I am trying to understand the constraints on pressurant gas line sizes and lengths.

For a static volume, the lines can be small in diameter because there is no significant flow velocity and therefore no significant pressure drop along the line.

But when pressuring fuel tanks or other large volumes that change over time, the pressurant will need to support a substantial flow rate, and so there will be a pressure drop. The larger diameter of the line, the smaller the drop.

I would like to understand the relationship between length, diameter and pressure drop for gaseous helium when used as the pressurant, including any design considerations that may be important in rocketry and spaceflight scenarios.

I have been looking for some standards including in the NASA but so far I've found nothing.

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    $\begingroup$ I don't see how this could possibly be answerable. The safe flow velocity is going to depend entirely on the system it's being used in, it's not something fundamental to helium itself. $\endgroup$ Commented Apr 10, 2021 at 22:43
  • $\begingroup$ Welcome to Stack Exchange! I've adjusted the wording to better fit the site's style. Please feel free to edit further. $\endgroup$
    – uhoh
    Commented Apr 10, 2021 at 23:34
  • $\begingroup$ Constraint on length: the line needs to reach from where the He is stored to where it is used. $\endgroup$ Commented Apr 11, 2021 at 2:35
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    $\begingroup$ Seriously, I believe you've edited this out of any resemblance to the original. It asked about velocity, now that's not even mentioned in the question part of this post. $\endgroup$ Commented Apr 11, 2021 at 2:38
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    $\begingroup$ The edit also removes everything about the safety concerns and the use of helium. It's now just a basic question about pressure drop through a pipeline carrying a gas, something the original question didn't actually ask about at all, and something that seems more at home on engineering.stackexchange.com. $\endgroup$ Commented Apr 11, 2021 at 12:29


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