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Old 26th December 2005 | 23:40
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gas-chamber
 
Joined: Oct 2005
Posts: 264
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From: in them thar hills
Maybe that's too general, and still requires you to know the power source in the 1st place, so maybe not practical in application. Usually, where the valve fails when power is lost is linked to the need for that system to be 'fail-safe'. Thus, anti-ice valves will often fail to the on position, pressurization ditto, so that when you suffer a major electrical loss you can at least continue in cloud and breathing normally. Others fail to off to conserve power. Sometimes the off position on the valve is the on position for the system - to both conserve power and fail safe the system. Others will fail in position selected - e.g. often the crossfeed does this, as you can work around it with selective use of boost pumps.
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