Air conductors of circular cross-section (round air conductors)
Air conductors of circular cross-section, through which air with a temperature below 80 ° C is transported, should be made of steel sheet thickness, not more than:
– round air conductors with a diameter of less than 250 mm – 0.5 mm;
– round air conductors with a diameter of 250 to 450 mm – 0.6 mm;
– round air conductors with a diameter of 500 to 800 mm – 0.7 mm;
– round air conductors with a diameter of 900 to 1250 mm – 1.0 mm;
– round air conductors with a diameter of more than 1250 mm – 1.2 mm;
The air conductor network should be assembled from standardized fittings (straight sections, branches, transitions, tees, tie-ins, crosses and plugs) of appropriate diameters.
Air conductors of circular cross-section can be spiral-wound, straight seam, flanged and flexible.
Spiral coiled air conductors have become increasingly popular in recent years due to their low manufacturing costs.
Spiral coiled air conductors are made of galvanized steel strip with a thickness of 0.55 and 0.7 mm in a fully automated cycle. Their length can be from 1 to 6 m. Spiral coiled air conductors are connected to each other using internal or external nipples. In addition, a wide range of fittings is available for them. These include central and one-way transitions, 15, 30, 45, 60 and 90° bends, straight and angled tees, crosses, inserts, plugs and umbrellas. When installing the conductors, the connecting sections of the fittings are inserted into the conductors, and the joints are automatically sealed.
Somewhat less commonly, but still used, are longitudinal round air conductors. Straight-section circular air conductors are made of galvanized steel sheet with a thickness of 0.5 – 0.7 mm so that during installation the end of one conductor is included in the beginning of another. Due to the high cost of manufacturing, longitudinal circular air conductors are used in ventilation systems of short lengths or with certain technological requirements.
In ventilation systems with large diameters and wall thicknesses, where periodic disassembly is required, as well as in aspiration systems, round air conductors with flanged connections are used. The flanges are made of a corner bent to a certain diameter and welded at the joint, and are stuffed onto the conductors. Sealing of joints between air conductors is carried out with the help of rubber or felt gaskets installed between two adjacent flanges, bolted together.
Nowadays, flexible air conductors have gained great popularity in the installation of not very large ventilation systems. Flexible air conductors are made of aluminum-polymer sleeves reinforced with steel wire or corrugated aluminum sheet. Insulated (insulated) flexible air conductors with an outer layer of synthetic winterizer are used in ducted air conditioning systems and supply ventilation systems. Flexible air conductors should not be used on long (more than 4 m) sections due to significant aerodynamic resistance. However, in combination with steel rigid air conductors, flexible air conductors are widely used. The standard sizes of flexible air conductors are also unified:
100 – 4“; 125 – 5”; 150 – 6“; 200 – 8”; 250 – 10“; 315 – 12”; 355 – 14”
Flexible air conductors of larger diameters are also offered by some manufacturers, but they are rarely used.
It should be noted that for special ventilation systems, aspiration systems, and for various technological processes, flexible air conductors made of polymeric materials reinforced with steel wire are also used. The diameters and materials from which such flexible air conductors are made are represented by a wide range, but they are used mainly in special industries.