# Shop Measurements: Dust collector air velocity and flow rates

• posted on November 28, 2004, 7:06 pm
All the books about dust collectors stress having ducts with sufficient air velocity to keep the wood particles in suspension to avoid blockages. This means the duct should not be "too large." Sandor Nagyszalanczy, in "Woodshop Dust Control" quotes 3500 FPM as optimum. On the other hand, duct with too small a diameter will decrease air flow thereby reducing collection efficiency because of pressure drops across the ductwork. He quotes 350 -500 CFM flow rates at each machine for adequate dust control.
Having just bought a used Penn State DC1B dust collector I was interested in measuring FPM and CFM values so I could size my duct appropriately. A Google search for anemometers showed mostly \$200 and up units, which would be a no-go for me. However I found a newly released unit for about \$40.00-\$50.00 designed for wind speed measurements. It's a Lacrosse EA-3010U, on Amazon at http://tinyurl.com/4s5f2 . The Lacrosse link is http://www.lacrosse-htawi.com/ea-3010u.html . It's a tiny thing, about 1" x 4". It can be set to measure wind speeds up to 67 mph, and can be set to read out in meters per second, m/s. Actually it also measures temperatures and wind chills for you weather fans. (BTW, I have no relationship with the Lacrosse folks.)
Knowing how much I have spent and will spend on DC equipment I figured \$40. was worth it to get some quantitative measurements, so I bought one. (Plus, like many WW'ers I love gadgets.)
Here are the formulas for FPM and CFM starting with air velocity in m/s and duct diameter in inches:
Air velocity in FPM = m/s * 197.
Air flow in CFM = m/s * (duct diameter in inches)^2 * 1.05.
My DC1B showed an air velocity of 6107 FPM at the DC with one 4" port open and no load, decreasing to 3940 FPM with both 4" ports open.
The air flow was 672 CFM with both ports open, decresing to 521 CFM with only one port open. Penn State advertises about 875 FPM for the new DC1B-XL model that superseded my DC1B, so my machine is about in line with what I would expect.
Now to measure the air flow with duct in place, which will no doubt be depressing.
--
Vince Heuring To email, remove the Vince.

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• posted on November 29, 2004, 6:10 am

How about replacing the dual 4" ports with one 6" port? That's possible on my Jet DC1200 and probably on yours as well. Several people have run 6" pipe for their system and are very satisfied with it. Are you acquainted with Bill Pence's website on dust control? He has a spreadsheet for doing the calculations that is very practical to use. By the way, I think, in general, you need 2 hp or more with a 12" impellor to support a 6" system.
Bob
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• posted on November 29, 2004, 5:35 pm
On Mon, 29 Nov 2004 06:10:41 GMT, "Bob"
|
| | |> My DC1B showed an air velocity of 6107 FPM at the DC with one 4" port |> open and no load, decreasing to 3940 FPM with both 4" ports open. |> |> The air flow was 672 CFM with both ports open, decresing to 521 CFM |> with only one port open. Penn State advertises about 875 FPM for the |> new DC1B-XL model that superseded my DC1B, so my machine is about in |> line with what I would expect. | |How about replacing the dual 4" ports with one 6" port? That's possible on |my Jet DC1200 and probably on yours as well. Several people have run 6" |pipe for their system and are very satisfied with it. Are you acquainted |with Bill Pence's website on dust control? He has a spreadsheet for doing |the calculations that is very practical to use. By the way, I think, in |general, you need 2 hp or more with a 12" impellor to support a 6" system.
It's Bill Pentz. http://billpentz.com/
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• posted on November 29, 2004, 11:35 pm

So do you think you wasted your money or not....on the anemometer?
I have 2 dust collectors and I really do not mind "wasting" lol 30 bucks if the anemometer will give me some correct answers... has to be more accurate then just sticking my hand in fron of a blastgate and judging air flow... which has been my method of choice for the last 10-15 years since I installed my first DC.... actually I am more interested in seeing just how much a cyclone trash can lid effects the machine...My system looses a lot of "suction" when I hook up the cyclone using my method..
Bob Griffiths
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• posted on November 30, 2004, 9:06 pm
No way, for the reason you stated below: data on duct sizing and when I need a bigger DC. :-)

Yup, bad math. The two figures were 20 and 31 m/s. You're right in general, though. 31 m/s is just at the maximum measurable wind speed with this model.
Regards, Vince
--
Vince Heuring To email, remove the Vince.

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• posted on December 1, 2004, 4:27 pm
On Tue, 30 Nov 2004 14:06:50 -0700, Vince Heuring

Thanks Vince....my wallet will be 30 bucks lighter very shortly...
Bob Griffiths
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• posted on November 30, 2004, 3:44 am
wrote in

This sounds great, Vince. But I think maybe I'm doing the math wrong. Near as I can figure, you're getting 30 or 40 m/s for those numbers, and that works out to more than the meter's capacity of 67 mph.
By the way, did you know if you type "40m/s in mph", without the quotes, into the google search box, it'll convert it to mph?
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• posted on November 30, 2004, 3:58 am

COOL!
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• posted on November 30, 2004, 4:00 am
Dan wrote:

You probably know this, but for the edification of others, it'll do this for just about anything. I was going to calculate the size of a resistor I'd need recently, and suddenly thought, "Hey, I wonder if Google could do this?" I "searched" for "9 volts / 45 milliamps" (or somesuch, don't remember the real exact numbers) and it said, "200 Ohms." I was quite impressed. I do wish they documented that thing better, tho. I'm sure there are all sorts of cool things it does that nobody's noticed, yet.
ObRW: It doesn't do anything useful with "12x6x32 inches in board feet" though. :(
-BAT
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• posted on November 30, 2004, 4:46 am

Or currency. :-) I guess they don't feel like keeping the dollar value updated.
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• posted on December 7, 2004, 3:02 pm
wrote:

Amazon is currently showing the device as out of stock and a price of \$39.99. Another source (\$5.00 cheaper and free shipping) is:
http://www.clorders.com/lacrossespecialty.htm
The same page has a device that looks like it might serve as a remote control switch for a DC or other appliance. Didn't check the specs, so don't know for sure.
Standard disclaimers apply.
Tom Veatch Wichita, KS USA
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