A plug valve has an actuating stem which is non-integral with the valve plug. The actuating stem is axially movable with respect to the valve plug to compressingly and sealingly engage an external sealing member in response to fluid pressure. The plug wedges itself into sealing engagement in response to fluid pressure.Balance Valves A plug valve comprising:
a valve housing having a flow passage therethrough; a valve plug rotatably fitted within said valve housing across the flow passage for controlling fluid flow in accordance to the plug's angular position relative to said housing; an actuating stem, Plug Valvessaid stem having at least two side portions, said stem having a shoulder, said shoulder extending radially outward from and separating said side portions, said stem being operatively connected to said plug, said stem being operatively fitted into a female recess in said plug, said stem being at least partially housed within said housing, GATE VALVESsaid stem having a greater clearance with said plug when said passageway is not in correspondence with said bore; said clearance providing for prevention of internal leakage past said plug when said plug is in the closed position; an external sealing member circumferentially disposed about the stem proximal to an axially adjacent section with respect to the shoulder on the opposite side thereof with respect to the valve plug; a first chamber at least partially defined by the end of the plug interacting with the stem, the valve housing and the side of the stem shoulder opposite the external sealing member; means for controlling the pressure of said fluid irrespective of the fluid pressure in said flow passage; means for permitting axial movement of the stem in response to fluid pressure in said first chamber to compressingly and sealingly interact the shoulder and the external sealing member. In accordance with the invention, a plug valve has a valve housing with a flow passage therethrough and a plug member rotatively fitted within the passage to control fluid flow through the passage in accordance to the plug's angular position with respect to the housing. A non-integral actuating stem operatively interacts with an end portion of the valve plug and axially extends therefrom in a direction transverse to the flow passage to rotate the plug relative to the valve body. The stem has at least three discrete sections including an intermediate shoulder section having a greater diametrical dimension than axially adjacent sections. An external sealing member is circumferentially disposed about a second axially adjacent to the shoulder on the opposite side of the shoulder with respect to the valve plug. The valve has a variable volume chamber at least partially defined by the end of the plug interacting with the stem, the valve housing and the axial side of the stem shoulder opposite the external sealing member. The invention includes means for permitting axial movement of the stem in response to fluid pressure in the chamber to compressingly and sealingly interact the shoulder and the packing member. Thus, the actuating stem moves transverse to the flow passage in a piston like manner to compressingly engage the external sealing member whenever fluid pressure is communicated to the chamber. In accordance with another aspect of the invention, a pressurized buffering media is applied to the valve internally of the external sealing member to constantly urge an anxially movable actuating stem into a sealing relationship with the external sealing member.

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