Self compensating seat for a spherical plug valve

A ball valve, comprising:

• a. a valve body having inlet and outlet flow passageways and a valve chamber therebetween, a ball member having a passageway therethrough mounted in said valve chamber for rotation between open and closed positions of said ball member passageway relative to said inlet and outlet flow passageways;
• b. said valve chamber being located at the junctures of said flow passageways and having opposed end walls extending generally radially outwardly from said passageways;
• c. a one piece deformable annular metallic seal ring of a uniform generally rectangular cross-section positioned in said valve chamber around each of said inlet and outlet passageways to form upstream and downstream seal rings, said generally rectangular seal rings each having a relatively sharp inner edge portion in a substantially line sealing contact area with said ball member and in a spaced relation to the adjacent chamber end wall in a preloaded position, said seal rings each having an inner relatively large ball contact surface immediately adjacent the line contact area and out of contact with said ball member in preloaded position, each seal ring has an outer peripheral edge portion in sliding contact with the associated end wall such that said outer peripheral edge portion will slide on said associated end wall upon displacement of said ball member from one position to another as said ball member moves in general longitudinal alignment with said inlet and outlet flow passageways;
• d. the downstream seal ring upon positioning of said ball member in said closed position and displacement of said ball member downstream by fluid pressure to a pressure loaded position being pivoted generally about said outer peripheral edge portion with said outer peripheral edge portion sliding radially inward relative to the associated flow passageway and with the inner edge portion thereof being moved into contact with the adjacent chamber end wall and with said inner ball contact surface being moved into contact with said ball member to provide a relatively large contact area between the surface of said ball member and said downstream seal ring, said valve chamber end wall being spaced from said ball valve member a predetermined distance in said preloaded position such that displacement of said ball valve member from said preloaded position to said pressure loaded position will not deform said annular seal ring beyond a point which will prevent it from returning to its original free shape.