Sizing a QF® Duct System

Nordfab offers assistance to those who have never designed a ducting system. We can assist you in determining the correct pipe size and configuration that will supply you with the correct airflow. Our online 3D drawing tool, Quick-Fit Visual® (QFV®) can be used to create 3D designs to help you visualize Nordfab® dust collection duct systems in your facility. QFV provides automatic sizing and static pressure loss calculations. Please let us know if you would like a 3D drawing and estimate for ducting.

Below is an example of system sizing (intended as a guideline only). Dust characteristics, machinery constraints, and other system requirements can affect performance and must be considered.

Skip example and go to  Air Volume Chart

EXAMPLE

Always work from your machines back toward the filter. Suppose that you have a 5" drop that rises and runs back to join with a 6" drop as sketched above. What size branch will you need?

The 5" pipe carries 615 CFM at 4500 FPM, (See chart below). The 6" pipe will need 885 CFM at the same velocity (See chart). Added together you have a total of (615 + 885) 1500 CFM coming together. 

Looking again at the chart under 4500 FPM, you find that 1500 CFM is not listed, but falls very close to the 1570 CFM listed for an 8" pipe. This indicates that the 5" joined to the 6" will require an 8” pipe to carry all of the material at the right velocity. The branch, therefore, will be 8" on the downstream end reducing down to a 5" with a 6" branching off of it. That is listed as an 8-6-5 branch.

Air Volume Chart

USING THE CFM/FPM CHART

This chart allows you to choose the correct pipe size for the CFM that is required.

Different materials need to be conveyed at different velocities to prevent the material from falling out of the air stream. See reference chart

For example, wood chips and saw dust flow well at 4500 feet per minute. Referring to the chart, a 4" pipe will convey 395 CFM at 4500 FPM. This indicates that a 4" pick-up on a machine will use 395 CFM from the filtering system. 

Or working in reverse, if you know that a machine will require approximately 400 CFM to remove the waste, then you should design a 4" pipe for the application.