Old air in tanks.

[Patoux01]

The O2 you put on top of the air behaves basically like the gin.

Common sense is to put air on top of O2 imo. That way you don't need very high O2 pressure (for basic nitrox that is. eg put 50b of O2, top up with air. Instead of putting 150b air and topping up with O2 which now requires O2 at 200b)


So that story of reading 80 on a tank blended to 50 seems odd to me.

 

[dberry]

Maybe he has a really long dip-tube...

 

[Storker]

Or maybe he fills air first, then O2. Or either.

EDIT: I only blend continuous, but I can easily imagine myself filling a tank with air first, then O2. At least for me, the math is simpler that way.

 

[Patoux01]

At least for me, the math is simpler that way.

Wait, what?

 

[Storker]

It's how I've set up my spreadsheet. And the uncontrollable variables are residual pressure and mix in my tank.

 

[Patoux01]

But still, it's quite unlikely that the only thing you do is "top up on O2".

Anyway, simply, here around, most people prefer not having to boost their O2, so they only do it when necessary, hence why they put O2 first, it requires lower pressures.

While I really can't see a benefit to doing it the other way. What is the output of your spreadsheet? It's simply "bars of O2" and "bars of air", no?

 

[Storker]

But still, it's quite unlikely that the only thing you do is "top up on O2".

Anyway, simply, here around, most people prefer not having to boost their O2, so they only do it when necessary, hence why they put O2 first, it requires lower pressure

Isn't that how GUE et al. do it with tmx and standard mixes? EAN32 to a given pressure, top up with He?

 

[KeithG]

I guess you're talking about pp blending here. It's a bit like when you mix yourself a G&T by filling the glass half full with ice cubes and tonic water, splashing some gin on top and immediately taking a sip. The gin is sitting on the top with only a little tonic water mixed in, so the sip won't be properly blended. Stir it with a spoon or let it sit long enough for the diffusion to do its job, and it'll be very nice. Except if you decide to wait for the diffusion, all the ice will have melted and your nice G&T will be lukewarm.

The O2 you put on top of the air behaves basically like the gin. And the valve is at the end of the tank, so your gas isn't a mixture from all places inside the tank. At high pressures, the viscosity of gas is rather high, and diffusion is rather slow. But the mixing due to handling of the tank after the fill, and the time for diffusion will do their job, and when you have the same mix everywhere in the tank the gases won't separate again.

I like the explanation.

So where do we get the tanks full of gin?

 

[Patoux01]

Isn't that how GUE et al. do it with tmx and standard mixes? EAN32 to a given pressure, top up with He?

I think they do, but I'm not too scared of helium in a compressor. Oxygen on the other hand...

 

[Doby45]

@Patoux01 is correct about a PP blend. O2 goes in first at the lower pressure. This also allows you to get more use of an O2 tank before needing a booster.