| 摘要 |
An installation control valve, for example for use in a fire fighting sprinkler installation, comprises a pivotal butterfly valve disc co-operable with a movable stop, which in one position abuts the valve disc to retain the valve closed against pressure forces acting thereon. A retaining mechanism is releasably held to resist stop movement and so prevent valve disc opening but is operable under a predetermined condition to permit stop movement from said one position to a second position. When the stop is in the second position, unequal pressure forces on either side of the valve disc cause same to move thereby opening the valve.
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