Series 7001, 7002 UL/FM Fire Service Strainer is used in conjunction with a water spray system to protect the system against clogging that can be caused by particles fouling the small discharge opening of the sprinkler heads. Strainers for fire systems are designed to trap foreign material 1/4" diameter or larger. This type of strainer is usually installed upstream of most of the devices in the system including the meters, backflow preventers (or detector check valves) and flow alarms, in order to protect these devices from damage caused by large particles.