Stainless Steel Reduced Pressure Backflow Zone Assembly with OS&Y and Flood Sensor. Series 4000SS provides protection of the potable water supply in accordance with national codes. This series can be used where approved by the local authority having jurisdiction on health-hazard cross-connections. Series 4000SS features short lay length, light weight stainless steel body, corrosive resistant stainless steel relief valve, and patented cam-check assembly. Series 4000SS includes a flood sensor to detect excessive water discharges from the relief valve. The sensor is installed on the assembly exterior and does not alter assembly functions or certifications. The sensor relays a signal that triggers notification to facility personnel for corrective action, thus limiting flooding and costly damage.