Relay Valve

Description: The relay valve is an air-operated valve. It is used in air brake system to remotely control the brakes at the rear of a heavy truck or semi-trailer in a tractor-trailer combination. Their purpose is to speed up both the application and release of the service brakes. Working Principle: Within a braking process, the compressed air from the brake valve flows into chamber (A) via port 4. When the pressure in chamber (A) is increased, piston (7) is pushed downwards and the outlet valve (6) is closed. As the piston continues its downward motion, inlet valve (3) opens. The compressed air in port 1 thus flows across the opened inlet valves (3) into port (2) and from there to the connected brake cylinders. When the brakes are released, the compressed air below the piston in port (2) is stronger than the compressed air in port (4) and the piston moves upwards until a balance of forces has been achieved. The bell-shaped valve follows and closes the inlet valve (5). The relay valve thus has reached a final braking position. .