Controlled floating seat for gate valves

Claim 1

In an expanding gate valve having a valve body providing a fluid flow passage therethrough, a valve chamber in the body communicating with the flow passage, and an expanding type gate assembly in the valve chamber movable in a collapsed condition between open and closed positions and disposed in an expanded condition when in the open and closed positions, the improvement comprising: an annular groove extending around the flow passage directly in said valve body, said groove opening to the valve chamber and having a bottom surface spaced from the valve chamber; an outer surface of said groove having a generally cylindrical portion spaced from the valve chamber and a frusto-conical portion adjoining said cylindrical portion, sad frusto-conical portion terminating adjacent the valve chamber and inclining inwardly toward the flow passage as it extends toward the valve chamber; an annular valve seat in said groove having a sealing surface facing the gate assembly for sealing contact therewith when the gate assembly is in its expanded condition, said valve seat having a base for contact with the bottom surface of the groove to limit movement of said seat away from the valve chamber; an outer side of said valve seat having a generally cylindrical surface adjacent said base and contacting the cylindrical portion of said groove, said cylindrical surface being of lesser width dimension in the direction of the axis of the flow passage than the width dimension of said cylindrical portion of the groove to permit movement of said seat in the groove toward and away from the valve chamber; and a frusto-conical surface on said outer side of the valve seat between said cylindrical surface and said sealing surface, said frusto-conical surface extending a distance of at least one-third the thickness of said seat between the sealing surface and base surface thereof, and having a cone angle of from about one degree to about ten degrees, said frusto-conical surface contacting the frusto-conical portion of said groove to limit movement of the valve seat toward the valve chamber such that the gate assembly is substantially clear of said sealing surface of the valve seat when in the collapsed condition, said valve seat being metallic and having a shrink fit within said groove.