Patent ID: 8002237

Claim:
A ball valve seat arrangement comprising: a valve body; and a resilient annular seat for sealing between the seat and a valve member, the valve member being at least partially spherical, the seat comprising: a valve member contacting portion for contacting the valve member; and a valve body contacting portion for contacting the valve body and forming a space therebetween and a sealing point therewith; the seat defining one or more first passages for providing communication between a valve cavity and the space; the seat defining one or more second passages which, but for the sealing point, would communicate the space with a valve passage to allow gas to vent from the space through the one or more second passages into the valve passage; the seat further comprising an inner peripheral portion, being disposed at an inner perimeter of the seat, and being distanced from an adjacent valve body surface defining a gap when the valve cavity is at a pressure less than a threshold pressure, and being movable, in the gap, towards the adjacent valve body surface upon the valve cavity reaching the threshold pressure, whereby sealing at the sealing point is lost thereby allowing gas to vent from the space through the one or more second passages into the valve passage to reduce the valve cavity pressure.