GATE VALVE STRUCTURE

摘要

An improved valve seat structure for an expanding gate valve. The valve seat structure comprises a "floating" seat ring (60) which is loosely received in an annular seat pocket (52) surrounding the flow passage through the valve and is provided with an axial dimension which exceeds the depth of the seat pocket. The front seat face (61) of the seat ring is disposed adjacent the gate assembly (24, 26) and is provided with an annular groove (63) with an annular resilient sealing element (64) therein which protrudes beyond the face of the seat ring and forms a ring of sealing contact area encompassing the flow passage (14) when the gate assembly is expanded thereagainst. The rear face (66) of the seat ring (60) is also provided with an annular groove (63") and a second annular resilient sealing element (64") therein which protrudes beyond the rear of the seat ring. The two annular sealing elements are disposed coaxial and the inner diameter of the front sealing element (64) exceeds that of the rear sealing element (64") so that the front sealing element is therefore located a greater radial distance from the flow passage (14) than is the rear sealing element. Accordingly, when the gate assembly is expanded against the seat ring (60), the annular area of the front face of the seat ring which is exposed to flowline pressure exceeds the annular area of the rear face of the seat ring which is exposed to the flowline pressure whereby the seat ring is pressure energized towards the bottom (54) of the seat pocket (52). The annular resilient sealing elements (64, 64") and bottoms of the annular grooves (63, 63") are provided with cooperating wedging surfaces (80, 94 and 80", 94") which act to wedge the front face sealing element (64) towards the gate assembly and the rear sealing element (67) towards the bottom (54) of the seat pocket. The sealing elements increase the sealing ability of the valve seat in accordance with increasing flowline pressure and permit the valve seat structure to compensate for non-parallel conditions between the sealing surfaces of the gate assembly and valve seat and the valve body (12).