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TexasScuba53
10-13-2008, 14:19
Just returned from Coz and had a problem with Nitrox fills. Was told it was my analyzer and that if Nitrox sits in a tank for an extended period the nitrogen will separate from the oxygen. Has anyone ever heard of that? BTW, the tanks had only set for about a week. Tanks were filled to about 3200 psi and the process used in Coz is Partial Pressure Blending.

texdiveguy
10-13-2008, 14:27
Look familiar...........

Nitrox gas separation - ScubaBoard (http://www.scubaboard.com/forums/advanced-scuba-discussions/256022-nitrox-gas-separation.html)

After 6 pages and some 56 replies did you not get the answer? What info. are you looking for.

jbanks27
10-13-2008, 15:31
Just returned from Coz and had a problem with Nitrox fills. Was told it was my analyzer and that if Nitrox sits in a tank for an extended period the nitrogen will separate from the oxygen. Has anyone ever heard of that? BTW, the tanks had only set for about a week. Tanks were filled to about 3200 psi and the process used in Coz is Partial Pressure Blending.

Not a bit of truth to it. The only thing you may run into is if water is in the tank and it sets for a period of time, you may run through a process where through the corrosion it can reduce the oxygen percentage inside the tank.

Also, Oxygen is a base element... It isn't combined with anything. You read about O2 not O1....LOL....

WebElements Periodic Table of the Elements (http://www.webelements.com/) You can clearly see that Oxygen, Nitrogen, Helium, Neon, etc.. are seperate elements.

TexasScuba53
10-13-2008, 15:31
Just wanted to see what kind of interest I could generate over here. Didn't know there was some unwritten rule about posting the same thing on multiple boards!!!

No Misses
10-13-2008, 15:31
No. the gasses will not seperate due to storage. If you are partial pressure blending and your measurment does not match what you calculated it to be - check your math - if you don't see any errors, dump the mix and start again.
Two things (there are more) that can throw off your mix.
1. Rust in a steel cylinder can lower your FO2 over time.
2. Combustion! If your valve is not properly cleaned for O2 service you may have had a small fire during O2 pressurization. Not only will this lower your FO2, it will create CO2. This is Bad Ju Ju.
If you do not understand the value of properly mixed gasses, stay away from the Voodoo Gas :-)

texdiveguy
10-13-2008, 16:51
Just wanted to see what kind of interest I could generate over here. Didn't know there was some unwritten rule about posting the same thing on multiple boards!!!

No unwritten rules....just thought it had been explored to crazyness on the other board. Air is nitrox and will not separate in your scuba cylinder!

in_cavediver
10-13-2008, 20:29
As others have said - they will combine not separate. The only time you might see stratification is immediately after blending a relatively high F02 mix via PP and using good slow fill rates. This too will correct itself over time. Rolling also helps expidite the process.

The ideal gas laws say statification can't happen but I have personally seen it done and replicated. Two tanks - both 50/50 O2. Immediately after topping off - both read around 75-80% o2. Roll one for 5 minutes - it reads 51%. The other still reads 75%. 24 hours later, one is 51% the other is 50%.

monant
10-14-2008, 06:58
Seems that if the gasses would seperate in a tank, they would also seperate in any room with no air movement.

TexasScuba53
10-14-2008, 10:04
[quote=texdiveguy;235751][quote=TexasScuba53;235727] explored to crazyness on the other board. quote]

I agree. Pretty typical on the other board!!

in_cavediver
10-14-2008, 17:45
Seems that if the gasses would seperate in a tank, they would also seperate in any room with no air movement.

Well - gases really can separate its just in normal conditions - they don't. Case in point - a centrifuge. The heavier the gas, the further it will be 'thrown'. You can also see some of this with vastly different gas weights. For diving though - the needed conditions for this to happen just aren't achieved for what we breathe, even for He in trimix. Now, throw in some gaseous Uranium and you'd likely be able to get an effect.

Grin
10-15-2008, 08:27
As others have said - they will combine not separate. The only time you might see stratification is immediately after blending a relatively high F02 mix via PP and using good slow fill rates. This too will correct itself over time. Rolling also helps expidite the process.

The ideal gas laws say statification can't happen but I have personally seen it done and replicated. Two tanks - both 50/50 O2. Immediately after topping off - both read around 75-80% o2. Roll one for 5 minutes - it reads 51%. The other still reads 75%. 24 hours later, one is 51% the other is 50%.

