diverbrian once bubbled...
[BI have seen the trouble that the guy goes to at the one place that I have been to where he partial pressures. It is a pain ...<snip>... to do a hand calculation of each individual tank every time he is asked for a nitrox fill. He has since gone to have EAN40 preblended that he will cut with air to give the desired mix. [/B]
My LDS banks O2 compatable air, 40% (they have a DNAX compressor) and several O2 bottles for blending mixes over 40%
I, another DM and an instructor sat down one weekend and banged out a simple spreadsheet for calculating nitrox gass mixes.
We even donated to the shop an old 486 PC running win95 to run the spredsheet on.
Gas blending calcs only take a few seconds this way.
Just enter the tanks working pressure, current pressure, current O2%, fill gas O2% and topoff gas O2%. Normaly the fill and top-off mixes don't change unless we're doing fills over 40%.
The spreadsheet then fills in a chart from 21%-100% O2. for each nitrox mix it lists the PSIs needed from the fill gas and the PSIs needed from the top-off gas to acheve that mix or just shows "not possible" instead of numbers if the mix can't be achieved given the available gasses.
EG: if you are filling an empty tank using 100% O2 as a fill gas and 40% nitrox as a top-off gas, anything from 39% and lower will show "not possible".
It saves lots of gas because we don't dump the tanks to empty before filling them anymore unless it's a 40%+ mix and the O2 cascade is getting low.
