Butterfly valve

Claim 1

In a valve comprising an annular seat, a valve closure element cooperative with the seat and defining a peripheral annular groove which opens outwardly onto the periphery of the closure element and has an annular inner end face and a radially inner part and a radially outer part, and an elastomer sealing element having an annular head portion for contacting the seat in a valve-closing position of the closure element and a heel portion, the heel portion being disposed in said inner part of the groove; the improvement comprising in combination a first annular gap which is defined between said heel portion and said inner end face of the groove and extends throughout the width of said inner part of said groove, an intermediate portion connecting the head portion to the heel portion of the sealing element and defining a constricted portion in a free state of the sealing element before assembly of the sealing element with the valve closure element, two first confronting annular faces of said inner part of the groove which have a substantially rectilinear generatrix and are in gripping relation to the sealing element in a part of the sealing element consisting of the heel portion and excluding the intermediate portion whereby to prevent relative movement between the heel portion and the two first confronting faces but allow the head portion and intermediate portion freedom of movement and also allow the intermediate portion to be exposed to pressure of fluid controlled by the valve, the sealing element having in a free state and before assembly of the sealing element with the closure element a cross-sectional shape which is such that said head portion has, in a radially outer part of said head portion, a curvilinear convex contour which extends to a region of said head portion of maximum width and, in a radially inner part of said head portion, a contour defined by two contour lines which progressively converge in a direction toward said heel portion and terminate in said intermediate portion, said outer part of the groove being laterally defined by two second annular confronting faces which are radially inwardly divergent from each other and define with respective confronting faces surfaces of the interposed sealing element in a part of the sealing element consisting of the head portion and the intermediate portion a second annular gap on each side of the sealing element, each of said second gaps increasing in width in a direction radially inwardly from said region of maximum width of the head portion to said intermediate portion, a first annular surface substantially parallel to said seat in a valve-closing position of said closure element being connected to a radially inner end of one of said second confronting faces, said one second confronting face extending from said first annular surface at an acute angle, a second annular surface substantially parallel to said seat in a valve-closing position of said closure element being connected to a radially inner end of the other of said second confronting faces, said other second confronting face extending from said second annular surface at an angle of substantially 90°.