Weight of air?

Discussion in 'Tanks, Valves and Bands' started by Divin'Hoosier, Oct 27, 2006.

  1. Divin'Hoosier

    Divin'Hoosier Divemaster

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    All of the tank specs tell you how much a tank weighs when empty. After looking around, I haven't been able to find the formula to use to approximate how much a full tank weights. How much does compressed air weigh? Is there a common value per cf of compressed air? Does it differ by max pressure (2640 v. 3000 v. 3442)?
     
  2. victor

    victor Loggerhead Turtle

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    1 cubic foot of air weighs 0.0807 lbs at standard preasure and temperature
    there is approx 80 cubic feet of air in a normal rental tank at 2400 psi
    so the air in the tank weighs approximatly 6.4 lbs
    If you enter at 2400 and exit at 500 then you will be about 5.1 lbs lighter than when you went in.
     
  3. SparticleBrane

    SparticleBrane Surface Interval Member

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    ^ Most rental tanks here in the US are Al80s, thus they have 77.4cf at 3,000psi, not 2400. ;)
     
  4. victor

    victor Loggerhead Turtle

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    Sorry more used to BAR
    Weight of air 77.4 cubic feet = 6.25 lbs
    Swing between 3000 psa and 500 psi = 5.2 lbs
     
  5. xiSkiGuy

    xiSkiGuy Single Diver

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    You can roughly say that every 13cf of air weighs one pound. So a E8-130 has 10lbs of air in it when full.
     
  6. donacheson

    donacheson Manta Ray

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    Each 13 cubic feet of air (at 1 atmosphere and normal temperature) weighs about 1 pound. Hence, an aluminum 80 holds about 80/13 = 6 pounds of air. For the metric folks, an 11 liter tank filled to 200 bar holds about 2200 liters of air (at 1 atmosphere and normal temperature), which weighs about 2.6 kilograms, or roughly 1.2 kilogram per 1000 liters.
     
  7. padiscubapro

    padiscubapro Tech Diver

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    also remember a tank filled with nitrox or trimix will have a different weight than air.. Nitrox is not significantly different but a high He mix will be considerably lighter..

    see this thread at rbworld
    http://www.rebreatherworld.com/decompression-gas-choices/813-how-much-does-gas-weigh.html?highlight=weight+GAS#post7356
     
  8. jeckyll

    jeckyll Loggerhead Turtle

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    http://www.techdivinglimited.com/pub/tanks.html

    That should give you a fair bit of data :)
     
  9. donacheson

    donacheson Manta Ray

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    True, but probably well beyond the scope of the info Divin' Hoosier needs. <G>
     
  10. Divin'Hoosier

    Divin'Hoosier Divemaster

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    Great info. Thanks. Everyone has provided me the info that I need, and then some. Thanks again.
     
  11. JAMIE MCG

    JAMIE MCG Nassau Grouper

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    Myth Busters had an episode where they informed if you put a cylinder around the Eiffel Tower the air inside the cylinder would weight more than the iron,( material ), that floored me.
     
  12. Divin'Hoosier

    Divin'Hoosier Divemaster

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    Not quite sure I understand. So if the space under the Eiffel Tower were somehow made into a compressed air cylinder, the weight of the air would weight more than the steel in the cylinder, or the steel in the Eiffel Tower? Please explain more. I'm just curious.
     
  13. SparticleBrane

    SparticleBrane Surface Interval Member

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    I disagree with MythBusters.

    Specifically...
    The Eiffel Tower (including the spire) is 1,052ft tall and at it's widest point, 423ft wide.
    Assuming a perfect cylinder (pi*[radius^2]*height), that's (pi)((423/2)^2) = 140,530.5 sq. ft. as the base, times 1,052ft for the height = 147,838,094.4cf inside the cylinder
    At 0.08lbs/cf that's 11,827,047.55lbs of air. The metal in the tower weighs 7300 tons; if you include everything it's 10,100 tons. That's 14,600,000lb or 20,200,000lbs depending on if you want to include just the metal or the entire structure.
     
  14. JAMIE MCG

    JAMIE MCG Nassau Grouper

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    Don't believe everything you see on T.V.

    Thanks SparticleBrane for working out the equation, and I'll stop spreading this lie, still they were only a few million pounds off still mind bottling when you think about air being that heavy:confused:
     
  15. SparticleBrane

    SparticleBrane Surface Interval Member

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    Definitely...the stuff is significantly heavy!
    A set of double 130s, between 0psi and full, is a difference of almost 21lbs.
     
    KWS likes this.
  16. The Kraken

    The Kraken He Who Glows in the Dark Waters (ADVISOR) ScubaBoard Supporter

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    Ya know, every now and then, and so rarely, a thread comes along that is just absolutely delightful . . .

    and this is one of them.

    Thanx . . .

    the K
     
  17. WarmWaterDiver

    WarmWaterDiver Photographer

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    If you raised the air pressure in the cylinder encapsulating the tower to 11.8 PSIG (the equivalent of 28 fsw depth) the compressed air would equal the weight of the entire structure given the figures above.

    If you raised the pressure to 4.3 PSIG (about 10 fsw depth equivalent) it would equal the weight of the steel given the figures above.

    Mythbusters just needed to top off the tank a bit . . .

    I'm using 60 degrees Farenheit air temperature
     
  18. 1982shawn

    1982shawn Nassau Grouper

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    You forgot to pressurize the tank.
    (Empty Volume/14.7psia)(max psi)= compressed volume
    (147,838,094.4/14.7)(2400)"well say its an LP tank"
    (10057013)(2400)=24136831738 cft of compressed air in the giant scuba tank
    (24,136,831,738)(0.08)=1,930,946,539lbs of air, almost 2 billion pound of air!
     
  19. Steve_C

    Steve_C Divemaster

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    Except of course the tower is very much not a cylinder so its volume is much less than the volume of a cylinder of the same height.
    Probably come closer with a cone but even that over estimates since the sides are very much concave. So tbones calculation shows even if you widely over estimate the volume but fix the amount of steel myth busters is still way off.
     
  20. halocline

    halocline Orca

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    I guess its a slow sports day today.
     

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