Abstract: The relay valve employs a body preferably of metal defining a central exhaust port and a pair of delivery ports on the bottom of the valve body as well as a supply port on the side thereof. The body defines a cylinder in which a spool or shuttle moves toward and away from the exhaust port. A cover seals the upper open end of the body and defines a second cylinder in which a large piston moves from an upward, non operative position to a lower, operated position in engagement with the spool. The cover includes a control line port through which control pressure is applied to the valve. Service brake delivery pressure for the brake system is available at the supply port of the relay valve and sealed from the two or more delivery ports by a pair of O rings sealing the spool to shuttle in the body.

Abstract: A brake system for a vehicle having two sets of brakes, a front set and a rear set of brakes and including a source of fluid pressure, a driver controlled valve, in which the sets of brakes respond to fluid pressure from said source via said driver controlled valve, including a secondary valve having at an input port a connection to the driver controlled valve and its output port coupled to the rear brakes, and in which the secondary valve means produces an increase in pressure at the output port above the pressure of the input port, in which the secondary valve including time delay means for reducing excess pressure at the outlet port to reduce the pressure at the outlet port to substantially the pressure at the inlet port after the application of pressure to the inlet port by operation of the driver controlled valve.