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>Chris
>
>This is a ridiculous post. There is no secret to gas mixing or blending.
Please dont make out 
>like its some sort of voodoo. If you have questions about gas blending the
best source for 
>information would be CGA located in Alexandria. VA. Call information for
the number.  If you 
>not satisfied with them then call Air Products and speak with one the
engineers.
>
>Alex
>

Granted, there is no great mystery to partial pressure blending, which is
what nearly everyone is doing to mix either nitrox or Tri-Mix.

But I am not trying to build a partial pressure blending equation.
I am trying to build one that takes into account the compressibility of each
of the gases as well as the temp rise in the cylinder. If you can show me a
program that already does this, Please send me in that direction. So far I
have not been able to find such a beast.

The gas companies can give you a very precise fill based upon standardized
tables they have developed over the years. They know their cylinders, and
they know exactly what to add to give you your desired blend.

Dive shops can either fill by partial pressure, and check for O2 as a
partial verification of final contents or fill by molecular weight if they
have the proper scales to do so (and I have only seen 1 shop that does that.)

If we are able to come up with some decent examples of what people are
doing, then we should be able to tune this little program to offer a third
option, the first that will take into account what is happening inside of
the cylinder during the fill.

Molecular weight is probably the best route, as it is independant of temp
and compressibility.
but the scales are not cheap, and commonly not made to stand up to cylinders
being place upon them.
Though I did find a manufacturer that offer a scale with 0-120 lb range, and
accuracy of 1.0 grams who claims it is fully industrial and should stand up
to having steel cylinders "dropped" on it on a regular basis, and all this
for the low price of $1,250.00



Christopher M. Parrett, President, Abysmal Diving Inc.
Makers of ABYSS, Advanced Dive Planning Software.
6595 Odell Place, Suite G. Boulder CO, 80301
Ph, 303-530-7248, Fx, 303-530-2808
ftp://abysmal.com/users/abysmal http://www.emi.net/gulfstream/abyss/abyss.html

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