missing helium?

[rjack321]

Sure seems like the helium in the supply bottle isn't 100% to start with.

 

[SoFlaDiver954]

It was bought and sold by the dive shop as suit gas. The outlet fitting on inert gas tanks (n2, argon, helium) is identical. So the dive shop inadvertently used the wrong supply gas to the booster and put the argon in his breathing tanks

Sorry, i wasn't very clear in my question. "This case" would be referring to Lermontov's tanks, not those from PfcAJ's story. Lermontov already stated that his helium source tested to be over 99%. I suppose they could have also used the wrong bottle, but it is unclear if there was even argon available.

 

[wedivebc]

Just to amplify a couple of points mentioned above. My booster and associated hoses hold a significant amount of gas. If I had been boosting argon then switched to He without bleeding my lines and purging them it would throw off my calculations and still give me correct O2 readings.
The idea that gasses can separate or layer in tanks was ridiculous to my thinking when I first encountered blending errors and I would dismiss any idea that it was playing a role in my blending calculations but after experimentation with tank rolling in the shop where we rolled half the tanks and left the others stationary we found the test results of the rolled tanks to be closer to the expected mixes. My only explanation for that is that gasses at 200 bar behave more like a liquid than a gas at 1 ata.

 

[rjack321]

Sorry, i wasn't very clear in my question. "This case" would be referring to Lermontov's tanks, not those from PfcAJ's story. Lermontov already stated that his helium source tested to be over 99%. I suppose they could have also used the wrong bottle, but it is unclear if there was even argon available.

That would depend on the analyzer as helium is not analyzed directly.
Analyzers using a temperature cell are going to "see" if there's another inert in the supply bottle like argon. The divesoft analyzer is assuming you have trimix and if you have another foreign gas in there (not o2 or n2, at percent quantities) it won't read the helium correctly.

 

[lermontov]

i was assisting the blending so no argon involved - theres only a few options i can have a reasonable explanation
-the digital meter on the blending board is out of calibration or maybe the read out wasnt zeroed before adding new gas
-there was a gas loss when switching feeds or the helium went back into the supply tanks (unlikely with a non return valve)
-some gas compressing issues

annoyingly i had already dumped a 3l mix because the mix wasnt right so maybe it is the mixing gauge on the board -or just human error

 

[Jared0425]

Lermontov, in the past when I have filled tanks, it takes a few hours for the gas to settle correctly. It does seem that the gas will layer at first. Helium doesnt like to play nicely with other gases.

 

[stuartv]

good point but no -one cylinder was a 12 l and the other 3 litre

What does this mean? You filled 2 tanks the same way and both came out at TX17/20?

If not, which tank was wrong and what order did you fill the tanks? Or, they both started from empty and you filled them both at the same time using 2 different whips from the same compressor/booster?

 

[stuartv]

Just to amplify a couple of points mentioned above. My booster and associated hoses hold a significant amount of gas. If I had been boosting argon then switched to He without bleeding my lines and purging them it would throw off my calculations and still give me correct O2 readings.

This is what I was wondering about. I just recently got my Gas Blender card and started doing my own fills.

If I'm filling a 3L for my CCR, I would think that the amount of gas in the lines to/from the booster could hold enough volume to throw off the mix. In a 12L, not as much.

So, when I run the booster, I have been starting by opening the line from the source through the booster and then bleeding it from the end of the whip where the cylinder is connected before I open the valve for the cylinder I am filling. Especially if I don't know who was using the booster before me and what they were boosting. The shop where I'm doing my fills doesn't have argon that I know of, but still. I want my mixes to be as accurate as I can make them.