Floating seat structure for gate valves

Claim 1

A gate valve structure comprising a valve body having a valve chamber therein and inlet and outlet flow passages communicating with the valve chamber, an expanding valve assembly including a gate element and segment slidably mounted within the valve chamber for movement between open and closed positions of the valve assembly with said gate element and segment expanding away from each other at the fully closed position; said valve body having a counterbore about each flow passage adjacent the valve chamber to define an annular recess having a rear wall and an outer circumferential wall, said valve body having an end flange about each of the flow passages, each end flange havng an outwardly facing annular recess about the flow passage therein; a tubular insert fitting within the flow passage having cylindrical main body of a uniform cross section defining the flow passage and an annular flange about the outer end of said cylindrical main body fitting within the recess of the end flange, the inner end portion of said insert being positioned closely adjacent the gate assembly and having an outer peripheral surface defining with the rear and outer circumferential walls of the recess a pocket; and a metallic seat ring mounted within said pocket for floating back and forth movement relative to the gate assembly and the tubular insert and having a resilient face seal for engaging the gate assembly in sealing relation, said seat ring further having inner and outer peripheral surfaces with an annular groove about each of the peripheral surfaces, an O-ring being positioned in each of the grooves to seal between the peripheral surfaces and the adjacent surfaces forming the seat pocket.