Relay valves are a special type of relay used in air brake systems to speed up the application and release of the brakes. They are typically mounted close to the chambers they serve and are available in both remote and reservoir mount designs.
The relay piston 16 is slidably received within the primary bore defined within the housing 12. Secondary bore 30 is counterbored as at 32. The counterbore 32 slidably receives a load piston 34 which cooperates with the housing 12 to define a load volume 36 therebetween. The load piston 34 is urged upward by a spring 42 which exerts a force slightly larger than the load volume 36 at a predetermined supply pressure to yield the relay piston 16 which carries a circumferentially extending inlet/exhaust valve 56, a sealing surface 58 and an inlet/exhaust spring 60.
As the relay piston 16 rises, the spring 42 yields and a portion of the surface 70' of the inlet/exhaust valve member 56 is brought into sealing engagement with the sealing surface 58, thereby closing off communication between the inlet port 38 and outlet port 24 through the volume 22. As viewed FIG. 2, the exhaust valve seat 64 carded by the piston 16 is lifted off the sealing surface 58 to permit high pressure at the outlet port 24 and in the volume 22 to vent to atmosphere through the exhaust port 52.
Relay valves are a special type, and are not to be confused with normal switches. Relay valves are electromagnetically induced current converters that convert electrical inputs into currents up to 100 amps or more. Relays are used for many purposes, including powering small devices, converting low voltage to high current, switching large machines and controlling multiple circuits at once.
