VALVE CARTRIDGE FOR LIFT VALVE HAVING THE CLOSING PRESSURE ON THE SEALING LIMITED

Valve cartridge (10) includes a housing (32) having inlet member (54), outlet member (52) and screw thread (34). Cavity (36) extends axially through housing (32) within which is a piston (38) which moves axially against piston seal (44) to open and close tap (10). A flow chamber (40) is provided at the end of housing (32) and includes a first seal (42) for sealing against a valve seat (18) in the tap (10). Piston (38) can be moved axially by either a rotatable spindle (46) or, a solenoid (48) and push rod (50). Piston (38) is moved axially without any rotation. Coupling member (84) couples spindle (46) to piston (38) and rotates relative to the piston (38) and the spindle. When spindle (46) is turned a predetermined number of revolutions the coupling (84) causes piston (38) to abut piston seal (44), any further rotation of spindle (46) causes rotation of the coupling member (84) without effecting the axial position of piston (38). Ratchet members (92, 94), slip past housing splines (102) when the predetermined number of revolution or force is reached. This limits the sealing pressure of the piston (38) against the piston seal (44) irrespective of the number of turns made of spindle (46). Stops (64) limits maximum opening and prevents check valve (70) from being forced into sealing contact with inlet member (54).