CFM Requirements For Duct Collectors
Many dust collection systems are used for typical shop equipment such as lathes, joiners, table saws and routing tools. Most dust collectors are rated in FPM (feet per minute), with 4,500 FPM required to remove the dust from two to four appliances at one time, but no more than four. The CFM (cubic feet per minute) calculation is for the exhaust portion of the system. The CFM requirements differ per the equipment being exhausted and the diameter of the pipe. The exhaust system controls the vacuum pressure within the dust collection system. The dust collection system must have an air exhaust to pull some of the air in the system out of the building to control duct static pressure. The collected material drops into the dust collector from the collector pipes and the excess air is released through the exhauset port. The following table shows the CFM per pipe diameter required to maintain proper air flow through the system.
CFM for for pipe diameter at a specified velocity
Diameter 3500 FPM 4000 FPM 4500 FPM
3" 277 316 356
4" 305 348 392
5" 477 546 614
6" 686 784 882
7" 935 1,068 1,202
8" 1,222 1,396 1,570
9" 1,546 1,767 1,988
10" 1,909 2,182 2,455
12" 2,749 3,142 3,534
14" 3,742 4,276 4,810
Location of Equipment
For optimal dust collection, the system should be set up so that all tools that are on the system are set up in a circular pattern. This minimizes severe bends that cause clogged pipes and static pressure issues within the dust-collection system. It also sets up a user-friendly flow in a shop so that every piece of equipment has its place.
Dust Collection System Piping
The piping commonly used in dust collection systems is PVC and spiral metal. Spiral metal is more expensive, but is made especially for ductwork systems like dust collectors that allow the air to move naturally down the lines without building up static electricity. PVC piping does work for dust collection but builds up a tremendous amount of static electricity. This can be a shock hazard and could possibly ignite fine dust particles. Professional dust collection system installers only use metal spiral ducting for this reason.