CFM measuring JIG for dust collector?

Is there poor mans CFM meter or a simple JIG one can rig up to estimate the CFM being pulled by a dust collector through a 4 " pipe?
Maybe some sort of calculation based on the deflection of a known size/weight object at the measured opening diameter of the intake? Object might pendulum from top edge of opening.
thanks
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Any jig you can rig up will likely tell you relative CFM, but without a way to calibrate it, you will only be able to tell whether you are drawing more CFM from this port or that. If you use only one port at a time, and ammeter on the line going to your DC may be just as useful as a jig.
--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

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thanks. what is an ammeter?
wrote:

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Given your moniker, I'll point you to this one:
http://www.radioshack.com/product/index.jsp?parentPage=search&summary=summary&cp=&productId !03173&accessoriescessories&kw=ammeter&techSpecs=techSpecs&currentTab=summary&custRatings=custRatings&sr=1&featuresatures&origkw=ammeter&support=support&tabatures
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An ammeter is still not going to give you a flow measurement. It will only tell you how much electrical current your system is pulling.
Air flow can be a tricky science, even to get a relatively low accuracy measurement. Some people spend their entire carrer on just this one area of measurement science. I wouldn't expect to find a simple and cheap way to do it.
You probably will not find an air flow meter for less than around $250 that will give you a readout in CFM and then it won't be a real accurate measurement. Probably in the range of +/- 10% uncertainty.
I thin that a paddlewheel type of anemommeter would be your best bet. They work like a fan in reverse. The air flow turns the fan blades and the speed is measured. This gives an air velocity measurement and the Volume in CFM is calculated by knowing the area of the tube that the meter is installed in.
Since you are probably trying to measure the cfm on you DC you don't want to restrict the line much and that further limits you choices.
There are many methods for air flow measurement, but most of them are pretty complex.
--
Lloyd Baker
"alexy" < snipped-for-privacy@asbry.net> wrote in message
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message wrote:

http://www.radioshack.com/product/index.jsp?parentPage=search&summary=summary&cp=&productId !03173&accessoriescessories&kw=ammeter&techSpecs=techSpecs&currentTab=summary&custRatings=custRatings&sr=1&featuresatures&origkw=ammeter&support=support&tabatures
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I was thinking that the current you drew would be in proportional to the amount of air you move. But others that sound more knowledgable than I said that wouldn't help. And as I think a little about it, it seems that the current you draw (power you use) would depend both on the CFM and the pressure (suction). Sorry for the bum steer.
--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

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trs80 wrote: | Is there poor mans CFM meter or a simple JIG one can rig up to | estimate the CFM being pulled by a dust collector through a 4 " | pipe?
Try a Google group search on alt.solar.thermal for "Air Flow measurements".
Inexpensive _and_ accurate.
-- Morris Dovey DeSoto Solar DeSoto, Iowa USA http://www.iedu.com/DeSoto /
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Thanks for the tip Morris.
I'll have to take a look at that next week some time. I'm off to a living history encampment for the scouts. Portraying the colonial carpenter again, so science thought will be taking a back burner for the next 72 hours.
I am definitely interested in seeing any inexpensive and accurate methods of air flow measurement, but then my definition of accurate may be a little different. Also getting something calibrated, traceable to international standards (a requirement in my line of work), adds cost.
--
Lloyd Baker



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I remember a year or so ago when someone posted here that he'd found a fairly inexpensive wind meter, which he used at the end of the duct to measure the air speed, then used that to calculate CFM moving through the four inch tube.
I don't have time to search for it till later tonight but I remember googling on it then and found that you can get a pretty reasonable figure for your cfm using wind speed and size of duct. The sides of the duct will affect it - smooth sides as in solid sections are better than rough as in flexible tubing, but you can still get a good idea.
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snipped-for-privacy@gmail.com wrote:

