this post was submitted on 22 Dec 2023
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Why is a vacuum (holding a tube in compression and 10-14psi ) harder than pressure (holding the tube in tension at 200-1500 psi).
I used to work in a vacuum lab and one thing to consider is pumping efficiency drops as pressure drops. So everything leaks all the time right, and one strategy is to just pump harder.
However at low pressurers nothing is pushing the air into the pump for extraction, something like a bend can stop gas flowing around it dramatically where in high pressure the gas behind just pushes it through. So it gets more and more energetically demanding to keep pace with leaks.
Also pressuring a giant tube to multiple atmospheres also sounds like a nightmare. It's hard enough to keep pool toys inflated :p
It's not a total or high vacuum. It's a partial vacuum like -10psig.
Just to talk in international units to include everyone: I was under the impression it was supposed to operate at 1 mbar or 1/1000th of an atmosphere. That's into the transition between viscious and molecular flow iirc (for air at normal temps anyway). You're probably still pumping down with something like a scroll pump but it's not very efficient anymore.
Thinking about the number of opportunies for leaks. Every joint, every screw, every pump connection. How they all shift against each other as the sun warms and cools them, how you relieve the strain without introducing pourous materials. It's a fucking nightmare, and even if you manage all that you need to be pumping on it every few meters 24/7 to keep pressures that low with the realistic amount of leaks/in order to be able to pump down the local area where one occurs.
Like imagine if you needed a phat motor on every block to make roads work. The infrastructure demand is just unreal