The Colt LFC300, LFC300N Double Check Detector Assemblies are used to prevent backflow of pollutants, that are objectionable but not toxic, from entering the potable water supply system. The Colt LFC300, LFC300N may be installed under continuous pressure service and may be subjected to backpressure. The Colt LFC300, LFC300N is used primarily on fire line sprinkler systems when it is necessary to monitor unauthorized use of water. For use in non-health hazard applications.