Marketing InformationSeries AS air separator is designed for efficient separation of air from water in hydronic heating systems. WATTS® air separators have heavy cast-iron construction. They have tappings for the installation of an expansion tank and air vent. Entrapped air-in the hot water heating system piping is dispersed by the internal agitator of the air separator as the water is recirculated within the heating system piping. This provides quiet efficient operation of the hot water heating system radiation.