Gate valve structure

Claim 1

A gate valve structure for use in mains carrying fluid, said gate valve structure comprising: a valve casing having a through-bore for the flow of fluid, said through-bore having an inlet end and an outlet end, an elongated chamber intersecting said through-bore intermediate its ends and defining inlet and outlet ports in said through-bore to the chamber, a valve seat surrounding at least one of said ports in said through-bore, and a bore in the valve casing to the exterior thereof; a gate member having a chamber therein open to the exterior thereof by a bore, said gate member being slidable in the valve casing chamber from a closed position across said through-bore and seating against said valve seat to an opened position out of said through-bore; means for moving said gate member between said closed and opened positions, said means including interior threads operatively positioned within the bore of the gate member chamber and a non-rising valve stem extending through and out of the valve casing bore, said non-rising valve stem including an annular shoulder defining a thrust collar and operatively bearing upon the interior of said casing, retaining means on a portion of said valve stem extending outwardly of said valve casing, seal means between said valve casing and a portion of said valve stem within said valve casing bore, and exterior threads on said valve stem cooperating with the interior threads of said gate member; means to provide a seal between said valve stem and said gate member only when said gate member is in the fully opened position whereby the exterior threads on said valve stem are protected from fluid in the valve casing chamber, said last-mentioned means including an annular portion within the bore within said gate member outwardly of said interior threads and having a smooth cylindrical surface with a major diameter at least as great as a major diameter of said interior threads, said valve stem beneath said annular shoulder and above said exterior threads having a smooth cylindrical surface having a diameter no greater than the diameter of the cylindrical surface of the bore in said gate member, said cylindrical surface of said valve stem being arranged to telescope within the cylindrical surface of the bore in said gate member only when said gate member is in the fully opened position, an annular groove in one of said cylindrical surfaces and sealing means carried in said groove for sealing between said valve stem and said gate member only when said gate member is in the fully opened position.