mass of air and correct weighting

[divetheworld]

As you breathe the gas out of your cylinders they get lighter. We are all taught back when you were a novice that you must be correctly weighted at the end of the dive when low on gas and needed to decompress. But we are never taught how much our buoyancy changes from full to near empty cylinders

The weight of air can be easily calculated

Temp Weight
deg C kg/m3 kg/l

0-----------1.293-------0.001293
10----------1.247-------0.001247
20----------1.205-------0.001205
30----------1.165-------0.001165



Air in a cylinder = Pressure (P) * water capacity (Wc)

So the weight (at 10C) = ( 0.001247 * P * Wc )

i.e. in a set of twin 12's pumped to 232 bar and then breathed down to 50bar we would loose the following weight

0.001247 * (232-50) * 24 = 5.44 kg

 

[roakey]

Waaaaaay too much accuracy.

Air & Nitrox weighs about 1 pound for every 13 CF of gas.

So an AL80 swings 80/13 = 6 pounds from full to empty.

I don't know what that translates to using those communist metric units.

Roak

 

[Rick Murchison]

divetheworld says: But we are never taught how much our buoyancy changes from full to near empty cylinders

All my students are taught the average weight of air... like Roaky, I use a very simple formula - .08 pounds per cubic foot, so a standard AL 80 holds a total of about 6.4 pounds of air (at 3100psi) - or about 5 pounds from full (3000psi - 77CF) to the end of the dive (500psi - 13CF).
Rick

 

[SubMariner]

I just think someone has far too much time on their hands.



~SubMariner~

 

[Ari]

Who called us Communists?

You Imperial freaks. And anyway, we prefer socialists.

Ari