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# Pressure, vacuums, and the on earth equivalent? Answered

One atm is equivalent to about 14.7 psi.  Does that mean that if one was in a perfect vacuum a vessel sporting 1 atm would need only hold the pressure of 14.7 psi?  It seems to me that in space (not a perfect vacuum) a craft would only need to hold maybe 12 psi (of course when messing with human life I would definitely allow for 150 to 200% tolerance, but in the end 24 psi still isn't very much is it.  Is there more to it than this, or are all those quotes about how hard it is to deal with a vacuum and how things must be super strong a little over blown.  Going just 11 meters under water exposes you to a little over double air pressure at sea level.  Someone in just a diving suit has been to over 60 times atmosphere and the deepest submarine dive I could find was 1083 atm at around 11000 m.  It just seems to make holding out a vacuum a little overrated.

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## 7 Replies

iceng (author)2014-10-23

It wouldn't make sense to over pressurize a space station that certainly has a over pressure release valve to avoid metal tearing where space suits operate around 9 PSI.

And 14 pounds per square inch does a pretty good job of collapsing a 55 gal drum on just a partial vacuum.

seedorfj (author)2014-11-11

I don't think I wanted to over pressurize anything... And I'm lost at the whole collapsing thing. Watch this https://www.youtube.com/watch?v=qjrR_SX4aBg its a 55 gallon drum holding 65 psi, string some of those together and you have a space station sleeping chamber [sarcasm].

iceng (author)2014-11-11

Fun vid...

steveastrouk (author)2014-10-23

For one thing, orbiting a pressure vessel is a lot harder than sinking one. Space is a hell of a lot more vacuum than -12PSI, like harder than the hardest vacuum on earth, and not too far from the earth either. IIRC Apollo spacecraft were only filled with oxygen and nitrogen at 60:40, and around 4.5 PSI, because holding a lot of pressure in a big box is actually HARD.

seedorfj (author)2014-11-11

You made a good point with the whole orbiting thing, but I'm not sure on your point about space being a harder vacuum. If zero atm is an absolute vacuum (impossible even in space). And at sea level pressure is 1 atm or 14.695 psi, I get the feeling holding out a vacuum with an internal pressure of 14 psi (although this pressure is far more than currently used in space) wouldn't be as impossible as it is made out to seem. Unless there is some cumulative effect of a vacuum and you don't need more than 6 psi, I think containment is one of the easiest obstacles to overcome.

Josehf Murchison (author)2014-10-23

It’s the cumulative effect, psi + psi +psi and so on for every square inch.

10 psi is nothing but over an aria of 4x8 feet that is 46,080 lb. pressure on a
structure.

It is how a car tire works the tire is only filled with 28 psi yet it holds up a 2,000
lb. car. Why? There are 4 tires; the bottoms of the tires are flat on the ground, that flat spot only needs to be roughly 18 square inches on each tire to hold the car up at 28 psi.

A scuba diver equalizes the pressure in his body to the pressure outside of his body that is why they get the bends if they come up to fast.

A submarine uses its shape and the thickness of steel on its pressure hull to withstand the pressure of the deep ocean. Works the same way you can’t crush a chicken egg when you press on the ends.

-14 psi or 0.7 psi collapses a 5 gallon pail because the total pressure on the outside of the pail is 50,668 lb.

Joe

seedorfj (author)2014-11-11

I'm aware of how pressure works, I used crushing as a high stress on earth example, and I wouldn't be suprised if tensile strength was more than compressive strength, don't take my word for it though. Who care about collapsing a 5 gallon bucket? First off, its not build for pressure (flat top, flat bottom), second, space isn't going to be crushing anything, its going to pull it appart, I would be curious to see how much pressure a 5 gallon bucket can hold.