6" vs 5" ducting for Oneida 1.5 HP (internal)

[Anil Kalagatla]

Hi,

I recently bought a (used) Oneida 1.5 HP internal DC (yay!) and ran into this dilemma. Oneida's website recommends 5" ducting for this DC. This has something to do with the FPM becoming too low for 6" ducting (I'm not too sure).

My question is, is it okay to go with 6" ducting for a smallish shop (the ducting will be confined to about 11' X 18' area, with ducts no longer than 15 feet or so).

BTW, do the performance curves published on Oneida's website include the pressure drop due to the Cyclone and the filter? (I hope so)

Thanks! Anil

[JGS]

Hi Anil, I believe the 5" is specified to maintain the required "transport velocity" in the duct. As you go from 5 to 6" the area increases by about

40% therefore the velocity > Hi,

[Anil Kalagatla]

Thanks for your response. Does this depend on the length of the ductwork? Does this mean that the increased CFM due to 6"" is not worth the potential settling of the dust in the ducts? Also, does it make sense to "clean out" the ducts once in a while (not sure how one would go about it).

Anil

[Mark & Juanita]

The transport velocity only depends on duct length to the extent that static pressure drop increases. You want to maintain a minimum of 3500 fpm in mainline ducts and 4000 fpm in branch lines or chips will settle out of the airstream.

You can compute what the velocity in a duct will be using the formula:

Vduct = CFM/A

Where Vduct = velocity of air in duct CFM = Cubic feet per minute A = Area of duct

Area of duct can be computed as: A = Pi * r^2

Where Pi = 3.1415927... r = radius of ductwork (i.e. for 6 inch pipe, r = 3 inches, for

5" r = 2.5 inches)

The answer to your question is that the sizing of the ductwork is a balancing act between volume and velocity. In addition, you want to take into account static pressure drop (one of the reasons 4" ductwork is at a disadvantage). The link contains a very helpful spreadsheet for computing these numbers. Used in conjuntion with a volume vs. static pressure drop curve for your dust collector, you can size your ductwork to provide the capacity you need.