Valve structure having fluid pressure actuated seats

Claim 1

A valve comprising a valve body having upstream and downstream flow passages and a body space between said flow passages, a valve element in said body space mounted for movement between open and closed positions, annular downstream and upstream seat assemblies mounted in said valve body on opposed sides of the valve element, said seat assemblies being mounted for sliding movement toward and away from the valve element, a seal ring mounted on the face of each seat assembly adjacent the valve element and adapted to engage the valve element in sealing relation, recessed means on the valve body providing a sealed chamber on the back of each seat assembly, a conduit connecting the sealed chamber for the upstream seat assembly to the downstream flow passage only, and a separate conduit connecting the sealed chamber for the downstream seat assembly to the upstream flow passage only, said seal rings defining a perimeter of sealing contact with the valve element intermediate the inner and outer radial extents of said sealed chambers whereby fluid pressure from the upstream flow passage is in fluid communication with the sealed chamber of the downstream seat assembly to provide a greater force at the back of the downstream seat assembly than at the face thereof to bias the downstream seat assembly toward the valve element.