Butterfly valve

A butterfly valve comprising:

• a valve body formed therein with an internal flow passage extending in a direction of a flow passage axis;
• a seat ring attached to an inner peripheral surface of the internal flow passage;
• a valve stem supported by the valve body to be rotatable about a rotation axis;
• a substantially disk-shaped valve element connected to the valve stem to be rotatably supported by the valve body and being placed in the seat ring, said internal passage being closed and opened by rotating the valve element about the rotation axis to bring a peripheral edge portion of the valve element into and out of contact with an inner peripheral surface of the seat ring, wherein
• the valve element has an annular outer peripheral edge surface circumferentially extending thereon, and is formed, at opposite positions in the direction of the rotation axis on the outer peripheral edge surface, with two valve stem openings for allowing the valve stem to pass therethrough, said outer peripheral edge surface of the valve element further provided with two annular opening raised portions each protruding from the outer peripheral edge surface and extending along the periphery of the corresponding valve stem opening, and peripheral edge raised portions each protruding from the outer peripheral edge surface and extending in the circumferential direction of the valve element so as to connect between the two opening raised portions, each of said peripheral edge raised portions having a peripheral edge sealing surface that extends along a top thereof to be like an arc in the circumferential direction and flat in the width direction, and chamfered surfaces inclined at a predetermined angle relative to the peripheral edge sealing surface toward the outer peripheral edge surface of the valve element and extending along both sides of the peripheral edge sealing surface,
• the seat ring is provided with an outer peripheral surface, an inner peripheral surface, and an annular protrusion protruding from the outer peripheral surface and extending annularly, and the valve body is provided on the inner peripheral surface of the internal flow passage with an annular fitting groove for the annular protrusion of the seat ring to fit therein, and
• the seat ring is formed, at opposite positions in the direction of the rotation axis, with two through-holes extending from the outer peripheral surface to the inner peripheral surface to allow the valve stem to pass through the seat ring, the seat ring is formed, on the inner peripheral surface thereof, with two annular through-hole sealing surfaces each extending at the periphery of the corresponding through-hole to extend planarly, valve seat surfaces extending like an arc in the circumferential direction of the inner peripheral surface to connect between the two through-hole sealing surfaces, and inner peripheral transition surfaces connecting between the through-hole sealing surfaces and the valve seat surfaces, and the valve element is formed, on the outer peripheral surface, with annular opening sealing surfaces each extending on a top of the corresponding opening raised portion, and outer peripheral transition surfaces connecting between the opening sealing surfaces and the peripheral edge sealing surfaces, each of said inner peripheral transition surface extending like an arc to be coaxial with the through-hole and being located at a position to come in contact with the outer peripheral transition surface in closing the valve.