Gorton, No. D, 1/4" Straight Vapor Equalizing, Steam Air Vent Valve, #D 1/4" air vent INSTALL where a large amount of air must be vented. (NOT TO BE USED ON HAND FIRED SYSTEMS UNLESS RADIATOR SUPPLY VALVES ARE LEFT ON ALL THE TIME. ) 1/8" connection, VENTING CAPACITY... Equal to 27 ordinary type air valves.