Dual backseat valve assembly

摘要

The present invention is directed to a dual backseat valve assembly comprising a valve body having an interior valve chamber and a generally horizontal flow passage; a valve gate adapted to reciprocate vertically within said valve chamber; a valve stem adapted to be received in threaded engagement with a gate lift nut mounted in said gate such that rotation of said stem causes vertical movement of said gate and a valve bonnet fixed to said valve body receiving said stem therethrough; wherein the valve stem comprises a radially extending portion defining a downward facing surface, a first enlarged diameter portion proximate the radially extending portion and a reduced diameter portion adjacent the first enlarged diameter portion; a first backseat seal comprising a radially energized seal ring fixed relative to said bonnet and having a first sealing portion for sealing against said bonnet and a second sealing portion which is adapted to be spaced apart from said reduced diameter portion when said valve is in normal operation and to engage said first enlarged diameter portion only when said stem is in a backseated position with said valve in the open position; a second backseat seal for providing a seal between said stem and said bonnet when said stem is in a backseated position with said valve in the closed position; and a structure fixed relative to said bonnet defining an upward facing surface adapted to engage said downward facing surface when said valve is in the open position to thereby tighten and lock said stem in the backseated position when said stem is moved against the fixed structure.