Embodiments of the invention provide a fire-extinguishing system for injecting foamant into a stream of water. The system can include a flow meter determining a flow rate of the stream of water and a foam pump having an inlet coupled to a supply of foamant and an outlet coupled to the stream of water. The system includes a servo motor driving the foam pump. The servo motor includes a sensor used to determine a rotor shaft speed and/or a rotor shaft torque. A controller can control an operating speed of the servo motor using closed-loop control depending on the flow rate and the rotor shaft speed and/or the rotor shaft torque.