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Thread: how much the compressed air weight?

  1. #1
    Inactive Member

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    Default how much the compressed air weight?

    for a 10L alu cylinder, charge from empty to 232bar, how much weight should gain?
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  2. #2
    Sharp Shooter

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    Buy a scale and perform a check... hehehehehe. But, seriously, I don't know the answer to that question, but whatever you do, DO NOT plot a graph and attempt to extrapolate for other volumes/pressures, because the relationship is non-linear as air is NOT a Newtonian gas.

    I think there are gas cylinder manufacturers' webpages that contain tables of such info I spotted some time ago. Do a Google.
    Hope you find an answer.
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  3. #3
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    also for other poeple stay in the inland, no dive shop avaiable.. how do u manage to get refill?
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  4. #4
    Marksman
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    there are 10 times as many dive shops in JHB compared to Cape Town
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  5. #5
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    [html] Thats funny, because there are fewer places to dive around here. I know about bass lake, wondergat and i think boesmansgat, but thats about it. Oh and your swimming pool when you're scraping algae off the bottom! [/html]
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  6. #6
    MOT: Thomson Pneumatic Rifles

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    To D!mn right, I had a choice of 4 dive shops within 8km in JHB and I now have the choice of 1 in about a 40km radius (OK so I am not living right in Durban)!!!
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  7. #7
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    I was told in smaller towns with no dive shops, they go to the fire department to refill tanks as the firemen need to keep a pump for the SCBA (no U) tanks anyway, not sure how true it is.........
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  8. #8
    Sharp Shooter
    Doctor BAM

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    boondock
    To get back to your question........, the fact that compressed air remains a gas there will be very little increase in weight, as opposed to LP gas, which becomes liquid and can therefore be weighed when you purchase it..... What is important is the remaining pressure in the SCUBA tank, which will give you an indication of how many times you can still use it..... Provided this pressure is still above your "sweet spot" fill pressure, you can keep on firing away....!!!!! It still remains the cheapest (and most constant) form of propulsion and that is why even Paintball went the same way with their new HPA setup. Someone must now spend time to also bring out a pony bottle to attach to the PCP to deliver constant air pressure to the reservoir with a pipe rigging.
    At ~R1.00 per charge, my BAM B-50 will do 80 shots at 12ft.pound easily.....!!! Compare that to CO2 use, and you will see the difference....

    Malan :claphead :claphead :claphead
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  9. #9
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    The weight difference is most noticable on a alu cylinder as opposed to an steel. Try diving on an ali at 10m & get down to less than 100bar & you start a rather swift ascent due to the weight change - this has happened to me more than once. On a 10L steel you don't notice it as the weight difference between empty & full is around 0.5kgs. Will try to find my compressor operator manual & see if that gives any exacts to weights.
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  10. #10
    Sharp Shooter

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    Not enough for it to need wheels....
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  11. #11
    Sharp Shooter
    Doctor BAM

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    Warlocke
    My reckoning is that the weight difference will be the same whether you use steel or aluminium Scuba tanks, so your estimation of 0.5 kg will be spot-on in all cases......, the difference in weight of the steel or alu. does not affect it, this is all accounted for in your ballast weights....

    Malan :blah :blah :blah :bowdown
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  12. #12
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    The difference between steel and aluminium will be the same, but you'll have almost 3kg air extra in the tanks.
    Still working my sums.
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  13. #13
    Marksman
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    aluminum tanks get more buoyant as they get empty...very noticeable near the surface...I only dive with steel tanks.

    Boondock was asking about the weight of the air in the tanks...
    A 10L tank at 200 bar holds 2000 liters of air which weigh about 2.5kgs..
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  14. #14
    Sharp Shooter

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    I figure that at 232bar into a volume of 10L at 20degC you'll get approx 2.3kg of compressed air.
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  15. #15
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    Ok Guys, Iíve decided to put my efforts into more constractive work instead of reflecting the negative.

    About the extra weight of a scuba tank of whatever they are made of such as aluminium or steel, the extra weight will be the same when pressurised. The only things that will differ are the pressures and the volumes of the scuba tanks.

    If you fill up a 10 litre tank to 230 bar, youíll have an increase of weight of 2.7 kg.
    If you fill a 10 litre to 300 bar, youíll have a weight increase of 3.5 kg.
    That is the weight of ďAirĒ that you put into the scuba tank at the pressures.
    It took me some time to get my equations together, but now that Iíve got it right, Iíll be able to give it to you within a second.
    Because itís an enclosed tank, it wonít make a difference to your altitude, sea level or up in the clouds where Iím am.
    Kind Regards
    Swannie
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