air vs Ean21 and tanks

[ckharlan66]

I have been wondering what is the difference between filling a tank with air and ean21. I know the different ways that it is done but I am not sure as to why if you have a nitrox tank you can't put air in it since ean21 is the same mixture as air would be. I know to put pure O2 in you have to have a O2 clean tank but why does air ruin this?

I am not sure if the way this is worded makes since but It was the best I could do. I may be way off base with my premise but I hope you all can help me expand my knowledge.

Chad

 

[The Chairman]

It's just a cute way of saying it is NOT enriched. That being said, many shops use "hyper-filtered" air when doing their NitrOx fills and less filtered air for the other fills. They put the right partial pressure of O2 in and then fill the rest with this hyper-filtered air. The hyper-filtered air meets very stringent requirements for contaminants. Some compressors can not give clean enough air to be used with partial blending. Consequently, it is this less clean air that will "ruin" a cylinder, not the 21% mix. When I run air (which is seldom), I have them use the hyper-filtered air to keep my tanks free of contaminates.

 

[ckharlan66]

Ok so if they are using the hyper filtered air then they don't have to do the partial blending?

Chad

 

[Drew Sailbum]

Originally posted by ckharlan66
Ok so if they are using the hyper filtered air then they don't have to do the partial blending?

Chad

Sort of exactly... if that makes any sense

If you want EAN21 in your oxygen clean tanks, most shops will just pump in hyper filtered air. There is no blending involved. Since any contaminants have been filtered out, your tanks are still in an oxygen clean condition

It is theoretically possible to mix EAN21 using partial pressure blending of pure oxygen and pure nitrogen. It would be a rather costly way to go about it, and I've never seen a shop that would do it that way.

 

[ckharlan66]

Thanks guys. It's all so clear now.

Chad

 

[The Chairman]

You do not need to partial blend EAN 21 or air. If a shop does partial blending (as mine does) then yes... you need an O2 clean tank for NitrOx. Pure O2 is put into the tank first... then air is put on top to finish it. See if you can follow this... and know ahead of time I am using IDEAL gas laws and not the REAL gas laws.

If I have a 3000 psi tank with 0 psi in it (in a vacuum, even) and put 575 psi of O2 in it, and then fill it with 2425 psi of air then I will have EAN 36.

(575*1.00)/3000=19.2%
(2425*0.21)/3000=17%
19.2%+17%= 36.2%

Again, these are figures for an "IDEAL" gas which does not exist. Those that actually blend can probably give us the "fudge" factors to get the perfect blend. While I will not have time to take a blender's course this summer, it IS on my list of things to do.

 

[ckharlan66]

Thanks Pete,

I know how that was done but my mind wasn't making the connections for air and ean21. Now you guys have put me on track and I appreciate that.

Chad

 

[Ron Brandt]

The next time you walk into the shop and ask for a regular air fill in your O2 cleaned tank and the smart ass fill jocky won't do it , just tell him you want EANX 21.

Ron

 

[Walter]

Unless you are adding a minute amount of O2 to go from 20.95% to 21% there is no EAN 21. Air is nitrox, but it is not "oxygen enriched."

 

[CincyBengalsFan]

How come some of you guys don't work at a dive shop? You are SO knowledgable. Define "Hyper-Filtered"Air. Are you simply talking about pulling all the hydro carbons out of the air which SHOULD be done anyway. Hydro Carbons are the things YOU don't want to have come in contact with O2.