Short Air Fills

[bug catcher]

Does anyone know approx. how much cubic feet of air is lost on a short fill of say 2700lbs. on a Alu. 80cf tank? I have a HP 130cu and read somewhere a fill of 3000lb being 440lb light would only give me approx. 90cf so I wondered if the reduction on a Alu. 80 would be proportionately the same? On a shallow dive I don't mind the short fill but I hate to loose bottom time on a paid charter. I know to tell the shop to fill slower (and I have) but it don't sink in and they won't put the tanks in cooling water. Thanks in advance!

 

[nimoh]

Al 80:
80cuft/3000psi = 0.02667 cuft/psi

0.02667 cuft/psi * 2700 psi = 72 cuft (i.e you are losing 8 cuft of gas with the short fill)

HP 130:
130cuft/3442psi = 0.03777 cuft/psi

0.03777 cuft/psi * 3000 psi = 113 cuft (i.e. a little better than 90 cuft)

 

[mala]

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).

 

[nimoh]

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).

the math is so much easier in metric (I had to use a calculator for my answer)

 

[mala]

the math is so much easier in metric (I had to use a calculator for my answer)

you cant take a calculater underwater.

 

[Peter_C]

Most of it is simple math.
130/3442=.03776x3000=113
An AL80 is actually a 77cf tank.
77/3000=.025666x2700=69

Leave the tanks for a longer period of time at the dive shop and do not wait on them. Then when you go to pick them up they can top them off. No need for cooling water, and many will argue the cooling water can get into the tanks.

 

[nimoh]

you cant take a calculater underwater.

I agree, but you should probably know how much air you have before going underwater

 

[mala]

I agree, but you should probably know how much air you have before going underwater

i do.
its the op that was asking the question.

you just never know what might happen underwater and when a quick calculation might just safe your life.


if i had to work out cu/ft ,psi,water depth in feet and sac rate in whatever you use i would be lost.

 

[nimoh]

i do.
its the op that was asking the question.

you just never know what might happen underwater and when a quick calculation might just safe your life.


if i had to work out cu/ft ,psi,water depth in feet and sac rate in whatever you use i would be lost.

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.

 

[dfx]

the math is so much easier in metric (I had to use a calculator for my answer)

It's quite easy to answer the OP's question without calculator. When 3000 psi give you 80 cu ft, then 300 psi give you 8 cu ft.

80 - 8 = 72.