Watts 8 1 2 in x 5 1 4 in Boiler Feed Valve w Backflow Preventer, FNPT x Sweat Union B911S M3 Nominal Size 52" X 1.5" These products clean away dirt These products clean away dirt and grime and eliminate germs and other disease causing microscopic organisms to stop them from spreading The gray lid is secured to the wall bracket with a lock and removable key to help prevent both theft and tampering Model provides make up water to the boiler and can prevent backflow when the supply pressure falls below the system pressure this WATTS boiler feed valve with backflow preventer is for use in residential and commercial hydronic heating systems