Air ducts are designed to transport air of the ventilation system.
OS3-d (spiral) made out of galvanized band steel, L-3000 mm. When air duct is manufactured are designed to be outside the duct, in this way vortexes are avoided to form inside the ducts. Furthermore, due to this design, air flow loss is reduced to minimum. Medium and higher diameter range ducts are harden with two small low angle pressed curvatures.