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CO2 Fire Extinguishers

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Fire Extinguishers

Why is there no pressure gauge on a CO2 fire extinguisher? Ad by ClickUp

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3 ANSWERS

Dan Smith, former 10 Yrs Project Mgr. & VP/Mfg. of Extinguishers at Power Pak Products (1967-1977) Answered Sep 7, 2017 · Author has 1.9k answers and 794.9k answer views

Good question. First let’s explain the purpose of a pressure gauge on a dry chemical or wet water extinguisher: Fire extinguishers are intended to be serviced and recharged every time they are used regardless of the amount of extinguishing agent remaining. An extinguisher with a broken seal is considered used. The gauge is there to indicate that the original charge of propellant gas (usually compressed air) is still there at the correct pressure. If the device is leaking or has been partially discharged, the gauge will indicate that condition. CO2 extinguishers have no gauge because they are filled with liquefied CO2. C02 is a gas at room temp until it is compressed to around 830 psi. at which point, it begins to liquefy under that pressure. At that point the pressure will remain constant until the container is filled to its rated capacity (by weight), with liquid C02. As long as there is some liquid C02 in the container the pressure of the vapor above the liquid will remain at 830 psi. So: a pressure gauge will show 830 psi without regard to the actual amount of liquid C02 in the container. So: C02 extinguishers are filled by weight not by pressure. The only way to measure their contents is by weighing them. The filled weight is listed on the label.