| 摘要 |
PROBLEM TO BE SOLVED: To reduce a load acting on an operating apparatus by narrowing a diameter of an opposite drive part of a valve stem comparing with a diameter of a driving part, in a butterfly valve wherein a valve stem is rotatably mounted on a valve casing boss by driving parts of both ends and the opposite drive part. SOLUTION: An upper valve stem 5 and a lower valve stem 6 are mounted on a valve element 2. The upper valve stem 5 forms a driving part connected to an operating apparatus, and the lower valve stem 6 forms an opposite drive part, and they are rotatably held by bushes 1, 11 in valve casing bosses 8, 9. The upper valve stem 5 and the lower valve stem 6 have prescribed diameters, the diameter of the lower valve stem 5 is formed narrower comparing with the diameter of the upper valve stem 6 subject to provide with bending allowable stress and twist allowable stress which are necessary for opening and closing operations of the valve element 2. When the valve element 2 is rotatably driven, a frictional resistance of the lower valve stem 6 in the valve casing boss 9 is reduced comparing with the frictional resistance of the upper valve stem 5 in the valve casing boss 8, a load applied on the operating apparatus is reduced comparing with a state where the diameters of the upper and lower valve stems 5, 6 are set to the same, and thereby, the valve element 2 is opened and closed with little torque.
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