Mixer taps or valves

Claim 1

A mixer tap or valve for hot and cold water supplies comprising a housing having an inner surface defining a cylindrical chamber; laterally disposed inlet ports for the respective supplies, said inlet ports being spaced apart in the longitudinal direction of said chamber and communicating therewith; at least one outlet port for said supplies or a mixture thereof communicating with said chamber; a cylindrical piston arranged for rotation and reciprocation in said chamber and movable axially between an open and a closed position; passage means in said piston for providing communication between said inlet ports and said at least one outlet port and adapted to cooperate with said inlet ports so as to select or mix the supplies and to control the volume thereof; and sealing means between said piston and said surface and comprising a plurality of axially spaced coaxially disposed annular sealing members located respectively in annular grooves in said piston and bearing with sliding and sealing engagement against said surface, one of said sealing members being arranged in such a manner aS to be located always between the two inlet ports without overlapping either of the same in open as well as in closed position of the valve and at least one other of said sealing members being located with a slight stretch fit in its groove to prevent said at least one other sealing member to bulge locally unduly into the associated inlet port, said at least one other sealing member being positioned to move at least partially across at least one of said inlet ports upon axial movement of said piston to said closed position, the arrangement being such that surge pressure occurring upstream of said other annular sealing member at the instant of closure acts on the transverse projected area thereof in the same axial direction as that in which the piston is moved to close the valve.