Brake pressure control valves for split braking systems

Claim 1

A valve assembly for use in a vehicle braking system, having separate wheel brakes and separate pressure sources, comprising first and second valves having respective inlets for connection to said separate pressure sources and respective outlets for connection to said separate wheel brakes, wherein each valve includes a movable valve part carried by an associated pressure responsive member, a stationary valve part cooperating with the movable part to control communication between the inlet and outlet, said stationary valve part being stationary at all times, and biasing means applying a biasing force urging said pressure responsive member in a direction to maintain its valve open, and wherein each said pressure responsive member is stepped and has opposed piston portions of different dimensions, both being subjected to the pressure at the inlet of its associated valve to produce a net effect tending to close that said valve in opposition to said biasing means, and has a further stepped diameter portion directly subjected to the inlet pressure of the other said valve to produce an additional force on said pressure responsive member, said additional force acting independently of the biasing force of the biasing means of said other valve and said additional force being removed upon failure of the inlet pressure of said other valve.