ZENNER FHZD Hydrant Backflow Meters, with built-in dual check valves and RPZ dump valve, are designed to measure a wide variety of cold potable water flows from fire hydrants where flows are in one direction. These meters are light weight portable units designed for temporary installations. The built-in dual check valves help provide a practical solution to help prevent backflow into the primary water source. The RPZ (Reduced Pressure Zone) Dump Valve allows this assembly to dump to atmosphere when the check valves are fouled.