Valve seat assembly

In a through conduit gate valve structure having a valve body defining a valve chamber and inlet and outlet flow passages communicating with the valve chamber, a gate valve member having a port therein mounted within the valve chamber for reciprocal movement between open and closed positions relative to said flow passages, and an annular body pocket at the juncture of each flow passage with the valve chamber with each pocket defining a rear annular shoulder and an outer peripheral surface at right angles to said rear shoulder;

• an improved seat assembly mounted in each of said body pockets to provide upstream and downstream seat assemblies;
• each improved seat assembly comprising:
• an outer generally L-shaped seat retaining ring positioned within an associated body pocket in opposed contacting relation to said rear annular shoulder and outer peripheral surface of said body pocket;
• said L-shaped retaining ring having an annular shoulder and outer peripheral surface to form a seat pocket therein;
• an inner floating seat ring fitting within the seat pocket of said L-shaped outer retaining ring adjacent said annular shoulder and outer peripheral surface thereof, said outer L-shaped seat retaining ring and said inner floating seat ring having annular inner peripheral surfaces of the same diameter as said flow passages and forming a smooth continuation thereof;
• said L-shaped retaining ring having a rear face positioned in metal-to-metal contact relation with said annular shoulder of said body pocket and an annular groove in said rear face;
• a first O-ring received in said annular groove and maintaining sealing relation between said rear face and said annular shoulder of said body pocket under all conditions of operation of said gate valve structure and blocking fluid flow between the body pocket and retaining ring;
• said inner floating seat ring being of a generally rectangular cross-section having a front face engaging the gate valve member in sealing relation, a rear face adjacent the annular shoulder of the seat pocket of said L-shaped retaining ring, and an outer peripheral surface with an annular groove therein;
• a second O-ring received within the annular groove of said floating seat ring for sealing between the outer peripheral surface of said seat ring and said outer peripheral surface of the seat pocket of said seat retaining ring;
• said floating seat ring upon fluid pressure in the adjacent flow passage exceeding the body chamber fluid pressure a predetermined amount moving in a direction toward the gate valve member relative to said L-shaped seat retaining ring for maintaining a tight sealing relation with said gate valve member, said floating seat ring upon fluid pressure in said valve body chamber exceeding the adjacent flow passage pressure a predetermined amount moving out of sealing contact with said gate valve member to permit leakage of fluid from the body chamber into the adjacent flow passage;
• the maximum axial spacing between said floating seat ring and said retaining ring being less than the expanded diameter of said first O-ring between the opposed shoulders of said retaining ring and said body pocket thereby to maintain sealing relation between said retaining ring and said body pocket under all conditions of operation for blocking flow of lading from the adjacent flow passage to the outer peripheral surface of said body pocket and the outer peripheral surface of said seat retaining ring.