Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Lowest possible pressure (greatest vacuum)

  1. May 11, 2005 #1
    Out of curiousity..how big can vacuums get? as in..how low can the pressure be?
  2. jcsd
  3. May 12, 2005 #2
    Well, I suppose a vaccuums pressure is 0. Are you talking about a specific application?
  4. May 12, 2005 #3
    well i am indeed interested in how vacuums work. i've come up with an application of sorts with air quickly moving through a tube, (but it starts big gets small) so it creats a vacuum in order to get those speeds...now im wondering how much (or how great the vacuum would have to be) to basically make the pipe implode (thinkin stainless steel here...but probably will need something stronger). and also how would the moving air exit the tube if its a vacuum inside? wouldn't it just keep it pulled in?
  5. May 12, 2005 #4
    I believe the highest vacuum was measured in a space shuttle mission in the wake of a "shield".

    THE BEST ARTIFICIAL VACUUM ever achieved is produced behind a 4-meter disk dragged through Earth orbit by the Space Shuttle. Called the Wake Shield, the deflector pushes atoms out of the way, producing a small region in which the typical distance between residual atoms is a millimeter. Judging tenuousness by this some convention, the best pumped vacuum on Earth attains a residual atom spacing ten times worse---a tenth of a mm. By comparison, the atoms between stars are spaced a centimeter apart; in the gaseous halo of our galaxy the spacing is about 10 cm; and for intergalactic voids, it's up to 10 m, the lowest density (or highest vacuum) ever measured. (New Scientist, 25 April.)
    http://newton.ex.ac.uk/aip/physnews.369.html [Broken]​
    Last edited by a moderator: May 2, 2017
  6. May 12, 2005 #5


    User Avatar
    Science Advisor

    We have a large vacuum facility for the flow testing of nozzles and burners and I will tell you, when you are discussing the practicality of pulling a vacuum, the problems are exponential once you get past about 3-4 psia (in my experience). You have to be extremely careful of basic things such as pipe connections (flanges, fittings, etc...) that can create a leak. The quality of your pumps also come into play.

    You'll have to think of your system like a pump pumping air. The only differerence is that instead of your tube receiving the output of the pump, it is providing the source. Therefore, you will be on the low side of the pump and thus the lower pressure. You will have to have flow through the system (system being everything including your pipe).
  7. May 12, 2005 #6


    User Avatar
    Science Advisor

    infamous - vacum is a relative thing, in relation to the vacum of space it is easy to say that air is just under 15 psi and varies based on altitude, temperature, and humidity. Its also the pressure that will support a column of mercury 760mm (29.92 inches) tall and you could look at pascals and so on, but its irrelevant to your real question.

    To crush the tube you would need to have a tube weak enough to collapse with the 15psi external load. If you can't simulate that with air pressure, you could construct a simple water tank to exert the pressure on the tube to see if it would fail. Its doubtful, they use rubber hoses to carry vacums up to 27-28 inches of mercury without them collapsing.
  8. May 12, 2005 #7
    A fun experiment. Take a 45 gallon drum, metal is preferred. Fill it to about a third or half with water. Boil off the water and while it is still steaming, put the cap back on, tightly. Step back, a little farther, just a smidgen more, there that should do it. Hit it with a stream of cold water. Oh and plug your ears, it can be a bit loud.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook