Patent ID: 7775505

Claim:
A butterfly valve comprising a seat ring fitted to the inner peripheral surface of a hollow cylindrical valve body, a stem supported on the valve body via through holes of the seat ring and a discal valve disc supported with the stem mounted in a valve shaft hole of the valve disc, wherein the valve disc is opened/closed by being rotated with the rotation of the stem, wherein an annular protrusion having a first tapered surface with the outer periphery inclined from the direction of the valve axis is formed radially inward on the peripheral edge of each of the through holes on the inner periphery of the seat ring, the first tapered surface being inclined at an angle in the range of 20° to 40° with respect to a plane perpendicular to an axis of the stem, and wherein a bowl-shaped annular depression having a second tapered surface engaged with the first tapered surface is formed on the inner periphery of each opening end of the valve shaft hole of the valve disc, the second tapered surface being inclined at an angle in the range of 25° to 45° with respect to the plane perpendicular to the axis of the stem, the angle of the second tapered surface being larger than the angle of the first tapered surface.