FEBCO 600PVB Lead Free Pressure Vacuum Breaker - This lead free freeze-resistant pressure vacuum breaker backflow preventer is designed to prevent backsiphonage of contaminated water under continuous pressure into the potable water supply. Its superior design protects the valve body and internal components during sudden freeze conditions. Water inside the PVB freezes from the outside-inward. As the ice forms and expands causing a buildup of pressure, the breaker relieves the pressure through a unique relief valve built into the plastic float. Test cocks are positioned at the lowest point of the valve for winterization draining.