| 摘要 |
PURPOSE:To reliably close a main valve, by providing a timer for continuing a closed condition of the main valve for a predetermined period of time by an actuator after closing of the main valve. CONSTITUTION:It is detected by a closing operation of a limit switch 29a that a main valve 3 has been closed, and the closed condition of the main valve is indicated by lighting up a valve closing indicator lamp 30a provided at a control center or the like. After closing of the main valve, a solenoid 17a is excited for t seconds set by a timer 27 to continue the closed condition. Accordingly, even after closing of the main valve 3, a right cylinder chamber 18c is supplied with air from an air piping 10. As a result, a piston 18b is urged in a direction of an arrow X2 continuously after closing of the main valve to continue to drive an operation handle 3a of the main valve 3 in a valve opening direction. Thus, although an operational force of the operation handle 3a just before closing of the main valve is large, the main valve 3 is continuously closed for a predetermined period of time, thereby ensuring the closed condition. |
