Dual seal ball valve

A ball valve having an upstream side and a downstream side, subject to upstream fluid pressure, from fluid passing through the valve from upstream to downstream, comprising:

• a. a valve body having a valve chamber therein and a pair of flow passages aligned at opposite sides of the valve chamber, each of said flow passages having an inner end facing the valve chamber and additionally having a recess around the inner end of each of the aligned flow passages;
• b. a generally spherically stopper member having an imperforate section and a section having a flow passage therethrough, the stopper member being mounted for rotation within the valve body, between a stopper position in which the valve is open and the flow passage of the stopper member aligns with the valve chamber flow passages and a stopper position in which the valve is closed and the imperforate section aligns with the valve chamber flow passages;
• c. a valve seat in the downstream recess around the inner end of the downstream flow passage, the valve seat comprising a ring shaped seat, having an inside portion aligned with the downstream flow passage and an outside portion and a sealing surface facing the stopper member and located between the inside portion and the outside portion, between which the stopper member rotates between the open and closed position such that the stopper member may form a primary, bubble tight seal with the ring shaped seat in response to upstream pressure acting on the stopper member when the stopper member is in the valve closed position, whereby the primary seal acts to seal the fluid under pressure from upstream fluid pressure from flowing past the primary seal when the primary seal is formed;
• d. a second downstream ring shaped seat member having an endface adjacent the stopper member slidably mounted around the outside portion of the downstream ring shaped seat, the second downstream ring shaped seat member having an interior facing recess facing the valve chamber therearound at the endface of the secondary ring shaped seat member adjacent the stopper member;
• e. an elastomeric seal member disposed in the inner recess of the secondary ring shaped seat member;
• f. a spring member having selected spring value to provide initial contact of the elastomeric seal member against the stopper member;
• g. responsive means responsive only to differential pressure caused by the upstream fluid pressure after the sealing surface of the ring shaped seat is in contact with the stopper member and if there is occurrence of leakage of the primary seal for providing sealing engagement force of said elastomeric seal member against said stopper to form a bubble tight, secondary seal;
• and
• h. the responsive means includes means to provide engagement force commensurate with the upstream line pressure, whereby the secondary seal acts to maintain a sealing engagement with the stopper member if the primary seal should leak.