Anyone ever hear of tank rolling after mixed gas fill??

[do it easy]

How did draining to ambient enter the equation?

When the gas hits the meter, it is at ambient pressure, or at least close to it. So it will be cooled as the pressure drops from 3000 psi to ambient.

 

[Notso_Ken]

Ok - I'm going to come out and admit it - I've never seen this before..... ever. UNTIL we got our tanks filled at a PADI dive center down in West Palm Beach somewhere.

For those of you who don't know what I mean - after a NITROX fill, the lady who filled the tank proceeded to lay the tank down on its side, and roll it with her foot! She claimed that it helped the gases inside "mix better." :icorolley

Anyone else ever experience this? I can't believe they actually did this....

Yep, I've heard it. But, given the low viscosity of the gas (even at the high pressure), and the slow speed of the rolling, there isn't going to be enough mixing to do anything, except within a very thin layer right next to the tank wall.

As another replier already stated, the air flowing in during the fill is going to do a lot more to ensure it's mixed than rolling it will.

Ken

 

[GeekDiver]

I'll tell ya what I'll play along with this silly game.

Since O2 is lighter than nitrogen then will all the nitrogen sink to the bottom of the tank leaving only a high percentage of o2 on the top of the tank? Gee wiz if thats the case could get a tox hit due to breathing to rich a mix since all the nitrogen molecules are on the bottom of the tank leaving only o2 at the top of the tank? But wait mayby in the process of setting up your tank, reg etc and jumping in the water will cause the mix to get all stired up again.

With all the worry of the mixed gasses becoming seperated I just don't know if it'll ever be safe to breath that nasty black air call nitrox. Why if the air becomes seperated between o2 and nitrogen how will I ever now what my EAD or MOD could be. Wait I'll just make sure to role over on my back several times during the dive to make sure that the gas is mixed up real good and never gets seperated.

 

[wedivebc]

So why doesn't all the o2 separate from the nitrogen in the earth's atmosphere? Cause the world is spinning right?
I would get yourself a nice pair of steel tanks and double them up. Then let's see her roll your tank.

 

[MXGratefulDiver]

Has anyone actually analyzed a partial-pressure blended tank immediately after filling and then again a little while later to see if maybe this does actually make a difference?

Yes ... we had this discussion not too long ago. At the time I asked folks to do some empirical testing and report back the results. I have my own O2 analyzer, so I do it regularly.

There is some stratification ... not a whole lot. Depending on the mix and the speed at which the cylinder is filled, it might amount to a few tenths of a percent difference ... usually less than that.

... Bob (Grateful Diver)

 

[wedivebc]

Has anyone actually analyzed a partial-pressure blended tank immediately after filling and then again a little while later to see if maybe this does actually make a difference?

I have and the readings do change but I suspect it has more to do with cooling than stratification.

 

[DepthCharge]

This is more common than you think. And it's just as absurd as you think. Molecules pinging around inside the tank aren't likely to segregate themselves into nice layers...

I've never noticed a difference mixing nitrox..............trimix however, you do get some stratifying of gasses. Depends on how you mix too. You can get an initiallyh high O2 reading or low. Depends on if you put O2 in first, or after HE. I noticed it more when mixing in dbls. Not that I'm mixing mostly 20 cft. I don't notice it as much.

 

[SueMermaid]

Is this a joke? :laughing:

 

[CIBDiving]

Since O2 is lighter than nitrogen then will all the nitrogen sink to the bottom of the tank leaving only a high percentage of o2 on the top of the tank? Gee wiz if thats the case could get a tox hit due to breathing to rich a mix since all the nitrogen molecules are on the bottom of the tank leaving only o2 at the top of the tank? But wait mayby in the process of setting up your tank, reg etc and jumping in the water will cause the mix to get all stired up again.

have you noticed that the that the PPO2 doesn't change much going up? it stays pretty darn close to 21% well past a point I'd want to try to breath it ( or even visit ). If the 'wieght of the gas mattered ten why is there O2 in death vally? that should be full of N2.

Y'all full of it, shaking the bottle does nothing -except make you feel like you're doin a good thing. It's not a liquid - gravity ( that keeps things seperated) is overpowered by brownian motion ( which mixes it up ) You can't add to the bottle slow enough to prevent complete mixing.

 

[Scubar]

I have heard of this and apparently they do this at the shop where I get my Nitrox filled. It really never made any sense to me but if they want to do it thats fine. There may be small delta between the density of 100% O2 and air but I am sure it is well mixed from the air fill on top of the O2 as well it will all reach equlibrium as the tank temperature becomes uniform.