| 摘要 |
PROBLEM TO BE SOLVED: To facilitate making a check on damage or wear in seat structure of a butterfly valve. SOLUTION: This butterfly valve has a valve element seat 5 disposed at a peripheral portion of a valve element 4 and a valve casing seat 6 disposed on an inner circumferential face of a valve casing 1 which ensures sealability. A seat portion 9 of the valve casing seat 6 is formed in multi-layered structure, in which each surface of layers has a different marker, that is, a green face 11a, a red face 12a, and a brown face 13a herein. By the marker, the exposed layer can be discriminated from the layers, and degree of damage or wear can be detected.
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