Abstract: The valve includes a closure disc (34) sealable at its rim to a valve seat (18) so that in this position the seat (18) and rim define between them an annular space (54) which is connected to a port (60) by passages (54, 56, 58) extending through a mating face (e.g. carbon fibre gasket (22)) of the valve seat (18). As shown the space (54) is a recess in the disc rim defined between fibre seal rings (46, 48) but other arrangements are disclosed in which the seal rings and/or recess may be accommodated in the valve seat. The port (60) may be used for leakage detection, pressure monitoring of bleeding or fluid injection.

Abstract: A butterfly valve has its seat formed on a detachable ring which is normal to the axis of the valve body. Both the seat and a co-operating seal on the valve disc have frusto-conical contact surfaces such that with the valve closed these surfaces are on a common cone with an axis inclined to body axis. The disc rotates about an axis offset beyond the larger ends of the contact surfaces and also offset to one side of both the body and cone axes. Operation of the valve and its maintenance are thereby improved.