| 摘要 |
PROBLEM TO BE SOLVED: To provide a metal seat butterfly valve capable of surely eliminating an occurrence of fluid leakage due to a drop of a surface pressure and a difficulty in opening a valve due to an excessive rise of the surface pressure even if a valve element is deformed by a fluid pressure exceeding a design value applied to the valve element when the valve element is fully closed. SOLUTION: Even if the valve element 1 is deformed when the fluid pressure P1 applied to the valve element exceeds the design value when the valve element 1 is fully closed, the elastic piece 51 of one valve casing seat 5A is elastically returned from the state shown by solid line to the state shown by a chain double-dashed line to press against a valve element seat 4A so as to act to avoid a dropping of a surface pressure against the one valve element seat 4A in order to surely prevent a fluid leakage from the valve element seat. Also, because the elastic piece 54 of the other valve casing seat 5B is slightly loosened by the elastic deformation from a state shown by the solid line to the state shown by a dashed line, the elastic piece 54 presses against the other valve element seat 4B to act to avoid the rise of a surface pressure with the other valve element seat 4B. Thus, a valve opening operation to rotate the valve element 1 in a valve opening direction can be facilitated.
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