Control valve assemblies for vehicle anti-skid braking systems

A control valve assembly for a vehicle hydraulic braking system comprising a housing having an inlet port for connection to a supply of hydraulic fluid under pressure, an outlet port for connection to a wheel brake, and a pressure-relief port for connection to a reservoir for fluid, said housing having a first chamber, valve means in said first chamber movable between a first position in which said inlet port is in communication through said chamber with said outlet port and communication between said chamber and said pressure-relief port is closed, and a second position in which communication between said inlet port and said chamber is cut-off and said outlet port is in communication through said chamber with said pressure-relief port, and resilient means for urging said valve means into said first position, said housing having a stepped bore and a second chamber, communicating means between said second chamber and said first chamber open at least when said valve means is in said first position, a differential piston working in said stepped bore in said housing and having opposite ends of greater area and of smaller area, said end of greater area being exposed to said inlet port and said end of smaller area being exposed to said second chamber, said piston having a restricted passage through which said inlet port communicates at all times with said second chamber, said second chamber being located in said housing between said smaller diameter end of said piston and an adjacent inner end of said stepped bore.