Air pressurized water
Air pressurized water (APW) extinguishers are a type of fire extinguisher that use ordinary water (H2O) to suppress fire. The water is propelled by ordinary air (atmosphere), pressurized in the extinguisher. They are also known by the slang term water can. Although only effective on Class A fires, they have the advantages of being inexpensive to build and maintain, and leaving no special chemical residue when used. Some APW extinguishers add a wetting agent to make the water penetrate the surface of materials quicker.
Construction
A standard APW extinguisher in the United States contains 2.5 US gallons (9.5 L) of water in a stainless steel tank. The water is discharged by means of a ½-inch hose, with a smooth-bore nozzle attached to the tip. They will initially produce a 40–50 foot stream of water, with a discharge time of about 50 seconds.
APW extinguishers are easily refilled by unscrewing the top and filling the cylinder with water about three-quarters of the way up. The top is then screwed back on, and the unit is pressurized with an air compressor via the Schrader valve located on the back of the main valve body.