Abstract

A butterfly valve comprises a valve housing (1) with an axial passage (4) for a fluid medium; a valve seat in the form of a seat ring (8) which is displaceable within a slot (7) in the valve housing in a radial direction relative to the axial passage, the seat ring elastically deformable as to its shape in the radial direction; and a throttle (5) arranged so as to be pivotable about an axis of rotation (23) between an open position and a shut-off position, the throttle having a seal face (21) on its periphery (18) which is pressed against the seat ring when the throttle is in the shut-off position. The shape of the seal face is defined by lines of intersection between the seal face and planes of intersection coinciding with a center line (22) of the throttle. Lines of intersection between the seal face and a first plane, coinciding with the axis of rotation of the throttle and perpendicular to a plane of symmetry of the throttle consist of circular arcs having a first radius, R, with a foot point on the axis of rotation. Lines of intersection between the seal face and all other planes of intersection have a curvature other than said first radius, R.