Technical calculation · Duct line
Dust collection duct calculation.
Calculate the duct diameter for the conveying velocity, the duct pressure loss and the approximate total pressure required from the fan.
3D view
Air speeds up as the duct narrows
At constant airflow, velocity rises as the cross-section shrinks (Q = A × v). The diameter you calculated is shown side by side with one size larger and one size smaller: in the wide section the velocity drops below the conveying velocity and dust settles; in the narrow section velocity and friction loss increase.
Preparing the 3D view…
The illustration explains the preliminary calculation; it is not to scale. The view changes as you change the values.
Calculation method
How is a dust collection duct calculated?
The duct diameter is governed by the minimum velocity needed to carry the dust without it settling in the duct. Dividing the airflow by this velocity gives the duct cross-section, and a standard diameter that does not reduce the velocity is selected. The pressure loss is the sum of the friction in the straight duct and the hood entry, elbow and discharge losses. Adding the loss of equipment such as a filter gives the total pressure of the fan.
Worked example
10,000 m³/h of general industrial dust, 18 m/s conveying velocity, 30 m of duct, 4 elbows and 1,500 Pa filter loss:
Diameter: theoretical ≈ 443 mm → Ø450 mm standard duct, velocity ≈ 17.5 m/s
Duct loss: friction ≈ 202 Pa + local losses ≈ 494 Pa ≈ 696 Pa
Fan total pressure: (696 + 1,500) × 1.10 ≈ 2,420 Pa (246 mmH₂O)
| Conveyed material | m/s |
|---|---|
| Smoke, vapour, welding fume | 12 |
| Light fine dust (flour, textile, sanding dust) | 15 |
| General industrial dust (grinding, cement, ceramics, grain) | 18 |
| Heavy dust and chips (wood chips, metal swarf, sand) | 21 |
| Moist or sticky heavy dust | 24 |
For long horizontal runs and moist dust, the next higher value is preferred.
Points to watch
Common mistakes in duct lines
- Do not let the velocity drop. If the duct is oversized, dust settles in it and the line blocks.
- Size each branch separately. In multi-point systems every extraction point is calculated for its own airflow and the line is balanced.
- Use long-radius elbows. The elbow radius should be at least 2D, and branches should join the main duct at an angle of 30–45°.
- Reinforce elbows for abrasive dust. With sand, slag and metal dust, heavy-gauge sheet or wear plates are used at the elbows.
Leave the calculation to our engineers.
Send us your airflow, dust type and plant layout; we will size the fan, filter and duct line together and prepare your quotation.