Dust Collection Duct Velocity Calculator
Determine required particulate conveying transport velocity (FPM), round duct diameter (inches), actual flow velocity, and velocity pressure according to ACGIH standards.
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Industrial Ventilation Ductwork Conveying Velocities (ACGIH)
In dust collection exhaust ventilation, air does not merely ventilate a hood; it must physically convey solid particulate matter through horizontal ducts without allowing particles to drop out of suspension. If air velocity drops below the critical saltation threshold, dust settles on the bottom of the duct, creating combustible fire/explosion hazards and restricting airflow.
ACGIH Recommended Minimum Transport Velocities
- Vapors, gases, smoke: 1,000 – 2,000 FPM (no settling concerns).
- Very fine light dusts (lint, flour, wood flour): 2,500 – 3,000 FPM.
- Standard dry industrial dusts (wood shavings, grain, plastics): 3,500 – 4,000 FPM.
- Heavy or abrasive dusts (cement, sand, metal grindings): 4,000 – 4,500 FPM.
- Heavy moist or dense dusts (lead dust, wet foundry): 4,500+ FPM.
Velocity Pressure Formulation
VP (inches water gauge) = [ Velocity (FPM) / 4005 ]²
Frequently Asked Questions
Why is transport velocity so important in dust collection ducts?
Unlike HVAC ducts where air speed is minimized to reduce noise, dust collection ducts must maintain high air velocity (3,500 to 4,500 FPM) to prevent dust from settling, plugging ducts, and causing combustible dust explosion hazards.
What is the formula for velocity pressure (VP)?
Velocity pressure in inches of water gauge is calculated as VP = (Velocity in FPM / 4005)². At 4,000 FPM, the velocity pressure is exactly 1.00 inch w.g.
Why are round ducts preferred over rectangular ducts in dust collection?
Round ducts have no dead corners where dust can settle, provide uniform velocity profiles, and better withstand high negative static pressure without collapsing.