{{Short description|Valve used in marine steam turbine propulsion plants}} A '''guardian valve''' is a [[valve]] used in [[Marine (ocean)|marine]] [[steam turbine]] propulsion plants to prevent steam from leaking into the [[astern]] turbine while the vessel is operating in the ahead mode. It is normally installed between the astern [[throttle valve]] and the astern elements of the low pressure (LP) turbine. Typically only the LP turbine of a steam ship's propulsion plant has reversing blade elements. Steam leaking in such a manner would result in a loss of efficiency and possibly overheat and damage the turbine blades.<ref>{{cite web|title=T.S. Patriot State Engineering Manual|url=http://weh.maritime.edu/campus/tsps/manual/mainSteam.html}}</ref>
The guardian valve must be opened prior to any [[:wikt:maneuver|maneuvering]] situation, in order to permit the astern turbine to be used to bring the vessel to a rapid stop or to back down.
Any similar arrangement of a stop valve used to protect leaking past a throttling valve could also be referred to as a guardian valve.
==References== {{Reflist}}
[[Category:Safety valves]] [[Category:Marine steam engines]] [[Category:Steam turbines]]
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