Diminishing Returns and Gas Calcs for Cave Filled LP Tanks?

[Wibble]

It's really not bad. Say I'm 1000ft from the door at 110' and want to figure out a new usable gas volume to set turn pressure for a detour. 1000ft is about 30min swimming, conservatively. Assuming I'm sharing, I'll double my stressed rate of .75 to get 1.5 cubic ft/min. I know it's about .3ATA per 10 ft plus surface ATA, so that's 4.3 x 1.5. Call it 6.5 combined scr at depth (rounding is your friend). Times 30 is 195 cubic ft. Tank factors simplify things a lot and you only have to remember a few numbers. If I'm using 104s, that's 8. Divide it into 195 and you get 24 and change. Just round it up. Add on a couple zeros and you have your reserve, 2500. Divide your remaining gas by three and subtract from current pressure and you've got turn. All doable in your head within a minute or two with practice. It would take me significantly longer to get there in metric and I'd probably make mistakes. It's just about fluency.

Didn't understand a word of that, but you said it in such a nice way that I believe you ;-)

Of course it's about the way we've been taught. It's interesting how the two approaches, wet volume vs. full pressure volume, results in quite different ways of achieving the same ends

 

[J-Vo]

I was at a fill station a while back. There was a French girl staring at and s80. She asked me how us Americans fit 80cft of water in such a small tank after converting it to liters on her phone.

 

[AfterDark]

After you get your own compressor you can fill your tanks to whatever you wish DOT be damned. All those regulations apply only to commercial use of tanks. Buying your air from the LDS makes you and them subject to those regulations.

When you pump your own gas for your own use the tanks don't even require hydro testing.

You get decide what you do with your tanks, priceless.

 

[happy-diver]

When they're made of steel