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    Extinguishers: Replacing Damaged or Improper Extinguisher Gauges Ensures Safety

    By Mark Conroy


    Fire extinguisher gauges are simple mechanical devices. A flattened metal tube is coiled inside the gauge and straightens when pressure is applied. A pointer attached to the tip of the tube displays the pressure inside the extinguisher. These gauges typically do not fail. An extinguisher gauge is replaced when there is damage or the wrong one is discovered. Here is what you need to know to ensure safety.

    On an annual basis, a technician performs a thorough examination, and that is when the problems are discovered and corrective action is taken. The technician checks the following:

    • Verifies the gauge face plate is not broken or “smoked” (sun, heat, or corrosive damage).
    • Verifies the gauge is in the operable range.
    • Verifies the rated operating pressure of the gauge corresponds with the nameplate pressure.
    • Verifies agent type on the gauge face corresponds with the agent used in the extinguisher.
    • Verifies the gauge threads are compatible with the valve body material.

    Charging Pressure

    The gauge pressure must match the charging pressure. If the charging pressure for the extinguisher is 195 psi, then the gauge must have “195” in the green area. You can find the extinguisher charging pressure on the extinguisher nameplate or in the service manual.

    Agent Type Marking

    Extinguisher gauges are marked with the type of agent. A dry chemical gauge will say “USE WITH DRY CHEMICAL ONLY”. A gauge that has the marking “USE WITH WATER, AFFF OR LOADED STREAM ONLY” can be used with any of these three agents.

    Compatability with Valve Body Material

    Check the manufacturer’s code letter before installation for valve body compatibility as follows:

    • Aluminum - A line above the gauge manufacturer’s code letter matches an aluminum valve body.
    • Brass - A line below the manufacturer’s code letter is a gauge for use with a brass valve body.
    • Aluminum or Brass - A universal gauge has lines above and below, or there is an absence of any line.

    Extinguisher Gauge Wrench

    The proper tool for removing and installing extinguisher gauges is the Brooks gauge wrench (P/N GWRENCH). It is specifically designed and will not damage the gauge and the extinguisher valve.

    An extinguisher gauge is relied upon to indicate that the unit is pressurized and ready to use in the event of a fire emergency. Using Brooks’ replacement gauges provides a reasonable assurance that the gauges will provide correct readings and the extinguisher will be ready for use on a fire.


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    Mark Conroy is an engineer in our Boston, MA office and a member of the NFPA 10 Technical Committee. © 2018 Brooks Equipment.

    Disclaimer: The opinions expressed in the above Tech Series article are the author’s only and provide limited information. Although the information is believed to be reliable, Brooks Equipment Company, LLC expressly disclaims any warranty with respect to the information and any liability for errors or omissions. The user of this article or the product(s) is responsible for verifying the information’s accuracy from all available sources, including the product manufacturer. The authority having jurisdiction should be contacted for code interpretations.