A duct is a system of ducts used for air transport and distribution. Ducts can be classified by section shape and material. According to the cross-sectional shape, air ducts can be divided into circular air ducts, rectangular air ducts, oblate air ducts, etc.Among them, the circular air duct has the smallest height and the largest size and is complicated to manufacture. Therefore, the application is mainly based on rectangular ducts. According to the material, air ducts can be divided into metal air ducts, composite air ducts, sos air ducts, etc.
Installation of air duct system: flexible short pipes should meet the following requirements: materials that are anti-corrosion, moisture-proof, airtight, and not easy to mildew should be selected. It should also be used to purify the air-conditioning system with a smooth inner wall and not easy to generate dust. The length of the flexible short tube is generally 150 to 300 mm. When the air duct passes through the fireproof and explosion-proof wall or floor that needs to be closed, a pre-buried pipe or protective casing should be installed, and the thickness of the steel plate should not be less than 1.6mm.
Between the air duct and the protective casing, there should be non-combustible and non-hazardous flexible materials to block the human body. The installation direction and position of fire dampers and smoke exhaust valves (ports) should be accurate. The fire dampers on both sides of the partition wall of the fire compartment should not be greater than 200mm from the wall surface.

1. The air duct is installed horizontally, the side length is less than or equal to 400mm, and the spacing should not be greater than 4m; if it is greater than 400mm, it should not be greater than 3m; for the duct with thin steel flange, the spacing between its supports and hangers should not be greater than 3m.
2. The air duct should be installed vertically, the spacing should not be greater than 4m, and a single straight pipe should have at least 2 fixed points.
3. The support and hanger should not be set at the tuyere, valve, inspection door and automatic control mechanism, and the distance from the tuyere or plug pipe should not be less than 200mm.
4. When the length of the horizontally suspended main and dry air ducts exceeds 20m, a fixed point to prevent swinging should be set, and each system should not be less than one.
5. When the diameter or length of the fire damper is greater than or equal to 630mm, independent supports and hangers should be provided.
6. The air outlet with high-efficiency filter should adopt a boom that can be separated and adjusted in height.

Reinforcement of metal air ducts: the side length of the rectangular air duct is greater than 630mm, and the side length of the thermal insulation air duct is greater than 800mm. And the length of the pipe section is greater than 1250mm or the unilateral flat area of the low-pressure air duct is greater than 1.2m2, and the medium and high-pressure air ducts are greater than 1.0m2, and reinforcement methods should be adopted. For the reinforcement of angle steel and reinforcing bars, the height should be less than or equal to the width of the air duct. The interval between angle steel, reinforcing bar and air duct riveting should be uniform and should not be greater than 220mm. For the purification air conditioning system, the reinforcement frame and reinforcement bars should not be set in the air duct..