Abstract: In a butterfly valve having: a seat ring that is mounted on the inner circumferential face of a valve body; a valve stem that passes through a through hole in the seat ring, and is supported by the valve body; and a discoid valve element that is supported by way of fixing the valve stem in a valve stem hole, and which is opened and closed as a result of the valve element turning together with the valve stem turning, a hollow cylindrical bush is inserted into the through hole in the seat ring, and is mounted in a sealed manner in a valve stem fitting hole provided in the valve element, without projecting beyond the outer circumferential face of the seat ring.

Abstract: A butterfly valve includes a seat ring fitted to an inner peripheral surface of a hollow cylindrical valve body, and a discal valve disc in which a shaft is mounted. The shaft is rotatably mounted in through-holes of the seat ring. An annular protrusion having a first tapered surface inclined at 20°-40° with respect to the valve axis is formed at the peripheral edge of each of the through holes of the seat ring. A bowl-shaped annular depression at each end of the valve shaft hole includes a second tapered surface inclined at 25°-45° with respect to the axis and engaged with a respective first tapered surface.

Abstract: A butterfly valve, in which fluid leakage inside a valve disc and from a shaft seal part between through holes of a seat ring and a stem is prevented, when the valve disc is displaced under fluid pressure with the valve closed. Without increasing the operation torque of the stem, the fluid leakage is prevented even after continuous on/off (open/close) operations over a long period of time. The butterfly valve includes the seat ring fitted to the inner peripheral surface of the hollow cylindrical valve body, the stem supported on the valve body via the through holes of the seat ring, and the discal valve disc with the stem mounted and supported in the valve shaft hole. The annular protrusion having the tapered surface with the outer periphery thereof inclined with respect to the valve axis is formed radially inward of the peripheral edge of the through holes on the inner periphery of the seat ring.

Abstract: A seat ring having a hollow cylindrical body portion with a flange surface as each of its side surfaces. The cylindrical body portion has stem through-holes above and below along a stem axial direction X and a stem penetrates said through-holes. An outer circumference of the body portion is formed in an elliptic shape with the stem axial direction X as its longitudial axis. The thickness of the body portion where the stem through-holes are provided is the maximum while the thickness of the body portion along an axis perpendicular to the longitudinal axis is the minimum.

Abstract: A seat ring having a hollow cylindrical body portion with a flange surface as each of its side surfaces. The cylindrical body portion has stem through-holes above and below along a stem axial direction X and a stem penetrates said through-holes. An outer circumference of the body portion is formed in an elliptic shape with the stem axial direction X as its longitudial axis. The thickness of the body portion where the stem through-holes are provided is the maximum while the thickness of the body portion along an axis perpendicular to the longitudinal axis is the minimum.