Check valve assembly for use in backflow preventers or the like

Claim 1

A check valve to prevent backflow in a system comprising: a body member having a flow passage therethrough with an inlet and an outlet, said body member further having an annular valve seat in said passage and an opening through its wall opposite and coaxial with said valve seat; a tamperproof pre-loaded valve module inserted as a unit through said opening for coacting with said valve seat and removable as a unit; a cover plate for retaining said valve module in position in said body member; said module including a valve disc having a valve stem extending from one side thereof with the other side having a seal element for coacting with said valve seat, a spring retainer, said spring retainer having a tapered cup-shaped body with an annulus at one end for receiving said valve stem therethrough and a radial outwardly extending flange at the other end having a diameter to fit within said opening, a coil spring extending between said flange of said spring retainer and said valve disc, and a retaining nut carried on the end of said valve stem within said tapered body to provide a preload on said spring, said retaining nut being threaded onto said valve stem and seated against said annulus of said spring retainer when said coil spring is compressed and prior to insertion of said module into said body member, said module having an overall length between said seal element and said flange of said spring retainer greater than the overall length between said valve seat and said opening whereby when said module is inserted into said body member onto said valve seat, said cover plate is installed, said spring retainer slides on said valve stem and applies a further load on said spring; and means to prevent inadvertent unthreading of said nut when said module is removed from said valve body until said spring is compressed, said means for preventing inadvertent unthreading of said nut including bosses provided on the interior of the tapered cup-shaped body adjacent the end having the annulus, said bosses being positioned closely adjacent to the periphery of said nut whereby a conventional tool cannot be placed on said nut unless said spring is compressed to cause said valve stem to move relative said spring retainer to lift said nut away from said annulus and said bosses.