cylinder capacity

[andy j]

Are there any tables that can calculate differant amounts of air held in differant tanks in comparison to each other.
ie what cylinder would give me the most bottom time ? a 136bar 7ltr or a 300 bar 3ltr? twin 200bar 10ltr or 300bar 15ltr?

 

[Doc Harry]

Are there any tables that can calculate differant amounts of air held in differant tanks in comparison to each other.
ie what cylinder would give me the most bottom time ? a 136bar 7ltr or a 300 bar 3ltr? twin 200bar 10ltr or 300bar 15ltr?

It's a simple calculation. I only know the Imperial calculations, though. Metric is too confusing.

Volume (cubic feet) = Rated cylinder volume (cubic feet) x Actual fill pressure (psi) divided by Rated fill pressure (psi)

 

[Kern]

Multiply the working pressure in bar by the water capacity in litres for the maximum rated capacity. Or current pressure by WC for present capacity.

136bar x 7lt = 952lts
300bar x 3lt = 900lts

200bar x 10lt = 2000lt
300bar x 15lt = 4500lts

 

[devilkitty]

Beat me to it.
But a 7 litre bottle @ 136 bar holds 952 litres of gas.

 

[vicp]

Most technical dive course manuals (advanced nitrox, deco procedures, etc.) will have tables and formulas for gas management.

You can also google "understanding gas management" to find a pdf by Bob Bailey and other links to the information you want.

 

[Spimon]

I've written a spreadsheet to calculate approximate dive time. Follow this link to my website, Simon Yachting - YA/RYA Skipper and go to the 'Tools' section to find the Dive Time Calculator.
Plug in your SAC rate, tank size, tank pressure and depth and it'll tell you a theoretical bottom time.

It also includes a SAC rate calculator from dive history. Plug in your start pressure, end pressure, tank size, dive time and depth and it will give you your SAC rate. If you don't have this history from your last dive, plug in 15 l/min (I hear that's average).

7 litre @ 136 bar should give you 22.67 mins @ 18m
3 litre @ 300 bar should give you 21.43 mins @ 18m
Essentially the same...

2x 10 litre @ 200 bar should give you 95.24 mins @ 18m
15 litre @ 300 bar should give you 71 mins @ 18m

-- That's until absolutely empty, not allowing safety and ascent time -- This also assumes constant SAC rate, which may not be the case with different configurations and different conditions. All in all, it's only a mathematical model, not real life - treat it only as an estimating guide.