ok JD now I see what you want to do. You said that the guy sells helium by the pound; ask how many pounds go into the tank. The tank is then weighed after filling. You will need to determine the volume of the tank somehow, maybe by looking it up on internet and convert your weight to cubic feet.
Ultimately, the chart above should tell you how many baloons you can fill. Then maybe figure out how many baloons your blimp could hold. Volume = length x width x height for a cube. To find volume of a cylinder V = the number PI (3.14) x height. good luck
I just checked... the big welder type cylinders hold about 41 Liters, which translates to roughly up to 90 Lbs of liquid material.
I thought it could be a little more, since our 100Lbs LPG cylinders hold about 20 Gallons of liquid gas.
Anyway, as I stated, I find it to be in NO relation to the 1000 to 2000 pounds our local Helium guy says he can put into one of his party cylinders he rents for inflating balloons! This rationale is what started all my asking about HOW Helium is being sold.
So, I went and checked sellers in the US. And that's where I saw that MOST will sell Helium by the cubic footage it will inflate under normal circumstances. The same large "welder type" bottle then is marketed as a 290 cubic foot bottle! Obviously this can again NOT be the size of the bottle but the size of the expanded gas.
I know the sizes (fill volumes) of the airships I am looking at, so that would be a funny but OK way for me to estimate my gas needs and costs.
The issue at hand is, to know how much LIQUID gas I have to buy to inflate and at what rate per pound (liquid) or volume (liquid liters or Gallons) @ so-and-so many pesos.
Yet, the local Helium peddler with his 1000 to 2000 pounds of gas cramped into a 41 Liter bottle obviously does not help me much in finding what I am buying and how much I need. Hence mine wondering if there was some insider gas dealer's way to understand HIS rationale.
Yes, it's funny when a coworker of a company referred as potentially selling gas, is then referred to me as the one selling the gas... as a little biz on the side.... and then turns out to be the man behind the other gas and balloon outlet. But then, this is the DR.
J-D.