Abstract: A valve comprising a closure member including an annular peripheral sealing surface, a supporting shaft fixedly secured to opposing sides of the closure member, a housing including a cylindrical flow passage and means for rotatably supporting the closure member supporting shaft, means for rotating the closure member from a first position, whereat the flow passage is open, to a second position, whereat the flow passage is closed, an annular valve seat including an annular sealing surface, the housing further including an annular valve seat receiving channel selectively configured to support the annular valve seat for mating engagement with the closure member sealing surface when the closure member is at the closed position and the valve seat is at the neutral or zero pressure position, the valve seat including a recessed portion on one side thereof with a first annular groove extending axially into the valve seat from the recessed portion and a second annular groove extending axially into the other side of the

Abstract: A butterfly valve with a conventional resilient seal of rubber or plastic or the like is provided with a secondary seal of a hard, fire resistant material such as metal. The secondary seal is in the form of a split ring which is held in an expanded condition with a fusible link which will melt at some selected temperature such that the secondary seal is normally out of contact with the sealing surface of the butterfly. At the selected temperature, the fusible link melts permitting the secondary seal to contract into a sealing position to replace the resilient seal prior to or coincident with the destruction of the resilient seal by the high temperature.