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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.

uhoh
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Vulinhlanhla
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    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. – Christopher James Huff Apr 10 '21 at 22:43
  • Welcome to Stack Exchange! I've adjusted the wording to better fit the site's style. Please feel free to edit further. – uhoh Apr 10 '21 at 23:34
  • Constraint on length: the line needs to reach from where the He is stored to where it is used. – Organic Marble Apr 11 '21 at 02:35
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    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. – Organic Marble Apr 11 '21 at 02:38
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    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 https://engineering.stackexchange.com. – Christopher James Huff Apr 11 '21 at 12:29
  • @ChristopherJamesHuff no it doesn't and isn't "...including any design considerations that may be important in rocketry and spaceflight scenarios." The question asked "safely" not "safety" The question explains why it isn't safe to have a line that is too small in diameter; that could result in the pressure dropping too far when the velocity is too high. Remember that draining the tank is some kind of powerful pump, and that pump is an important player in the dynamics of the pressure in the tank. We shouldn't second-guessing the question rather than waiting to see what answers are posted. – uhoh Apr 12 '21 at 00:24
  • @ChristopherJamesHuff here also a question's scope is incorrectly represented. – uhoh Apr 12 '21 at 00:24
  • For pressure fed systems there is no "powerful pump". – Organic Marble Apr 12 '21 at 01:40
  • @OrganicMarble re "powerful pump" systems I'm guessing as a non-rocket-scientist that for at least kerosene there needs to be some gas line to make up the volume removed; positive pressure is important for structural integrity as well as working together with ullage to keep the fuel line to the powerful fuel pump filled with Kerosene. And for purely pressure-fed systems doesn't what happens with valves and with events in the combustion chamber present a dynamic (changing with time) load on the pressure of the fuel? Either way I think that this question about gas lines in rockets is answerable – uhoh Apr 12 '21 at 03:19

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