(under subclass 455) Apparatus in which a valve opens in response to a change in internal fluid condition and will not return to its closed operative position on removal of the change in condition until a closing or resetting of the valve and/or a trip device is performed by an external operator, usually manually.
SEE OR SEARCH THIS CLASS, SUBCLASS:
62, for valve in which the valve is opened in response to a freeze condition and remains open until reset.
456+, for valves which close in response to condition change and require resetting, and see the search notes to subclass
