determined by the position of the lever for the retarder air control valve. When the lever is completely pulled down, the maximum amount of retarding is achieved.When retarder air control valve (32) is in the OFF position, the flow of air through retarder air control valve (32) is blocked. Air pressure between the control passages of brake air relay valve (23) and retarder air control valve (32) flows outward through an exhaust passage in retarder air control valve (32). The air pressure between brake air relay valve (23) and the brake master cylinders flows outward through an exhaust passage in the brake air relay valve (23). The oil pressure that had applied the brakes returns to the brake