High pressure cylinders for storing carbon dioxide (CO2) gas or a mix of gases are used for a variety of purposes, including custom aquaria, SCUBA diving, beer brewing and paintball sports. Most importantly, fire extinguishers are often CO2 cylinders, and must be inspected regularly in order to ensure home safety. According US Department of Labor Occupational Health and Safety Administration regulations, CO2 cylinders should be tested once every five years by a facility certified by the US Department of Transportation.
- Skill level:
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Things you need
- US Department of Transportation certification to conduct testing
- Valve wrench
- Hydrostatic water jacket type testing chamber
Depressurise the CO2 cylinder by opening the valve slowly and releasing the pressurised CO2 gas.
Inspect the exterior of the cylinder for any signs of rust or corrosion. Discard compromised tanks.
Remove the valve from the cylinder and visually inspect the interior for any signs of rust or corrosion. Use the flashlight to ensure good visibility. Discard compromised tanks.
Place the empty, open cylinder into the hydrostatic wet-jacket testing chamber.
Attach the pressurised water inflow valve to the top of the cylinder and seal the chamber.
Fill the chamber with water at normal pressure.
Slowly fill the cylinder with water under pressure to 5/3 of the working capacity specified in the DOT stamp (see Resources) on the neck of the cylinder. For example, a 1,000 psi (pounds per square inch) cylinder should be filled to 1,667 psi (1000 x 5/3).
Monitor the water level in the burette as the tank fills. The burette is the clear glass tube with increment markings (ml) that is located on the outside of the chamber. As the pressurised cylinder expands inside the chamber, it displaces water into the burette. Record the water level in the burette at 5/3 pressure (e.g. 100ml).
Slowly release the pressure from the water cylinder. Record the water level in the burette after the cylinder pressure is released (e.g.10 ml).
Approve the hydrostatic test for the cylinder if the water level in the burette after pressure release is ten per cent or less of the water level in the burette at maximum pressure; otherwise the cylinder did not return to normal size and you should not certify the cylinder.
Label the cylinder with the name and signature of the person performing the test, the test date, and the serial number of the cylinder tested.
Tips and warnings
- Contact fire extinguisher inspection services, SCUBA diving shops, aquarium supply houses, and paintball speciality shops to find the best price for inspection. If they offer this service, they will have certified inspectors on staff.
- Use your knowledge of the testing process to ensure that your tank is tested properly and that you understand the test results.
- Do not attempt to inspect, hydrostatically test, or fill your CO2 tank unless you have the proper certification to do so.
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