Valve seat and method

摘要

Apparatus and methods are disclosed for a valve seat wherein the geometry of the seat is such that the resultant axial forces due to the differential between internal and external pressure across the valve seat result in a resultant axial force that urges the valve seat into sealing engagement with the plug or other type of closure member, regardless of the direction of the differential pressure. Thus the valve seat is urged against the closure member regardless of whether the line pressure or bonnet pressure is higher. In the same manner, a resultant axial force urges a seal seat of the preferred embodiment into sealing engagement with the valve body. An axially moveable seal bearing ring is positioned between the valve seat and the seal seat that alters the effective geometry of the seat elements when it moves between a first position and a second position. The seal bearing ring moves responsively to the direction of the differential pressure across the seat elements. In the present configuration, when valve flow path pressure is greater than bonnet pressure, then seal bearing ring is urged against valve seat and effectively becomes part of the geometry of the valve seat. When bonnet pressure is greater than valve flow path pressure, then seal bearing ring is urged against seal seat and effectively becomes part of the geometry of the seal seat. The valve therefore effects a primary and secondary seal when the valve is closed so that even if the primary seal leaks, then the valve maintains its seal because the reversed differential across the secondary or downstream seat assembly causes the valve to maintain a gas tight seal.