posted by pierdive on Jul 15
Scuba tanks are filled with compressed air. Most of the time this mixture is roughly 21 percent oxygen and 79 percent nitrogen, the same mixture we breathe on land. Tanks may be made out of steel or aluminum and most often hold 80 cubic feet of air at 2000-3000psi. All scuba tanks have a pillar valve which allows a regulator to be connected to the tank and control the air flow.
Aluminum cylinders are less expensive than steel and have been known to last for 20 years with standard regular maintenance. The drawback is that aluminum cylinders they are neutrally buoyant when full, and positively buoyant when nearing empty. This means that as your dive progresses you will spend more time and air to maintain your depth. You will also need to carry more weight.
Steel tanks while being heaver on land maintain negative buoyancy when full and neutral when nearing empty. Some also accept higher pressure fills which will give you more capacity for a longer dive.
All scuba tanks are regulated by the U.S. Department of Transportation and other similar foreign agencies and regulations require that tanks undergo periodic visual inspections and pressure tests.
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