Improved butterfly valve

Abstract

A butterfly valve comprising a body 1, a passage 2 extending through the body, a closure or butterfly member 3 mounted in the passage 2 to pivot about an axis orthogonal to the axis of the passage so as to be movable between a closing position in which a sealing element fixed or formed on the periphery of the disc of the closure member has a sealing contact with a seat 8 carried by the body and a fully open position roughly perpendicular to the closing position, the peripheral surface of the closure member 3 and the conjugate surface of the seat 8 being conical surfaces defined by two cones of revolution, while the axis of rotation of the closing member is offset along the axis of the passage in a direction away from the apex of the cone defining the surface of the seat relative to the mean plane of the disc of the closing member, wherein for a given value of the apex angle 2.phi. of the cone C.sub.1 defining the seat of the valve and for a given position C of the axis of rotation of the butterfly member in an orthonormal system Ox,y,z of which one of the axes is coincident with the axis of said cone, there is defined a joint plane of the butterfly member with its seat of which a couple of points in respect of which the minimum angle of disengagement is maximum, has for trace a point Q located in the plane (Ox,z) of the system and of which the coordinates and the angle of disengagement are given by the following approximate relations: ##EQU1##