Re: Helium in a tank?

Mark Conner N9XTN

I think helium from virtually any industrial gas supplier, even if labeled "balloon grade", is at least 99% purity, and often balloon grade is 99.99%.  Five nines is decent for most all industrial uses and six nines is towards laboratory grade.  You can ask if you got balloon grade or industrial grade, might even say on the invoice.  At Matheson (fka Linweld here), they put stickers on the balloon grade cylinders and the industrial grade ones aren't marked, but it's been several years since I got helium from them.

The small party balloon cylinders don't seem to have a fixed purity standard.  I read once that they sometimes blend with ~20% oxygen so that people who want to make Donald Duck voices with it don't end up asphyxiating themselves.  Don't bet your life on that though.

It's possible temperature effects might have affected your positive lift.  Other errors in the overall system probably are larger than the effect of having two vs five nines helium purity, unless you're doing flights where you measure lift in a few grams instead of a few pounds. 

73 de Mark N9XTN

On Sun, Jul 19, 2020 at 7:56 PM Larry <larry.phegley@...> wrote:
My payload went up at a slower rate that I had forecasted last time and I know I just got kind of lazy and sloppy.  But even with me adding weight to the payload and not accounting for it the helium should have caused the milk jug to go neutrally buoyant with the amount of gas that I got from the burst calculator.  We ended up emptying the bottle into the balloon which should have been 19 cu ft more than required.  I am guessing the burst calculator was correct.  Is there any reason for me to doubt the amount of helium in the tank as long as I verify the pressure is correct?  Should I ask the welding supply shop about the purity of their helium?

I am trying to be more careful this time


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