Dual seat assembly for bidirectional gate valve sealing

A seat assembly for a gate valve, comprising:

• an inner seat having an annular sealing surface configured to engage a gate of the gate valve and a body sealing surface configured to seal against a valve body of the gate valve;
• an outer seat disposed radially outward of the inner seat and having an annular sealing surface configured to engage the gate and a body sealing surface configured to seal against the valve body;
• and
• a spring configured to bias the inner seat toward the gate;
• wherein the inner seat and the outer seat are captured within a body pocket of the gate valve and are configured to move independently of each other such that flow bore pressure acting on an annulus of the inner seat energizes the inner seat against the gate and the valve body when the seat assembly is on an upstream side of the gate, and force transferred through the gate from the upstream pressure area energizes the outer seat against the gate when the seat assembly is on a downstream side of the gate.

A method of sealing a gate valve, comprising:

• providing a gate valve having a valve body, a gate movable between an open position and a closed position, and a pair of seat assemblies disposed on opposite sides of the gate, each seat assembly including an inner seat configured to seal against the gate and the valve body, an outer seat disposed radially outward of the inner seat and configured to seal against the gate and the valve body, and a spring biasing the inner seat toward the gate;
• closing the gate to the closed position;
• applying pressure from an upstream side of the gate;
• energizing the inner seat of an upstream seat assembly against an upstream side of the gate and against the valve body by the spring and the applied pressure acting on an annulus of the inner seat;
• and
• energizing the outer seat of a downstream seat assembly against a downstream side of the gate by force transferred through the gate from the upstream pressure area acting on the inner seat of the upstream seat assembly.