Quote Originally Posted by snock View Post
He created this spreadsheet so that anyone can input the appropriate data to find out how many fills per scuba tank they'd get from their kit.

How many fills.
That’s a reasonable first guess but a little naïve. It assumes that air is infinitely compressible and behaves as an Ideal Gas . Unfortunately, that is not the case. Consequently, the model will slightly underestimate the number of fills if the bottle pressure is less than ~232 Bar and progressively overestimate if it is greater.

e.g.,

‘Calibrating’ the spreadsheet with bottle volume=6 Litre, Bottle Pressure=232 Bar, Rifle Fill Pressure = 200 Bar, Rifle Bottle Volume=200 cc (AA S410 Standard), ‘Empty’ Pressure = 120 Bar and ‘Standard’ hose type (10 cc) gives an estimated 10 fills. Changing the only Bottle Pressure to 300 Bar suggests 33 Fills.

Entering the same data into FillCalc (which has the Van de Waal corrections applied) yields 10 fills and 24 Fills @ 232 Bar and 300 Bar respectively.

I guess that most folk use 232 Bar bottles anyway (so the increasing discrepancy above 232 Bar is fairly academic) but please be aware that, if you’re considering a 300 Bar set-up, you’ll get considerably fewer fills than this spreadsheet suggests.

ATB
Dave