A valve with a plug with an outer surface of a resilient, low-friction material. The plug has circumferential bearing and sealing surfaces around the top and bottom thereof on the nominal plug taper, Plug Valves and on each side intermediate its flow ports, a pair of spaced, narrow sealing strips also on the nominal conical surface of the plug extending between, and merging with,Check Valves the circumferential bearing surfaces. When the plug is in closed position, the sealing strips and surfaces seal around the top and bottom of the plug and body, and on opposite sides of the body port.GATE VALVES In accordance with a preferred embodiment of this invention, the valve body has a tapered body cavity and the plug is cast with a nominal complementary taper. That is, as formed, the nominal taper of the plug core is constituted by circumferential sealing and bearing surfaces around its top and bottom, and four narrow sealing strips, one on each side of each plug flow port, extending from top to bottom to merge with the bearing surfaces. The circumferential sealing surfaces and the upright sealing strips are on a common frustoconical surface. Intermediate these sealing and bearing surfaces and sloping gradually into them, there are large recessed areas so that when the plug is encapsulated and placed under a small axial load in the valve body, firm sealing engagement with the body cavity wall is initially confined to surfaces of the Teflon overlying the frustoconical seal support surfaces. Because of the very gradually sloping transitional surfaces merging the common frustoconical sealing surfaces into the large recessed areas, an increase in the axial load will extend the sealing engagement with the body cavity wall to include circumferential portions of the recessed areas. This controls the area of frictional engagement to be at a minimum, and the recesses provide substantial accommodation for expansion and/or distortion of the Teflon. Preferably, the narrow upright strips are formed immediately adjacent the edges of the plug flow ports so that they are at the extremities of the imperforate flow blocking surfaces between the ports. Hence, when the valve is closed, sealing contacts are initially remote from the body flow port openings, and any distortion or cold flowing of the encapsulating material caused by such sealing contact, even over circumferentially displaced portions of the plug, will not cause the material to invade the flow ports. Because the plug is completely encapsulated, with the covering extending through the flow port as well, there are no edges exposed to the fluid stream. Hence, the covering can be relatively thin.

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