Patent attributes
A butterfly valve includes a valve body with an internal flow passage extending in a direction of a flow passage axis, a disk-shaped valve member supported in the internal flow passage rotatably about a rotation axis perpendicular to the flow passage axis and having a spherical valve seat surface in an outer peripheral portion, an annular recessed portion surrounding the internal flow passage on the side surface of the valve body in a direction of the flow passage axis, and a seat ring attached to the annular recessed portion such that a valve seat portion provided in an inner peripheral edge portion thereof projects into the inner flow passage. The valve seat portion has a triangular cross section and is formed such that a bisector of a vertex angle in the triangular cross section of valve seat portion is perpendicular to a tangential line to the valve seat surface.
