| 摘要 |
A valve actuator having a cylinder and a piston is connected to a gas generating device for closing the valve in an emergency. A gas generating powder charge in the device is ignited by a firing pin or a hot filament released or energized by a circuit including a switch which closes in response to a given condition, such as an abnormal fluid pressure or rate of flow through the valve, whereupon the generated gas moves the piston to close the valve.
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