- 1). Read the imprinted markings near the tank valve (crown markings) and locate the tank pressure, usually in psi and specified as a four-digit number. For example, the crown marking for 3,000 psi can be "3000PSI" or "3000" on the top line (closest to the valve).
- 2). Determine what material your tank is made of: aluminum or steel (this is also stamped on the tank, such as "Al" for aluminum).
- 3). Check whether the volume is included in the crown marking; it is usually with the material stamp. For example, "Al65" designates an aluminum tank of 65 cubic feet.
- 4). Measure the height of the tank (not including the tank valve) and its diameter if the volume is not stamped.
- 5). Check the diameter and height against the following tables of standard sizes for scuba tanks if your tank is made of aluminum:
ALUMINUM
Height (inches) - Diameter (inches) - Volume (cubic feet)
20 to 21 - 7.25 - 63
26 - 7.25 - 80
26 - 8.00 - 100 - 6). Check the diameter and height against the following tables of standard sizes for scuba tanks if your tank is made of steel:
STEEL
Height (inches) - Diameter (inches) - Volume (cubic feet)
17 - 7.25 - High pressure 65
20 to 21 - 7.25 - High pressure 80
24 - 7.25 - High pressure 100 or low pressure 80
24 - 8.00 - High pressure 119 or low pressure 95
26 - 7.25 - Low pressure 85
26 - 8.00 - Low pressure 104
28 to 30 - 7.25 - High pressure 120
28 to 30 - 8.00 - High pressure 130 or low pressure 120 - 7). Perform the following check if the above table shows that your steel tank volume can be either high pressure or low pressure, based on dimensions: Attach your regulator set up to your tank and turn it on; check your pressure gauge and if the reading is 3,000 psi or less (with a standard, full tank), it is a low-pressure tank.
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