The ratio controller accurately proportions foam concentrate into a water stream over a wide range of water flow rates. Ratio controllers are an integral part of an approved foam system. In addition to the ratio controller, the main components of the approved foam system are specific foam concentrates, a foam storage tank, a concentrate control valve and foam discharge devices. The system must be designed so that the ratio controller can accurately proportion foam over the range of flow rates expected during the system operation. Intended for use in Wet, Dry, Deluge, Preaction and Refrigerated Area applications.