Short Air Fills

[mala]

Well, isn't this thread just getting a bit hijacked, so I only have one more comment.

I don't see anywhere in the original post asking how to do this calculation underwater, but in any case, I wouldn't bother with either the metric or imperial calculation to save my life on a dive, I would be heading for the surface hoping I (and my buddy) have enough air for the journey.

the op asked how to do the calculation above water.

for recreational diving i guess it doesnt matter much.

if you were sharing air with your buddy and had a bit of deco it would be handy to do the maths rather than end up on the surface heading for the chamber.

do the maths and save yourself the stress of hoping you have enough air.


i'm not having a dig just airing a few thoughts.

 

[bug catcher]

Thanks everybody! I got the calculations in my log book so I don't forget!

 

[Hatul]

i can do the metric maths .

just multiply the size of tank by the pressure.

so a 12ltr at 200 bar has 2400lts of gas.

at 190 bar it would have 10 x 12lts less.(2280lts).

Yeah, but here in the US we all breathe in cu ft, not liters. The commies breathe in liters.

 

[eelnoraa]

In one of my class, we are taught to remember "tank factor" for the tanks we commonly use. Tank factor is defined as cf of air per 100psi.

Here is a few tanks that I commonly encouter, so I remember these

AL80: 2.5 ( ~=77cf/3000 * 100)
HP100/LP80: 3.0 (~=100/3442*100 or 80/2640*100) You get the idea
LP85: 3.2
LP95/HP120: 3.5

Then it become easy to estimate how much gas is available by a quick glance at the spg.

 

[cascas]

Glad I do metric... Much easier...

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[dfx]

Glad I do metric... Much easier...

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Not really. There's always three values involved: internal tank volume, max pressure, and amount of air. The only difference is that with metric, they usually tell you the first two and you have to calculate the third, while with imperial units, they tell you the last two and you have to calculate the first. I don't see how either way is inherently easier or harder. The only advantage metric has is that atmospheric pressure is an easy "1.0" number instead of an awkward "14.7".

Sent from my stationary Linux PC using Firefox.

 

[cascas]

The only advantage metric has is that atmospheric pressure is an easy "1.0" number instead of an awkward "14.7".

that is more than enough... ;-)
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[rhwestfall]

[h=2]Okay, since the "hijack" happened - I use this: MARTEK NASDS SCUBA TIME CALCULATOR. A wonderful device from the 1970's that I happen to have. Wish they were still made.....[/h]

 

[Paladin]

An AL80 does not contain 80 cubic feet of air. It holds 77 cubic feet.

 

[Peter_C]

An AL80 does not contain 80 cubic feet of air. It holds 77 cubic feet.

At 3,117 psi it does contain 80cf! Although I am not for overfilling aluminum tanks.

On the other hand my HP130's...well lets just say fortunately my regs are rated for 4,200 psi, but I never go that high.