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Don't worry about the equations (other than for personal knowledge).
If you are going to mix a bunch of gas in one after, you probably won't be
able to keep any of the bottles at a constant temp, including the air that
you will top with. You will have a mix of cold o2 and he bottles going into
cold (if just dumped) or room temp dive bottles and you will have hot dive
bottles if you are really doing the mixing and tops fast. I can make 25/25
(for the local 150 ft stuff) in about 8 or 9 minutes). This yields a very
hot 3600 or 3700 that if left to cool over night is 3300 or 3400 psi. The
numbers come out of experience and vary greatly from the hand calculated and
Mixing software. In a nutshell- you will make a few mixes that don't seem to
come out correct even though you have been meticulous about the figuring.
After a while you will knock out 3 sets of dbles and 6 stages in side an
hour and a half, if you have the air in storage. If you pumping out of the
compressor this will take longer and you will have to fill to compensate for
the cool off.
I went digital for the gauges and connected all the o2 bottles together
with t's on the nut and nipple. Do the same with the he. You do not need any
of the bells and whistles that are mixing panels and othewr convulted crap.
Just pressure guages on the fill whip.
Decom's Gas mixer is pretty close, just figure in the over/under fills
due to temp. Good Luck-EZ
>As you probably know from my previous mails, I'm currently in phase of
>building my
>own home mixing station. During my search I found out very interesting
>findings about
>differencies between behavior of ideal and real gas.
>
>we all know that this is valid for ideal gas
>
> p * V = n*R*T
>and
> p1*V1=p2*V2 (if temperature is constant)
>
>And on this assumption many of us try to mix their
>Trimix.
>
>But based on Van der Waals findings for real gas it looks like this in
>reality
>
> (p+ (n*n*a/V*V))*(V-nb)=nRT
>
>where a,b are gas dependent constants
>
>when you use this formula for air and you for example calculate
>amount of air in 10L bottle you will get interesting results:
>
>Temp 20Celsius, Air
>presure 100Bar 150Bar 200Bar
>volume 880L 1242L 1562L
>
>For 200Bar we've got difference appx. 22% which is HUGE
>difference. That implies to me that using mixing methods based
>on ideal gas and part. presures are TOTALY useless. Using oxygen
>analyser we are able to check and adjust amount of oxygen quite sharp,
>but we've got no clue how much Nitrogen and Helium is in the mix.
>
>
>So I'd like know, if you are using this method. If not, which method do you
>use ?
>If yes, how you deal with these differencies between assumptions and
reality
>?
>
>
>
>Regards
>
> Jozef Gliviak
> Slovakia
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