A valve cartridge has a hollow housing having an open end, a floor plate closing the open end and formed with a plurality of throughgoing ports each having an inner surface, a valve plate in the housing fixed atop the floor plate and formed with holes aligned with the floor-plate ports, a movable valve plate in the housing atop the fixed valve plate and formed with a cavity, and an actuating element connected to the movable valve plate for displacing the movable valve plate on the fixed plate and shifting the cavity into and out of engagement with the fixed-plate holes so that if one of the holes is supplied with water under pressure the actuating element can control flow from the one hole to the other hole. Respective annular seal rings made of an elastomeric plastic are received in the ports, formed in situ in the ports, and have outer surfaces bonded to the inner surfaces of the respective ports. The floor plate is made of a material that can bond to and slide relative to the plastic of the seal rings.