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Why were explosive valves used on the helium pressurization systems? Are explosive valves also used on systems pressurized with Nitrogen?

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  • $\begingroup$ Related: Why did the S5.2/9D21 engine have pyrocharges? $\endgroup$ Commented Feb 20, 2021 at 23:14
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    $\begingroup$ @RussellBorogove thanks, though I'm not sure the conclusions there are applicable here. Prompt pressurization isn't really necessary, and the explosive valves caused problems with debris entering the helium flow, requiring additional filters. Must have been a good reason for it. Maybe the valve requirements to hold helium without leaking are special? $\endgroup$
    – Innovine
    Commented Feb 20, 2021 at 23:26
  • $\begingroup$ @RussellBorogove Hmm, Soyuz uses "Electro-Pneumatic Pressurization Valves" on its high pressure helium, but I think these valves are required to close again as Soyuz is designed for long idle times on orbit (docked), and I don't think helium refills are available (I may be mistaken). $\endgroup$
    – Innovine
    Commented Feb 20, 2021 at 23:34
  • $\begingroup$ "pyrotechnics are typically used when you want something irreversible to happen reliably." $\endgroup$ Commented Feb 22, 2021 at 2:03
  • $\begingroup$ @OrganicMarble but why? As mentioned, the explosive valves added debris to the helium. Sounds like that reliability comes with its own additional risks. Is an electric valve so much less reliable? There are several other electrically operated valves which are not explosive, and sealing off the high pressure helium seems to me to be desirable. $\endgroup$
    – Innovine
    Commented Feb 22, 2021 at 12:02

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