Air ducts of a circular cut, in which the air is moving at a temperature below 80°C, must be made of sheet steel of a thickness of not more than:
– round air ducts with a diameter less than 250 mm – 0,5 mm;
– round air ducts in diameter from 250 to 450 mm – 0,6 mm;
– round air ducts in diameter from 500 to 800 mm – 0,7 mm;
– round air ducts in diameter from 900 to 1250 mm – 1,0 mm;
– round air ducts with a diameter more than 1250 mm – 1,2 mm;
The network of air ducts should be made up of shaped products (straight sections, bends , transitions, tees, inserts, crosspieces and plugs) of the appropriate diameters.
The air ducts of the circular cut are spiral-swirling, straight-line, flange and flexible.
Recently, due to the low cost of manufacturing increasingly widespread use of spirally wound air ducts. Spirally wound air ducts are made of galvanized steel tape of thickness 0,55 and 0,7 mm in fully automated cycle. Their length can be from 1 to 6 m. Spirally wound air ducts are interconnected by means of internal or external nipples. In addition, a wide range of shaped parts are made for them. These are central and one-way transitions, bends at 15°, 30°, 45°, 60° and 90°, straight and angle tees, crosspieces, inserts, plugs and exhaust umbrellas. When installing the channels, the connecting sections of the shaped parts are inside the air ducts, at the same time there is an automatic sealing of the joints.
Somewhat rarer, but still using straight round air ducts. The straight air ducts of a circular cut made of sheet galvanized steel with a thickness of 0.5 – 0.7 mm are made in such a way that, at installation, the end of one air duct enters the beginning of another. Because of the high production cost, straight round air ducts are used in vent systems of small length or with certain technological requirements.
In vent systems with large diameters and wall thickness of air ducts, where they need their periodic disassembly, as well as in systems of aspiration, round air ducts with flange connection are used. The flanges are made from an angle, bent under a certain diameter and welded at the junction, and put on on the air duct. Sealing of joints between air ducts is carried out by means of rubber or felt pads, which are installed between two adjacent flanges, tightened by bolts.
In our time, great popularity in the installation of not very large ventilation systems have gotten flexible air duct. Flexible air ducts are made of aluminum-polymer sleeve, reinforced with steel wire or corrugated aluminum sheet.In channel air conditioning systems and inflow ventilation systems, insulated (warmed) flexible ducts are used, with an outer layer of synthetic heater. The use of flexible ducts on long (more than 4m) sites is not worth due to significant aerodynamic resistance. But in the combination with steel rigid air ducts, flexible ducts get quite wide application. Dimensions of flexible ducts are also standardized:
100 – 4″; 125 – 5″; 150 – 6″; 200 – 8″; 250 – 10″; 315 – 12″; 355 – 14″
Flexible ducts of larger diameters are also offered by some manufacturers, but they are extremely rarely used.
It should be noted that for special systems of ventilation, systems of aspiration, for various technological processes also flexible air ducts from polymeric materials, reinforced with a steel wire are used. The diameters and the material from which such flexible air ducts are made present a large assortment, but are mainly used on special manufactures.
Throttle valves for round ventilation ducts
The throttle valve is designed for operation in the air supply systems. When the valve is closed, about 10% of the channel remains open. The throttle shut-off round valve can work by adjusting the air flow in any quantity, and completely block the air flow.
The throttle valves are made of galvanized steel, the axis of rotation – in the polyamide bushings. Maximum operating temperature +50°С. Their main advantages are: small length, high rigidity and high tightness of connection to air ducts (on both ends there are grooves with T-shaped rubber sealing – option).
The throttle shut-off round valve can also be used with electric drive. Preferred set position can be fixed with a “nut-butt”.
Noise-absorbers for round ventilation ducts
Round noise-absorbing D 00-L
D — nominal diameter, mm;
00 — code (00 – D (diameter));
L — length of noise absorber.