789D and 789D XQ Off-Highway Truck Air System and Brakes: Air Control Valve (Service Brake)

Location of the service brake air control valve

(2) Supply port(3) Exhaust port

The service brake air control valve is a foot operated control valve. When the pedal is pushed, modulated air pressure is sent from the service brake and retarder air tank to the brake air relay valve.
Air supply from the service brake and retarder air tank flows into the supply port (2). As the pedal is depressed, the exhaust port (3) closes. The service brake control valve allows air from supply port (2) to flow through outlet port (1). The position of the pedal allows the valve to modulate the outlet pressure that flows to the brake air relay valve. When the pedal is released, the outlet pressure is discharged through exhaust port (3).

Air Control Valve (Secondary Brake)

Location of the secondary brake air control valve

(2) Supply port(3) Exhaust port

The secondary brake air control valve is a red foot-operated secondary brake control. When the pedal is pushed, modulated air pressure is sent from the parking and secondary brake air tank to the secondary brake inverter valve.
Air supply from the parking and secondary brake air tank flows into the supply port (2). As the pedal is depressed, the exhaust port (3) closes. The secondary brake air control valve allows air from supply port (2) to flow through outlet port (1). The position of the pedal allows the valve to modulate the outlet pressure that flows to the secondary brake inverter valve. When the pedal is released, the outlet pressure is discharged through exhaust port (3).

Air Control Valve (Parking Brake)

Location of the parking brake control valve for the air(2) Parking brake lever

The parking brake control valve for the air is located in the control console. The parking brake control valve controls the air flow to the parking and secondary brake valve.

(1) Plunger (2) Lever (3) Passage in plunger (4) Exhaust passage (5) Delivery passage (6) Spring (7) Inlet valve (8) Valve seat (9) Spring(10) Supply passage

When lever (2) is in the OFF position, lever (2) pushes down on plunger (1). Plunger (1) moves inlet valve (7) off valve seat (8). Plunger (1) also blocks exhaust passage (4). Air pressure from supply passage (10) flows around inlet valve (7) to delivery passage (5) .
Air flows out of delivery passage (5) to the parking and secondary brake valve. The air flow pushes down a spool in the parking and secondary brake valve. This allows oil flow to release the spring applied parking brakes.
When lever (2) is moved to the ON position, lever (2) releases plunger (1). Spring (6) raises plunger (1) off inlet valve (7). Spring (9) pushes inlet valve (7) against valve seat (8). The air flow from supply passage (10) is blocked. Delivery passage (5) remains open. The air from the parking and secondary brake valve flows through passage (3) in plunger (1). This air exits the parking brake control valve through exhaust passage (4) .
When air supply to the parking and secondary brake valve is shut off, a spring in the parking and secondary brake valve moves the spool. This stops the oil flow to the chamber for the parking brakes. The parking brakes will now engage.

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789D and 789D XQ Off-Highway Truck Air System and Brakes: Air Control Valve (Service Brake) 2013-01-25T20:35:00-08:00 Rating: 4.5 Diposkan Oleh: Unknown