A thermoplastic lined plug valve is prepared using a plug having a nonlocking taper and a stem at the small end of the plug. The plug is seated initially by forcing the plug into the plug cavity, raising the temperature of the plug valve above the service temperature of the valve body lining until the valve body lining conforms to the valve plug. Plug ValvesThe valve is then cooled to a temperature below the service temperature of the body lining. An improved method for the preparation of a plug valve, the steps of the method comprising providing plug valve body having a plug receiving cavity intermediate an entrance and exit port, the plug receiving cavity having a first region of lesser diameter and a second region of greater diameter, disposing within the body first and second rigid foraminous annular members, the members being disposed in the plug-receiving cavity, said first annular member being disposed in the region of lesser diameter and the second annular member being disposed in the region of greater diameter, embedding the annular members within a plastic lining thereby lining the plug receiving cavity and ports of the valve body,Globe Valves the plastic lining thereof having a service temperature, providing a plug suitable for use with the plug body, the plug being finished to a desired degree of taper, disposing the plug within the body, tensioning the plug into the plug-receiving cavity of the valve body, BUTTERFLY VALVESraising the temperature of the valve body and plug above the service temperature of the plastic lining of the valve body and forcing the plug into the cavity to thereby deform the liner of the valve body to conform to the valve plug and subsequently cooling body and plug below the service temperature of the valve body lining. In many applications piping is desired which has a lining of a generally chemically resistant synthetic resinous thermoplastic material. Usually, such lined conduits and lined piping systems are employed in applications where substantial mechanical protection is required and glass or plastic pipe would neither be safe nor suitable. Such lined piping systems are well known and frequently employ with benefit plastic-lined plug valves. Such plug valves usually comprise a plastic-lined cast iron or steel body and have a metal cored plug which is also plastic-coated and lined. Plug valves are generally a reliable shut-off means in a plastic-lined piping system. Such so-called plastic-lined plug valves have presented substantial problems over the years. Often, in order to obtain a desired degree of seating, auxiliary means have been employed to force a tapered plug into the plug-receiving cavity of the valve. Sometimes this is accomplished by means of a spring or bolt bearing directly or indirectly against the plug. Some plug valves, including plastic-lined plug valves, resist turning of the plug within the valve to quite a high degree. Occasionally, such resistance is overcome by providing some means of moving the plug axially within the plug-receiving cavity in such a manner that it at least partially disengages from the plug-seating surfaces within the valve body in order to permit turning of the plug within the valve body. Oftentimes, when excessive torque is applied to conventional lined valves, the friction between the plug and adjacent lining of the body can be sufficient to cause tearing or spalling of portions of the lining material.

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