Butterfly valve

A butterfly valve comprising a body having an internal cylindrical bore with two radial coaxial passages diametrically opposed with respect to said bore, a butterfly including a spherical cap section and two coaxially projecting shafts rotatably mounted in said passages and providing pivotal movement of said butterfly in said body between opened and closed positions, an annular elastomeric seat of U-shaped section covering the bore and the outer side faces of said body, said seat receiving the shafts of the butterfly and including at each of said passages a portion of spherical shape substantially complementary to that of the cap section of the butterfly and a cuff portion surrounding the associated shaft, a support independent of the seat and constituted of an elastomeric material housed in an annular groove provided in said body which the support completely fills, said support having a free surface in contact with the base of the U-shaped section of the seat, said support comprising a cuff portion surrounding each said shaft and bearing against the cuff portion of the associated seat and permanently compressing the spherical portions of the seat against the respective cap portions of the butterfly to assume both sealing towards the exterior of the passages for the shafts and, in closed position of the butterfly, the continuity of the sealing, upstream and downstream, of the butterfly on the seat, said valve further comprising around each of said shafts, an annular element of triangular cross-section, a bearing for said shaft having a tapered face in contact with one of the faces of said annular element, a washer having a tapered face in contact with the other face of said annular element, spring means acting on said bearing to urge the same against said annular element, said body having a shoulder against which said washer bears under the action of said spring means transmitted through the annular element, said shoulder being at the level of the upper face of the cuff portion of the support, said cuff portion of said seat extending into sealing contact with said annular member to form a second seat thereat.