Abstract: A ball valve seat arrangement is provided that permits relief of cavity pressure. The arrangement includes a valve body for receiving a resilient annular seat. First passages in the seat provide communication between the valve cavity, and a space formed between the seat and the valve body. When the cavity pressure reaches a certain level, a sealing point between the seat and the valve body is lost. Communication is thereby provided between the space and the valve passage to achieve cavity pressure relief.

Abstract: A ball valve seat arrangement is provided that permits relief of cavity pressure. The arrangement includes a valve body for receiving a resilient annular seat. First passages in the seat provide communication between the valve cavity, and a space formed between the seat and the valve body. When the cavity pressure reaches a certain level, a sealing point between the seat and the valve body is lost. Communication is thereby provided between the space and the valve passage to achieve cavity pressure relief.

Abstract: A top open ball valve assembly which includes a pair of camming plates, one at the top and one at the bottom of the plug. The camming plates are oval and in their minor axis are clear of the floating valve seats. There are lost motion slots to allow the plug to travel between an open and closed position without moving the camming plates. In the event it is required to retract the valve seats, the plug is rotated more than 90.degree. so as to engage the camming plates to move them so that the major axis of the oval camming plates is aligned with the flow passage of the inlet and outlet ports, and the camming plates engage and retract the floating valve seats. Annular grooves are provided in the valve seat recess and in the valve seat whereby they are radially aligned when the valve seats are retracted, and an elongated coil spring can be inserted in the passage formed by the grooves to block the valve seats in their retracted position.