A compact, stand-alone fire-extinguishing system for use with a water source is disclosed. The fire-extinguishing system can include an engine, a pump, a foam tank, a flow meter, and a foamant adjustment valve. The flow meter can be a variable area flow meter and indicate an instantaneous concentration of a water-foamant solution. The foamant adjustment valve can be a needle valve. A head injector can be coupled to the pump. The head injector provides foamant to be mixed with water inside the pump to create a water-foamant solution. The fire-extinguishing system may also include an inlet mixing valve assembly and an unloader valve to recirculate the water-foamant solution.