| 摘要 |
PROBLEM TO BE SOLVED: To reduce differential pressure generated in a starting period of opening a valve element, reduce operation torque, and immediately reduce abnormal pressure rise when generated in fluid flowing in a conduit. SOLUTION: This seat ring 12 of rubber type elastic material is provided with a cylindrical part 12a to cover an inner surface of a cylindrical valve body 11 of a butterfly valve, and a crown part 12b for a valve seat swollen on an inner surface of it. In the crown part 12b, plural communication holes 12c penetrating the crown part 12b in a width direction are provided, and the communication holes 12c are interlocked with opening and closing of the valve element 13 to be opened and closed.
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