| 摘要 |
A back flow preventer valve assembly for protecting fluid supply systems against back flow of contaminating fluids includes a pair of serially connected check valves positioned within respective housings which are connected together and to inlet and outlet fittings by slidable sleeve-type couplings. The couplings are sealed to the fittings and to the valve housings by resilient annular gaskets, preferably O-rings. Tie bolts extend longitudinally from the inlet fitting coupling to the outlet fitting coupling to retain the assembly together. This assembly provides for interchangeability of components, easy removal of the valve units from the line in which they are connected without disconnection of the inlet and outlet fittings, and for easy replacement or substitution of a fitting. Each check valve includes a poppet assembly of advantageous modular construction, with components easily replaceable. In one form of the invention, a venting valve is connected between the two valve housings to relieve any pressurized fluid which might leak back through the downstream check valve when inlet fluid pressure is below the threshold pressure of the first check valve. The venting valve includes a cylindrical resilient diaphragm-type valve closure member which shuts off the venting valve whenever inlet line pressure is above the threshold pressure of the first check valve. The venting valve serves to provide, in addition to the tandem check valves, a third safety feature preventing infiltration of back flow into the inlet line.
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