... 1.Positive voltage air duct 2.specification:dia 300,400,500,600,800,1000 Positive voltage air ductPurpose: Fan machine could used it ... in coal mines, tunnel, underground for positive pressure ventilation Air duct structure and dimension ... . 3-fling ring 4-reverseItemDimensionTolerance(mm) Diameter of air duct(mm)300 400 450 500 600 800 10000~±6Length of ...