Scuba divers carry their air supply in tanks on their backs. Because scuba tanks hold compressed air, they allow recreational divers to stay underwater for an hour or more at a time. Most modern scuba tanks hold compressed air or other breathing gases at pressures up to 3,000 psi, or pounds per square inch.
History
MarineBio.com credits Benoit Rouquayrol and Auguste Denayrouse with the invention of the first tank that could hold compressed air. Rouquayrol and Denayrouse’s tank could hold air at pressures up to 250 to 350 psi. In 1933, Yves Le Prieur improved on Rouquayrol and Denayrouse’s tank by developing a high-pressure tank that could hold air at pressures up to 1,500 psi. Le Prieur’s tank also delivered air to the diver on demand rather than in a continuous flow.
Pressure Reduction
You cannot safely breathe air at pressures of 3,000 psi. Your regulator reduces the pressure of the air in your tank to a breathable pressure. According to scuba-diving-smiles.com, the regulator’s first stage reduces the air’s pressure to about 150 psi, and the regulator reduces the pressure even further to a breathable pressure. As you breathe more of your tank’s air, the pressure of the air in the tank decreases. Balanced regulators will continue to deliver air at a constant pressure even as the pressure of the air in the tank decreases. Unbalanced regulators will begin to deliver air at lower pressures as you continue diving.
Monitoring Pressure
You must monitor the pressure of the air in your tank throughout your dive. You can monitor your tank’s air pressure with the pressure gauge attached to your regulator or with a dive computer. When you notice your air pressure getting low, you know you have less air left in your tank to breathe. You should ascend with plenty of air left.
Tank Markings
A tank’s markings must clearly indicate the pressure it can safely hold. When scuba tanks undergo hydrostatic testing, the technicians will test the tank at five-thirds the pressure it normally holds to ensure that the tank can safely hold such pressure. The tank’s markings will indicate the tank’s working pressure and its test pressure, often in bars rather than psi. For example, 200 bars equal 3,000 psi.
High-Pressure Tanks
Scuba tanks that hold compressed gases at pressures exceeding 3,500 psi require a different kind of valve. According to underwaterdivingequipment.com, these high-pressure tanks require DIN valves that provide a more secure seal around the O-ring. Unlike the more common A-clamp or yoke valve, the DIN valve allows you to screw the regulator directly into the tank’s valve, surrounding the O-ring completely. With a-clamp or yoke valves, you tighten the regulator’s connection with the O-ring indirectly with a knob.
Member Comments
nathanS2 February 28
My only concern with this, which seems to be a common trend in the industry, is the idea that all modern tanks can be filled to at least 3000 psi - this is simply not true, 2400 psi tanks (almost all steel tanks) are 2400 psi, not 3000, even though many shops treat them the same. I fill many of these every day, but I won't fill them past their rating - in the first five years, 2400+ tanks can be filled to 2650, but other then that, 2400 can't be exceeded for those tanks. Aluminums, the more common type of tank, are pretty much all 3000, but these are not the only tank types.