Scuba Tank
A scuba tank is a pressurized metal cylinder that can
be filled with compressed air and then breathed underwater with the
help of a regulator. Once a tank is filled, it can be used for about
a week before it needs to have the air either changed or refilled. A
tank is necessary for any diver that would like to dive on their own
schedule, and they are easy to maintain.
An aluminum scuba tank is lighter than a steel one, but steel will last
longer, and take more of a beating. They usually hold between 3 and
18 liters, this is expressed with water because much more gas, which
can be pressurized more than water, can fit inside the cylinder. A 3
liter container can hold 696 liters of gas at 232 bar. Bar is a unit
of pressure measurement, atmospheric pressure at sea level is roughly
one bar.
‘Scuba tank’ is the colloquial and non-professional term
for a diving cylinder, which is what they are called by gas equipment
engineers, manufacturers, support professionals and divers. Sometimes
the mistake is made in calling them oxygen tanks, when it is actually
a mixture of gases that they are filled with, usually very similar to
atmospheric air, which is only about 15% oxygen and 70% nitrogen. Some
other mixtures with higher oxygen, lower nitrogen, or even added helium
are used as well to help with decompression and nitrogen narcosis which
is common at lower depths.