I was going to say the same thing. I have seen this many times. When a partial pressure fill is done, then you try to verify the mix right after the blend is done, I am never suprised when the mix seems way off. I just roll the tank around on the floor for a few minutes and recheck. Result is the perfect requested mix measurment.

So all this is the exact oppposite of this separating topic, which is a funny scare topic someone came up with somewhere out in internet land. Next thing you know the atmosphere will start to separate and we'll all die :smiley11:

in_cavediver
10-15-2008, 11:35
As others have said - they will combine not separate. The only time you might see stratification is immediately after blending a relatively high F02 mix via PP and using good slow fill rates. This too will correct itself over time. Rolling also helps expidite the process.

The ideal gas laws say statification can't happen but I have personally seen it done and replicated. Two tanks - both 50/50 O2. Immediately after topping off - both read around 75-80% o2. Roll one for 5 minutes - it reads 51%. The other still reads 75%. 24 hours later, one is 51% the other is 50%.

I was going to say the same thing. I have seen this many times. When a partial pressure fill is done, then you try to verify the mix right after the blend is done, I am never suprised when the mix seems way off. I just roll the tank around on the floor for a few minutes and recheck. Result is the perfect requested mix measurment.

So all this is the exact oppposite of this separating topic, which is a funny scare topic someone came up with somewhere out in internet land. Next thing you know the atmosphere will start to separate and we'll all die :smiley11:

If you want to dig deep enough - you can start doing molecular calculations and gravititational effects with energy blah blah blah and likely see that if you have a heavy gas and a very light gas in a open non-disturbed area, you can get some stratification. (think chlorine gas clouds or Co2 clouds). The thing is, given all of the other sources of energy and the confinement in a tank, most gases simply aren't impacted by the gravitiational force in any significant way as it relates to other gases in a sealed volume

Tassie Diver
07-02-2009, 22:33
Fart - can others smell it? This is called gaseous diffusion.

A gas will spread out to fill the space it is contained in. This is related to collisions between the molecules of the gas. (An oversimplification of a complex subject.) Given time, the oxygen and the nitrogen (and the helium) will spread out to fill the cylinder and the mixture will be, for our intents and purposes, homogeneous, ie not stratified.

Cheers

TD.

wgt
07-03-2009, 06:28
Monatomic oxygen (O1) is found higher in the atmosphere than we tend to find ozone (O3). It overlaps, actually, with low earth orbit and accounts for significant amounts of corrosion affecting low-orbiting spacecraft.

O2 and O3 are not elements, per se. Rather, they are molecules comprising more than one atom of the same element.



Also, Oxygen is a base element... It isn't combined with anything. You read about O2 not O1....LOL....

WebElements Periodic Table of the Elements (http://www.webelements.com/) You can clearly see that Oxygen, Nitrogen, Helium, Neon, etc.. are seperate elements.

Recon
07-03-2009, 12:57
I think now, I feel stupid.... ya'll are a bunch of smart people, and I thought that I knew a little something about some things.... being a network engineer.... college type guy now.... bah.... who am i kiddin' i am still a ground pounder at heart.

~Recon

acamato
07-03-2009, 23:01
The ideal gas laws say statification can't happen but I have personally seen it done and replicated. Two tanks - both 50/50 O2. Immediately after topping off - both read around 75-80% o2. Roll one for 5 minutes - it reads 51%. The other still reads 75%. 24 hours later, one is 51% the other is 50%.

The stratification you are seeing is temporary and is caused by the lack of air movement in the bottle during the fill. It takes about 1-2 hours for a partial pressure fill to mix or 5 minutes, as you said, if you roll it because you are moving the air.

IrishSquid
07-04-2009, 07:08
Fart - can others smell it? This is called gaseous diffusion.

A gas will spread out to fill the space it is contained in. This is related to collisions between the molecules of the gas. (An oversimplification of a complex subject.) Given time, the oxygen and the nitrogen (and the helium) will spread out to fill the cylinder and the mixture will be, for our intents and purposes, homogeneous, ie not stratified.

Cheers

TD.
:smilie39:

cummings66
07-05-2009, 08:02
That's one of the more unique explanations I've heard about it.