Diagram the calculation method of duct quantities

In the calculation of air duct quantities: air ducts of various materials and shapes are calculated by the expanded area (m²) of different specifications in the construction drawing, without deducting the area occupied by inspection holes, measuring holes, air supply outlets, air suction outlets, etc. The length of the air duct shall be subject to the length of the centerline on the construction drawing, including the length of elbows, tees, reducers, and other pipe fittings, but shall not include the length of components. The diameter and perimeter shall be developed according to the dimensions shown in the drawing. The overlapping part of the snap has been included in the quota and shall not be calculated separately.
When calculating the length of the air duct, the length of the position occupied by the components (air duct valve, air outlet, hood, hood, air pressure box, muffler, etc.) shall be subtracted. The length of some ventilation components is as follows:
Butterfly valve: L=150mm.

• Check valve: L=300mm.
• Closed split multi blade regulating valve: L=210mm.
• Round air duct fire damper: L=air duct diameter D+240mm.
• Rectangular air duct fire damper: L=air duct height B+240mm.

The main pipe and branch pipe of the ventilation pipe are divided from the intersection of the center line to determine the length of the center line, as shown in the following figure:

General knowledge of duct engineering:
Fabrication of air duct: setting out, blanking, rolling, square folding, rolling, seaming, fabrication of straight pipe, pipe fitting, flanges, hanger brackets, drilling, riveting, upper flange, assembly.
Installation of air duct: elevation finding, support wall opening, matching with reserved holes, embedding bracket, assembly, air duct in place, leveling, alignment, cushion making, cushion, bolt mounting, fastening.