Fluid valve assemblies

Claim 1

A power control valve assembly for a vehicle braking system comprising a housing provided with first, second and third ports for connection respectively to a vehicle brake, a reservoir, and a fluid pressure source, a normally closed inlet valve controlling communication between said first and third ports, said inlet valve comprising an axially moveable inlet valve element and a relatively fixed inlet valve seat disposed between said first and third ports and being normally in engagement with each other so that communication between said ports is normally closed, a normally open exhaust valve controlling communication between said first and second ports, said exhaust valve comprising an axially moveable exhaust valve element and an axially moveable exhaust valve seat disposed between said first and second ports and being normally spaced apart from each other so that said first and second ports are normally in open communication with each other, said inlet valve being axially spaced from said exhaust valve, a passage extending axially between said inlet valve seat and a chamber which is at all times in open communication with said first port to provide fluid communication between said inlet valve seat and said chamber, an axially moveable control rod extending through said passage with clearance thoughout its length which permits fluid flow through said passage past said rod to said chamber, said rod having an axially extending end part of substantially uniform cross sectional area throughout its length and located in said passage adjacent said inlet valve for operating on said inlet valve element to control its position relative to said inlet valve seat, the other end of said control rod engaging with said exhaust valve, and an axially moveable valve actuating member acting on said exhaust valve and arranged to close said exhaust valve element against said exhaust valve seat and then to move said control rod until the end part thereof disengages said inlet valve element from said inlet valve seat, that part of said rod adjacent said end part being of reduced cross sectional area relative to said end part, the cross sectional area of said end part being of a size relative to said passage that during initial unseating of said inlet valve element said end part exerts a substantially constant throttling effect on flow through said passage.