Dust collector duct balancing

[Bill LaPointe]

Am finishing re-ducting my dust collector. 3 HP Jet. Thein Baffle. 6" PVC duct. Most ports have 6" hoods or dual 4" to the machine. My small BS and my SMS both have 2 1/2" ports fed by the same 6" blast gate at the end of a 6" main duct, 30' from DC. Should I partially open another blast gate in the system to compensate for the reduced area of the small ports when in use? How do I determine how much to open the other gate? Amp meter, static pressure gauge? Any help appreciated.

[Dan Friedrichs]

No, I wouldn't. The only concern would be that you don't have enough volume of air moving to keep the dust from settling in a horizontal run of pipe. I can't imagine how you would actually run into any trouble with tools like your BS and MS that don't produce that much dust. In any case, as soon as you open a large blast gate, it should sweep away anything that settled.

[Rod Sheridan]

I always open another port when using low volume devices, both to keep the dust entrained and to allow enough air flow for separation in the cyclone.

Without enough velocity in the cyclone, all the dust goes into the filters.

I expect that a Thien separator would have the same problem with very little airflow.

Regards, Rod.

[Cliff Holmes]

On the bandsaw, you could create multiple lines to grab all the dust. See the bandsaw section of my dust collection page (http://www.thewoodnerd.com/workshop/dustCollection.html#bandsaw) for how I did mine.

For a miter saw, a hood is the only really effective method, that little blade shroud port isn't all the great. The one I built (http://www.thewoodnerd.com/workshop/mitersaw.html) is very effective, it'll pull fine dust from several feet away.

[Dan Friedrichs]

Without enough velocity in the cyclone, all the dust goes into the filters.

I expect that a Thien separator would have the same problem with very little airflow.



I'm not sure you need high airflow to keep the separation happening with a Thien baffle. Perhaps Phil can tell us...

[Jim Andrew]

Tools with small dust ports I use a shop vac to collect dust. Doesn't seem like my dust collector works well on small openings.

[Stephen Cherry]

How do I determine how much to open the other gate? Amp meter, static pressure gauge? Any help appreciated.

It's possible to measure airflow through the duct using what's called a "pitot tube". It's an arrangement of tubes, usually small in diameter, where one tube points into the wind, and the other is at a 90 degree angle to the flow direction. The difference in pressure is related to flow velocity. to measure the pressure difference, you can use something like aquarium tube formed into a downward facing loop, with water in the bottom of the loop:

http://en.wikipedia.org/wiki/File:Utube.PNG

Or you could use a gauge like the dual scale air velocity magnahelic:

http://www.dwyer-inst.com/PDF_files/Priced/2000_cat.pdf