Watts 556031 3/4" Lead Free Vacuum Relief Valve is suitable for low pressure steam and water service, and is ideal for use in domestic water heaters and supply tanks. This valve automatically allows air to enter into the piping system to prevent vacuum conditions that could siphon water from the system and damage water equipment. It consists of a lead free brass body construction with NPT male inlet connection, and a protective cap. Maximum working pressure is 200 psi.