Gas blending, stratification and very long dip tube. Any experiences?

[tbone1004]

Just monitor the temperature differential of the metal with your hand. A few degrees works, more differential works faster until the there is enough heat to warm the top of the cylinder. A 2"/50mm deep bath 110° F/43° C water (used for hot water suits) worked great in 50° F/10°C weather on K bottles.

I imagine a 60 watt incandescent light bulb near a set of doubles would be fine unless you are in a big hurry. Of course that is after the cylinders are cooled down from the filling process.

I use a stick, so when I put HE in, I just pulse the nitrox in behind it and have never had any issues with stratification.

 

[Chris H]

A long diptube will promote mixing. This particular example isn't dive related, but a dip tube was used for mixing. I worked in a specialty and welding gas fill plant lab. A customer wanted 6-packs of 50/50 Argon Helium, or 90/10. Regardless of the mix, the densities are very different. We couldn't roll the rack of 6 cylinders, so long dip tubes were installed. The cylinders with dip tubes analyzed, with correct results, in a shorter amount of time.

 

[Agro]

Heat sounds very good, I will try this, thank you!
I need O2 for rebreather, I need Trimix, I hardly ever need Nitrox. I use my O2 cylinders down to about 20 to 30 bar, booster makes 200 bar out of it. -Then I top the 20 bar O2 with air to desired Nitrox. This premixed Nitrox goes into compressor and diving cylinder. So no need for a nitrox stick.

 

[rjack321]

Heat sounds very good, I will try this, thank you!
I need O2 for rebreather, I need Trimix, I hardly ever need Nitrox. I use my O2 cylinders down to about 20 to 30 bar, booster makes 200 bar out of it. -Then I top the 20 bar O2 with air to desired Nitrox. This premixed Nitrox goes into compressor and diving cylinder. So no need for a nitrox stick.

put the tanks on a rack laying sideways

 

[Agro]

We are talking about 50 lt 100 kg tanks.

 

[NAM001]

I have never understood the issue of stratification. No explanation given for it removes teh concern from an air bank of air stratifying. I can visualize perhaps tri mix being a problem but not a nitrox atmosphere. I would also think that any tank of nitrox based gas would be so fragile to stiring that one should never have a problem. A short shot of gas in or out would stir it up again. I guess I just done understand what actually causes the statification or the time to stratify especially when it applies to a nitrox mix where the 2 gasses are so close to the same weight. Perhaps I have never been involved with any source that has had the time (what ever it may be) to stratify. I have heard of those blending at home and testing the tank, getting one reading,and,then getting another one later at the dive site. I have tried to test a tank that has sat for months unmoved and at the dive site i get the same reading +/- .2. I have also done the same thing with a pair of tanks that have been sitting for months. rolling one around and stirring, then testing both. The difference is not mentionable when its .1 or so. I write that difference off as an issue with the testing device.

 

[Agro]

Just made a new test with 50 lt cylinders. They are about 6 foot / 1.8m tall.
35 bar of oxygen, topped by air, should get a 29 Nitrox.
- Cylinder A, no dip tube. Right after air top I measured 22% of oxygen. After 1 week I measured 25%. Short shot of gas, I measured 25% again. I layed down the cylinder for 1 day, I measured 29%.
- Cylinder B, dip tube. Right after air top I measured 28%. After one week I measured 28 again. Short shot of gas, I measured 29%. I layed down the cylinder for 1 day, I measured 29%.
- Cylinder C, dip tube. Right after air top I measured 28.2%. Immediately one shot of gas, I measured 29%. After 1 week 29%, after laying down 29%.

1) Stratification on Nitrox does exist and does not pass within 1 week.
2) One short shot through a bottom ended dip tube make a perfect mix within seconds.
3) A short shot without dip tube does not help at all.

Next test will be done by heating the cylinder after filling. Thanks for this idea.

 

[Akimbo]

Next test will be done by heating the cylinder after filling. Thanks for this idea.

Just be sure that the cylinder temperature cools after filling and before heating the bottom. Alternatively, a cold wet blanket applied to the top of a hot cylinder would serve the same purpose.

 

[-JD-]

Just be sure that the cylinder temperature cools after filling and before heating the bottom. Alternatively, a cold wet blanket applied to the top of a hot cylinder would serve the same purpose.

Also saves time and energy ...

 

[ScubaWithTurk]

I have never understood the issue of stratification. No explanation given for it removes teh concern from an air bank of air stratifying. I can visualize perhaps tri mix being a problem but not a nitrox atmosphere. I would also think that any tank of nitrox based gas would be so fragile to stiring that one should never have a problem. A short shot of gas in or out would stir it up again. I guess I just done understand what actually causes the statification or the time to stratify especially when it applies to a nitrox mix where the 2 gasses are so close to the same weight. Perhaps I have never been involved with any source that has had the time (what ever it may be) to stratify. I have heard of those blending at home and testing the tank, getting one reading,and,then getting another one later at the dive site. I have tried to test a tank that has sat for months unmoved and at the dive site i get the same reading +/- .2. I have also done the same thing with a pair of tanks that have been sitting for months. rolling one around and stirring, then testing both. The difference is not mentionable when its .1 or so. I write that difference off as an issue with the testing device.

I think you might be a bit confused here. The issue with stratification occurs when blending. I have found that once the mix homogenizes, it stays that way. It does not separate over time. I played hell getting 4 cylinders of 50% to be 50%. I kept getting odd readings. I laid the down and tested all 4 a full 24 hours later and they were all dead nuts.

The dives these were to used for got canceled. They sat in the compressor room for five months before they were finally used. When analyzed, they were still dead nuts.