A scuba tank, also called a scuba cylinder, is constructed out of either steel or aluminum. Aluminum tanks are more common and less expensive, but more prone to denting and wear. Most dive shops will only have aluminum tanks for rent, so it is good to become familiar to their size, weight, shape and buoyancy. (See the creation of Aluminum cylinders: www.youtube.com/watch?v=qAgSU6BCpsY)
Steel scuba tanks are more expensive, but they are far more durable. It is said that a properly maintained steel scuba tank will last longer than the diver who wears it. The caveat with a steel scuba tank is that it will rust, and a steel tank user needs to periodically inspect their tank for the rust; but rusting can be avoided with proper care. (See the creation of the steel cylinders:
http://www.youtube.com/watch?v=EzVogfVxXPc&feature=related)
Whether you get an aluminum scuba tank or a steel scuba tank, regardless of the actual physical dimensions of the scuba tank, when you get your tank filled, it will be filled to 3000 psi. The capacity of your scuba tank is measured in pressurized cubic feet; in other words, how many cubic feet (or liters) of air can be stored in the tank at 3000 psi? An average tank holds about 80 cubic feet of air, though tanks range in size from 6 to 120 cubic feet. The extra-small scuba tanks, the 6 cubic foot, "pony tanks," could be used in an emergency situation. (See the Scuba Physics http://www.thescubaguide.com/certification/physics-of-diving.aspx section for explanations).
The size of the scuba tank or tanks you need, is decided by the amount of air you will need. If you are a teen or a petite woman you will be fine with a smaller scuba tank. An average adult will take an average (80 cu.ft.) scuba tank. Larger men, who breathe deeply, might need a larger scuba tank, or a pair of scuba tanks, if available.
An 80 cu.ft. scuba cylinder, at 3000 psi, contains 80 cu. ft. of air, which is about the size of a telephone booth. The air in a telephone booth at 14.7 psi (or 1 ATM, which is ambient sea-level air pressure) weighs about 6.5lbs. The air is compressed 204.08 times smaller to fit into the scuba cylinder.
3000 psi / 14.7 psi = 204.08 - www.crazyscuba.com
The compressed air in the scuba tank weighs 6.5lbs, which is why you can feel the weight difference between a full tank and an empty tank.
Pony Scuba Tank
Another kind of scuba cylinder, becoming increasingly popular, is the pony scuba tank. A pony scuba tank is a little extra scuba tank, which straps to your gear, and has a separate regulator. It’s use is in case your equipment malfunctions, or you misjudge your air consumption. www.crazyscuba.com
