sentences:  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.APW extinguishers are commonly converted into makeshift CAFS extinguishers by drilling two holes in the pickup tube.The unit is then filled with of water and Class A foam, AFFF, FFFP or commercial detergent is added to the water in a 1% ratio for class A fires and a 3–6% ratio for Class B fires.