Opens gradually to admit outside air to relieve a vacuum in a tank. Features iron, steel, or stainless steel body; iron, steel, or stainless steel seat; non-asbestos or TFE disc; size 2" iron with NPT or 125FLG connections, 2" steel and stainless steel with 150 or 300 FLG; 4" through 12" iron with 125FLG, 4" through 12" steel and stainless steel with 150 or 300 FLG. Air relief capacities to 14,280 CFM. Photo: 4" Iron 200. Stainless steel stem and non-asbestos disc assembly, Iron body with seat and brass guide, and stainless steel spring assembly shown separately.