Dust Collector Duct Sizing

Where to look for info on proper ductwork diameters. May 16, 2005

I just purchased a 5hp, 4 bag collector with an 8" intake and a 13.1/2" impeller diameter. I need to run about 30 feet of trunk line to drop to most of my machines. The stated useful volume airflow is 2514 cfm and the "collector inlet vacuum~in.H2O" is 5. What would be the right size trunk line in this setup? My table saw needs 1100 cfm.

Forum Responses
(Dust Collection Forum)
From contributor B:
Go to the company you are going to buy the duct from. Give them a drawing of the layout and they will draw the trunk and drops needed to supply the machines. They have a program that does this for them. We did it on our current system and it works great.

From the original questioner:
This is a Woodteck Machine from Woodworkers Supply - same machine as all the other Taiwanese built collectors. Just wondering what other shops have done to get the most suck for the buck on their bag over bag machines.

From contributor O:
Are you using an over-arm blade cover? If you are, you may want to use 8" mains, along with a 7" or 8" drop to the saw, splitting to a 6" to the base, and a 4" to the over-arm blade cover.

This should easily flow well over 800 cfm to the base, with reasonable static pressure losses, and about 400 cfm to the over-arm blade cover, depending on its internal porting. The smallest internal diameter there will determine the flow.

Velocity in the main should be well above desired flow minimums. Velocity in the 7" drop would easily exceed 4000 fpm (closer to 4500 fpm).

These numbers presume that the actual performance of your dc is as stated, and whether or not you're using blast gates for the different drops, as well as the size of those other drops.