Non-leak valve of plastic construction

Claim 1

In a valve, the combination comprising a. a molded plastic chamber including a body and a cap removably carried thereby, there being an annular main seat in the body and a chamber outlet from the body, b. a stem projecting generally coaxially through the seat with clearance therefrom, and toward the cap at one side of the seat, c. a stopper carried by the stem to engage and disengage the seat at the opposite side thereof in response to axial bodily displacement of the stem, d. structure carried by the cap and carrying the stem to effect said displacement thereof, and e. the chamber having a liquid pressure inlet to communicate said pressure to the stopper for transmitting pressure loading to the seat when the stem is displaced with consequent engagement of the stopper against the seat, whereby the stopper will remain closed against the seat irrespective of liquid pressure or temperature change induced expansion or contraction of the housing, f. said structure including an actuator piston movable in response to liquid pressure application thereto to effect stem displacement in a direction to disengage the stopper from the seat, and means to cOntrol liquid pressure communication to said piston via a passage within the stopper and stem and to which liquid pressure at the inlet side of the seat has access.