Gorton, No. D, 1/8" Straight Vapor Equalizing, Steam Air Vent Valve, #D 1/8" 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.