How to Read a SCUBA Tank

Inspect the top row of markings. In this row, you find a marking reading "DOT," followed by a number and two letters. This means that the tank has been certified by the U.S. Department of Transportation. The letters following will tell you what the the tank is made of, with 3A and 3AA signifying steel, and AL aluminum. Steel is more durable, while aluminum is lighter.

Inspect the next row of markings (i.e., the row closest to the valve opening). This row contains what you can think of as the heritage of the tank, as it will tell you where it came from and who made it. Going from left to right, the first item listed is the thread specification. This is important knowledge if you are buying a valve as you will need to get one that matches the tank.

The second item is the country of manufacture, usually abbreviated (e.g., US). Next is the serial number of the tank. This is important to make note of, as you can use it to track the manufacturing history of the tank this way by contacting the manufacturer to make sure there haven't been any significant defects in the model you are using.

Inspect the third row. Here you will find important specifications about the tank. The first is the minimum thickness of the tank, according to the manufacturer's standards, measured in millimeters or inches, depending on the manufacturer. Next is the weight of the tank when empty. After that is the capacity of the tank. If the tank is using the metric system, it measures the capacity in liters of water, while in the imperial system, it measures using cubic feet of compressed air. The next figure is vital, as it is the maximum capacity to which the tank should be filled in pounds per square inch (or bars of pressure). The final figure is a slightly higher number, which indicates the maximum pressure the tank should be filled for testing purposes.

Learn the history of the tank. The last row enables you to learn the history of the specific tank, which is very important for safety purposes. Some tanks will have another pressure number, but this one with a temperature following it. This shows the maximum pressure the tank can endure above a certain temperature. Next is the date of the original hydrostatic test on the tank, followed by the date of the most recent test. This is crucial knowledge, as tanks have to be tested every five years to ensure that they are still structurally sound enough to handle the air pressure.