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Pin valve CO2 tanks are widely used to power paintball guns. These tanks are rated by the volume of liquid CO2 the tank contains. The smallest paintball CO2 tank is 30 grams and the largest is 20 ounces. Refillable CO2 tanks are made of aluminum. Any tank with a capacity of more than 9 ounces of CO2, or any tank over 2 inches in diameter, must be hydrotested every 5 years to ensure its integrity. It is illegal to use or refill a CO2 tank that is past its hydrotesting date. A permanent code stamped or etched into each CO2 tank, normally arranged in three rows, contains information to determine when you must perform. It is important to determine the country of manufacture and use when applying this data. CO2 tanks marketed in both the U.S. and Canada may include code information for both countries.
Reading CO2 Cylinder Codes
Read the first row of information on the crown of the CO2 tank. The designation "TC" indicates that the cylinder has been approved by Transport Canada for use in Canada. The specification "ALM" is the Canadian mark indicating the tank is made of aluminum. This is followed by a three digit number, such as 124, to denote the maximum working pressure of the tank in bars, the Canadian unit for measuring pressure. The last figure on the first row begins with the letter "T" and is the tare weight, the empty weight of the tank expressed in kilograms. An example of a tare designation is "T11.3KG."
Read the second row of information on the crown of the CO2 tank.The designation "DOT" indicates that the cylinder has been approved by the U.S. Department Of Transport for use in the United States. The specification "3AL" is the U.S. mark indicating that the tank is made of aluminum. A four digit number represents the maximum working pressure of the tank expressed in p.s.i. A manufacturer's serial number for the tank follows the working pressure. The last figure on the first row begins with the letter "M" and is followed by a four-digit number. This is the Department Of Transportation serial number identifying the manufacturer of the tank.
Read the third row of information on the crown of the CO2 cylinder. The date of manufacture, commonly known as the "Born On" date, is expressed numerically in a mm/yy format. The tank must be hydrotested every five years after this date. The next number indicates the tank's total capacity of liquid CO2. The last figure on the third row beginnig with "TW" is the tare weight of the tank expressed in pounds.
Look for retest labels or stamps. When an aluminum tank is hydrotested every five years, a retest label or stamp goes on the tank, separate from the information stamped on the crown. This indicates the month and year of the most recent retest numerically expressed in a mm/yy format. Also displayed is an RIN (Requalifyer Identification Number) to identify the hydrotest facility.
Gus Stephens has written about aviation, automotive and home technology for 15 years. His articles have appeared in major print outlets such as "Popular Mechanics" and "Invention & Technology." Along the way, Gus earned a Bachelor of Arts in communications. If it flies, drives or just sits on your desk and blinks, he's probably fixed it.