I need some mafs help. If I had a twin 7s set (14l) down at say 50 bar, and topped it back up from a set of twin 12s (24l) at say 220bar, what would I get in the 7s? This should be easy but I'm a mathstard. Trying to decide if i should ditch the 7s for a pair of 12s as a single set, just don't want to admit I need to and have the expense. Thanks buddys C

Hmmmmm. 50 bar was just a lowest pressure example. 157 wouldn't give much of a second dive, even if it is shallow rib dives. Thanks Beks

Its the equiv of around 180odd bar in a single 12, so not that bad really. Q is I guess are you going to get down to 50 bar, you'd prolly have more depending on your buddy x

yep, on a recreational dive, if I started with 14l at 220 bar i'd likely be finishing with 80 bar which is more sensible and realistic. What is the formula for working this out?

Yep thats what I thought. You can cascade as stretch says closing the manifold, but its not a huge difference. v1 = Cyl 1 size in litres p1 = Cyl 1 pressure v2 = Cyl 2 size in litres p2 = Cyl 2 pressure p3 = Settled pressure p3 = (v1xp1)+(v2xp2) I have an excel sheet with this on and some other stuff, I'll see if I can find and send it over x

This is a bit of a simplification It's. P1st x Volfirst + Psecond x Volsecond = Vol total divided by (volfirst add volsecond) So for twin twelves for the first dive and a 15 for the top up. Finish first dive on 100bar on the twins. 24x100 + 232x15 = 5880/39 = 150 bar. B

(Pressure * volume of vessel 1 plus pressure * volume of vessel 2) divided by the total volume of vessels 1 and 2