| 摘要 |
PROBLEM TO BE SOLVED: To eliminate the malfunction of an excessive force acting on a part of a diaphragm, causing a crack in the diaphragm or gaining a tendency to bend, making a pipe line close imperfectly or fail to function properly at an emergency, while the pipe line is closed, in a conventional simultaneous opening valve. SOLUTION: Stepped portions 8a, the thickness of which is slightly larger than the depth of the rim of a lower valve 10, is provided inside a valve seat 8 into which the lower valve 10 of a main valve 19 pinching a diaphragm 6 and regulate the downward movement of the lower valve 10, whereby an unreasonable force is prevented from acting on the diaphragm 6, when the pipe line is closed with the bottom of the diaphragm 6 touching the top face of the valve seat 8.
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