Hydro-Testing – Low Pressure and High Pressure
Pressurized cylinders require hydro-testing at regular intervals. This test process checks the integrity of the metal cylinder. During this process, the cylinder is emptied, filled with water; the cylinder is then pressurized to check for weakness in the metal. If it passes the testing it is then labeled and or stamped, dried, filled; ready to be put back into service.
Dry chemical, class K, and pressurized water fire extinguishers undergo a low pressure hydro test. Dry chemical is tested in 12 year cycles while pressurized water and class K are tested in 5 year cycles.
CO2 fire extinguishers undergo high pressure hydro-testing in 5 year cycles.
Cylinders - SCBA, SCUBA, CO2, Cascade
Cylinders requiring high pressure testing such as those used for SCBA, SCUBA, Cascade systems, CO2, or Paintball are hydro-tested within a safety tank. These are tested in 3-5 year cycles.
You can see where this CO2 cylinder, with 4mm thick steel walls, split after being pressurized during the hydro-test procedure. The extinguisher was manufactured in 1952 and had not been tested until 1994. If this CO2 extinguisher had been tested in proper intervals of 5 years, it would have shown signs of metal fatigue sooner, and failed the hydro-test without exploding.
Fortunately, this occurred in the safety of the test tank out of harms’ way.