Re: Gas calculations
"...I know my tidal rate is 18l per minute. So 36l at 20m..."
Just noticed this. You might want to check your maths there. 20m = 3bar, not 2.
Mind you, I'm making assumption myself that when you say tidal rate, that you mean surface air consumption?
If also suggest you rethink you're buddy having smaller cylinders.. what happens if you need to share gas? You should always cater for the heavier breather