slonda828 wrote:Once I have the true volume of the tank by measuring the volume of water that it will hold, I could then multiply that by the service pressure, and divide by atmospheric pressure (14.7 PSI). Then I should know how much air is really in there, right?
Yes, (but add the atmospheric before you divide) that will give you how much air the tank will hold...if you want to know how much is available to the diver use the following formula, since the regulator will use some amount of pressure to drive it beyond which it will fail to work.
Va = {[(Pc - Pm)+14.7] / 14.7} x FV x N
Where:
Pc = Measured cylinder pressure, psig (or service pressure)
Pm = Minimum pressure of cylinder, psig (minimum to drive reducer/regulator)
FV = Floodable Volume (scf) (have to convert from liters)
N = Number of cylinders
Va = Capacity available (scf)
You can then use air consumption formulas to figure out how long that supply will last given a certain depth, assuming you are heading for the surface at a given rate of ascent. Divers can use from 0.5 scf per minute (relaxing) to 2.5 scf per minute (freaking out cuz they just ran out of air)...