Hi everyone, I am working on an entrepreneurial project but I have very little scientific knowledge. (Once I receive venture start-up capital I will be able to employ a science and tech team!) I am working on innovative designs which use weather balloon technology, but I am struggling to calculate how much helium I can get from a specific tank for my applications. The canisters I am looking to purchase are 40 liters (which I assume refers to the compressed capacity - not the number of liters which flow out of the nozzle in decompressed form). According to the label - the canister pressure (at least that is what I think it is) reads 1,5 kg // 20 MPa @ 20 degrees Celsius The flow rate for my proof of concept testing is 15 liters of Helium (flowing - uncompressed Helium) per minute. At that flow rate, how long will a 40 liter tank last at the indicated pressure? I live overseas and my colleagues in the UK tell me that I need to purchase 14.9 cu ft (cubic feet) tanks which have 420 liters of Helium (which I assume means uncompressed Helium). If you do a search for "balloon time jumbo helium tank, you will see the exact size and type of canister I am looking for and it fills up to 50 9 inch latex balloons. However, when I do a search for Helium suppliers over here - some industrial suppliers have these massive 70 kg cylinders which are well over five feet tall and they only have around 50 liters of Helium per cylinder! Sorry if my question sounds silly, but am I missing something here? Perhaps some companies report on uncompressed liter for capacity and others report in the compressed liters? Can anyone assist?

The key is to understand what pressure these cylinders can hold. The figures you have been given (40L or 50L) tell you the volume of the tank. The amount of helium they can hold is determined by the pressure of the gas in the tank. You mention one figure for pressure: 20 MPa -- since one atmosphere pressure = 0.1 Mpa, this means that the tank can hold 200 atmospheres of pressure. If you fill the tank to this pressure it would hold an amount of He equal to 40L x 200 Atm = 8000L at 1 atmosphere. I am sure that no supplier would actually fill the tank to that pressure, so you need to find out out not only the volume of the cylinder but also what pressure of He they fill it to.