Plug valve

Claim 1

A plug valve, the plug valve comprising in cooperative combination a valve body, the body having a first end and a second end, a fluid passageway extending from the first end to the second end, a plug receiving cavity defined by the body with the plug receiving cavity extending generally normally to the axis of the fluid passageway extending from the first end to the second end; a plug disposed within the passageway, the plug having a stem, the stem extending away from said valve body, the valve body and the plug having a synthetic resinous coating thereon, a generally planar seal member disposed over said plug adjacent the stem, a bonnet disposed over said seal member, said bonnet being affixed to the valve body and forcing said sealing member in sealing engagement with the valve body, said bonnet defining a generally centrally disposed stem receiving passageway of a diameter substantially greater than the diameter of the stem; a gland adjustably positionable on said bonnet and extending into the passageway of the bonnet about the stem, the improvement which comprises said plug at a location adjacent the juncture of the plug and the stem defining an annular frustoconical surface having its major diameter adjacent said plug and its minor diameter adjacent said stem; said seal member defining a generally centrally disposed opening therein of sufficient diameter to pass over said stem, the opening being defined by a flexible annular seal portion which when the seal is positioned against the plug, the flexible annular seal portion conforms to the annular frustoconical surface, a retaining ring having an inside diameter approximating the major diameter of the frustoconical surface; a cup seal of annular configuration having a trapezoidal cross section disposed against the sealing member and having a face generally parallel to the frustoconical surface, the cup seal being restrained from radial movement by said annular retaining ring, said cup seal being of a pressure deformable synthetic resinous material, a rigid annular cup seal support ring disposed adjacent said cup seal and remote from said plug; means to resiliently tension the cup seal support ring toward said plug to thereby provide a plug valve with a reduced tendency to leak and desirable service life.