I have got self contained air breathing apparatus with pressure gauge and cylinder. Cylinder has marking that it's 6 ltrs. When I open valve pressure gauge shows me 250 bars. Can I calculate the overall volume of air by multiplying volume of cylinder by actual pressure? So in my case it would be 6 $\times$ 250 = 1500 ltrs. I've got nothing in manual, concerning this formulae, neither I heard about it. But it fits my experience pretty nice. Is it right to calculate like this? Thank you.

Well. I will explain, giving more details. I work with air cylinders and Breathing Apparatus for fire fighting. They are similar to those divers use. I have requirement, that all of the cylinders should be filled by not less than 1200 ltrs of air. But I have only pressure gauge. The problem is how can I be sure, that cylinder has 1200 ltrs. I need to convert somehow ltrs to bars. When I had 8ltrs cylinders, the pressure gauge had marking on 150 bars that it's enough. So I decided, that it would be 1200 ltrs. So I can calculate volume of air by multiplying pressure by gage and capacity (volume) of cylinder. I just wonder, may be it's just a coincidence and there is no such a formulae. That's why I ask to clarify me please. Am I right?

  • $\begingroup$ You mean the volume of the gas at standard pressure (i.e., 1 bar)? $\endgroup$
    – Kyle Kanos
    May 21 '17 at 11:30
  • $\begingroup$ Take a look please, I edited my post and added some details $\endgroup$
    – Valentina
    May 21 '17 at 16:50

Your calculation is correct : pressure in bars x canister volume gives you the approximate volume of the compressed gas at atmospheric pressure (which is approx. 1 bar). See typical instructions for diving canisters.

This is a simple application of the Ideal Gas Law $pV=nRT$. The pressures and volumes of a fixed amount $n$ of gas in two different states, but at the same temperature $T$, are related by
$pV=p_0 V_0$.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.