| 摘要 |
PROBLEM TO BE SOLVED: To provide a valve element of a butterfly valve which can improve sealing performance at the time of full closing and decrease fluid resistance of flow passing through a comb-teeth-shaped protrusion part at the time of full opening, and a machining method which can obtain easiness and accuracy in machining the valve element. SOLUTION: A plurality of comb-teeth-shaped protrusions 17 of smooth outline are formed by a plurality of lines of circular shape in the vicinity of the peripheral edge part of a back face in the opening valve operating direction of the valve element 10 of a central-shaped butterfly valve supported through a valve stem in a body consisting of a rigid material. The front surface in the opening valve operating direction is formed to be almost a semicircular convex spherical surface 18, a plurality of straightening grooves 20 is formed at the peripheral surface of a valve stem insertion boss part 19 with its diametrical direction continuing in the orthogonal direction to the valve stem, and at the time of full closing, a valve element outer peripheral edge 11 and the inner surface of a sheet ring brought into tense contact with the inner surface of the body are formed to come into contact with each other at an inclination angle of 10 deg.±2 deg.. The valve element 10 is formed into a symmetrical shape with regard to the center of the valve stem insertion boss part 19, therefore, the flowing orientation of fluid is not defined.
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