Watts® LFN36-M1-1/2 Lead Free Water Service Vacuum Relief Valve, 1/2"Used in water heater tank applications to automatically allow air to enter into the piping system to prevent vacuum conditions that could siphon the water from the system and damage water heater tank equipment. It consists of a lead free brass body construction with npt male inlet connection, and a protective cap. 1 2" Lead free Allows air to enter a closed system to automatically relieve vacuum conditions which could siphon the water from the system,