Secondary backseat for gate valve

An expanding gate valve comprising:

• a valve body having a flow passage extending therethrough and a valve chamber intersected by the flow passage;
• a pair of valve seats, one valve seat surrounding each of the flow passages adjacent the intersection of the valve chamber;
• an expandable gate assembly element slideably mounted within the valve chamber for movement in a collapsed condition between open and closed positions relative to the flow passages, said gate assembly including a gate member and a segment which are expanded away from each other at the open and closed positions and are provided with ports which are aligned with one another and the flow passages in the open position, said gate member and segment being each provided with an outer sealing surface for sealing against said valve seats when the gate assembly is expanded in the open and closed positions;
• a bonnet assembly secured to said valve body having a central bore communicating with the valve chamber, the central bore having a longitudinal axis and a coaxial frusto-conical counterbore portion adjacent the valve chamber providing a bonnet backseat surface;
• a valve stem connected to said gate assembly element and extending coaxially through the central bore of said bonnet assembly, said valve stem being axially movable to move for said gate assembly between open and closed positions of the fluid flow passages of the gate valve;
• means for backseating said valve stem on the bonnet backseat surface in response to axial movement of said valve stem, said backseating means including a metal seal ring having a outer sealing surface, the metal seal ring being slideably mounted on said valve stem within the valve chamber, the slideable seal ring having a first axial position on said valve stem whereby initial contact is made between the seal ring and said bonnet backseat portion in response to axial movement of said valve stem, the slideable seal ring being movable to a second axial position on said valve stem in response to further axial movement of said valve stem to establish a metal-to-metal seal between said valve stem and said bonnet assembly;
• and
• means for repositioning the metal seal ring from the second axial position to the first axial position about said valve stem in response to opposite axial movement of said valve stem.

An improved gate valve of the type having a valve body with a flow passage extending therethrough and a valve chamber intersected by the flow passage;

• a valve closure element positioned in the valve chamber to control fluid flow through the gate valve;
• a bonnet assembly secured to the valve body and having a central bore communicating with the valve chamber;
• the central bore having a frusto-conical counterbore portion adjacent and facing the valve chamber;
• a valve stem connected to the valve closure element;
• wherein the improvement comprises:
• means for backseating said valve stem on the bonnet backseat surface in response to axial movement of said valve stem, said backseating means including a metal seal ring having a outer sealing surface the metal seal ring being slideably mounted on said valve stem within the valve chamber, the slideable seal ring having a first axial position on said valve stem whereby initial contact is made between the seal ring and said bonnet backseat portion in response to axial movement of said valve stem, the slideable seal ring being movable to a second axial position on said valve stem in response to further axial movement of said valve stem to establish a metal-to-metal seal between said valve stem and said bonnet assembly;
• and
• means for repositioning the metal seal ring from the second axial position to the first axial position about said valve stem in response to opposite axial movement of said valve stem.