The air tank or scuba tank is a cylindrical (sill-LIN-drih-cuhl) metal container used to safely store high pressure air for breathing. Scuba cylinders are available in a variety of sizes and pressure ratings. Their capacities are stated in terms of the number of cubic feet of compressed air they contain. Common sizes of tanks are thirty-eight, fifty, seventy-one, and eighty cubic feet. The regulator consists of the hose and mouthpiece used for breathing underwater. It is a simple and reliable device with only a few moving parts; yet it reduces the high pressure air in a scuba tank to a usable level and delivers the air only when it is needed and at a pressure exactly equal to the surrounding pressure. Regulators come in single and double hose models, though the single hose model is most often used in sport diving. For more information about scuba regulators and air tanks, contact a diving instructor or a sporting goods shop in your area.