Abstract: A lightweight, non-metallic valve is preferably formed of molded plastic. The valve has an hour-glass configuration or enlarged recesses formed therein to reduce the overall mass of the assembly and provide increased sensitivity to low flow rates. Sealing O-rings are snap fit into grooves at opposite ends of the symmetrical assembly.

Abstract: A relay valve for a fluid pressure braking system includes a relay piston and a load piston which is responsive to the pressure at the inlet port of the relay valve to exert a biasing force on the relay piston loading the latter against the inlet/exhaust valve. The biasing force is opposed by fluid pressure at the inlet port acting across the effective area of the inlet/exhaust valve. The biasing force is greater than the spring force holding the inlet/exhaust valve closed, so that the valve responds immediately to pressure signals transmitted through the control port of the relay valve.