| 摘要 |
PURPOSE:To improve valve response by shortening a time period before the start of closing while maintaining a time period from the start to the end of closing at an optimum. CONSTITUTION:An on-off valve 9 is interposed in a first back pressure line 7 communicating a main vapor passage 2 of a valve box 1 and back of a valve body. The main vapor passage 2 of the valve box 1 and the back of the valve body is further communicated with a second back pressure line 18. Further, a second on-off valve 20 is interposed in the second back pressure line 18. A control unit 21 is equipped to detect forward travel of a valve body 4 and to close the second on-off valve 20. With this constitution, valve response can be improved.
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