Sizing Ductwork for Dust Collection Systems

Ductwork is used to carry the dirt and air from the collection point to the collector. It must be sized properly to create a “carrying velocity” to keep dirt moving through. Duct sizing is based on 2 variables: the particulate being collected and the volume of air being moved. The heavier the dirt, the higher the air velocity needed.

Example

Steel grinding dust conveyed @ 3500 feet per minute (velocity). A typical grinder uses 500 cubic feet of air per minute (cfm) to control dust. To move this much air, select an appropriate size of ductwork – in this example, a 5-inch diameter duct yields just over 3500 feet per minute for 500 cfm air volume.

If the ductwork is too small, two problems can occur:

• Higher pressure loss (delta P) and higher energy usage because of higher velocity.
• Increase delta P will reduce air volume entering the collection hood, degrading the performance of the dust collector.

If the ductwork is too large, two problems may happen:

• If the volume of air is not increased, dirt will not be carried through the ductwork and material will collect inside.
• If the particulate is heavy, the ductwork will become heavier than the structure support can carry and may crash to the floor. 

Bottom line

Correct sizing of the ductwork is a key factor in the dust collection system.​