Why do they put the scuba tank in water while refilling it??
A scuba tank is design to hold a certain volume of air, at a particular at a particular temperature. In the US, the standard tank is an aluminum 80 CF tank. At room temperature and 3,000 psi, the tank holds 72 CF of air (yeah, I know they round up calling it 80 CF tank).
When you are filling the tank, the air and tank will become warm/hot. If you check the pressure guage while the tank is warm, it will give you a reading of X. Once the tank cools, it will give you a reading that is less than X. They put the tanks in the water in the hopes of keeping the temperature do, and filling the tanks closer to the design pressure and temperature.
Some examples that you can see...
In Mexico, many of the tanks will be sitting in the sun while on the boat. The tank may have a reading of 3,200 psi. Once you jump in the water, and the tank cools down, the new reading may be 2,800 psi without ever breathing any of the air.
I have been ice diving, the tank was acutally colder than the water. Since the water temperature was warmer than the tank, me pressure reading was slightly higher.
Dec 01, 2008 |
Aeris Atmos Lx BC