Pilot and radio control hobby shops, as well as weather station dealers sell "Kestrel" portable wind meters, like these:
<http://www.weathershack.com/portable-weather-stations.html
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Come to think of it...
If all you want are relative measurements to judge improvement, it seems there is an easy answer.
All you'd need is some sort of DC motor with a fan attached and a digital voltmeter. The motor would probably need to have brushes, I'm not sure if a brushless motor will work as generator. Make a fitting with the fan in it to fit the duct, insert it into the air stream and read the voltage produced. A higher air velocity will produce a higher voltage.
Since the setup is not calibrated to any sort of standard, actual CFM measurements would be impossible. However, the setup would tell you "better or worse" as you make changes.
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trs80 wrote:

Bottom line answer - depending on your definition of "poor" - is probably NO. If about a hundred bucks and some of your time learning about how to use an instrument, how, where and when to take measurements and record them, and what calculations are needed for converting your data to the an answer (ie Feet Per Minute air flow at your measuring instrument, and calculated Cubic Feet Per Minute) is acceptable
THEN
You're in luck.
I just got off the phone with Bill. Hopefully what follows will save him a few more e-mails. Here's the minimum you're going to need to get ACTUAL FPM and CFM in terms of measuring equiptment
Dwyer Model 4010 Magnahelic (about $50-60 US used of eBay or three times that for new from Magnahelich http://www.nciweb.net/capsuhel.htm look for Model 4010
Dwyer 166 pitot tube 6" long (can get to the center of a 12" diameter duct) -eBay running in the $50-60 range, triple that if buying new. http://www.nciweb.net/dwyer_air-velocity_series-160.htm
Combined, these two give you Feet Per Minute - at the point where the end of the pitot tube is located.. If that's at the center of the duct you're getting the Max speed in the round duct. Because the air is moving slower the closer you get to the walls of the duct (friction starts slowing the air flow down), a rough estimate of average speed is Max Speed x 0.90.
With the Average Feet Per Minute speed and the cross sectional area of the inside of the duct you can calculate the Cubic Feet Per Minute (CFM) by multiplying the Average FPM x the Cross Sectional Area of the inside of the duct (in Square Feet, not square inches).
Note: getting the pitot tube aligned right and postioned in the center of the duct is up to you. The instruments will measure a pressure differential. You have to make sure you put it where you want it to be.
Now as to hand held plastic"wind meters" - the little things with the plastic fan blade. They're intended to measure wind speeds you can stand in - not hurricane speeds. In a dust collector you're looking for 3700 to 3800 feet per minute, AT A MINIMUM, air speed. http://BillPentz.com/woodworking/cyclone/DC4Dummies.cfm#Airspeed
That's around 42 to 43 MPH. On larger dust collectors you might get air speeds well above that depending on where you're measuring. Above 70 mph the plastic hand held may fail / come apart. Then there's the affect of the body of the unit and your hand holding it - in a relatively small opening - vs over your head while standing on the beach or mountain top - in the middle of a hurricane (on the leading edge or trailing edge, not in the "eye") Turbulence in the air stream being measure raises all kinds of hell in air flow.
For more on the basics read, and understand the FAQ on Bill's site.
http://BillPentz.com/woodworking/cyclone/FAQs.cfm
And PLEASE - don't e-mail him for a while - he's got his hands really full right now.
Hope this helps.
charlie b
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great input. thanks

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If I make my own slack tube Manometer, do both ends of the manometer have to be the same opening diameter? Could I put a npt in the outside the duct connected to plastic slack tube with a metal tube inside and the metal tube opening being smaller then the opening at the other end of the plastic tube? Then measure water column difference to calculate the cfm? thanks again

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A plastic garbage bag. Time how long it takes to fill up.
Wind velocity is one thing you can sense, but until you understand the way that velocity is mapped to the full surface area of the pipe, it isn't enough.
Back pressure is another thing you can sense, and if your pipe is long enough (to get away from turbulence at the ends) a U-tube manometer with some water in it can be attached to the pipe at two points in the flow, and the resulting pressure measurement (like, "in two feet of 4" pipe, there was 25mm of water pressure drop") will be roughly proportional to the square of the flow rate.
You can use such a U-tube and calibrate with the plastic bag and get some idea when your filters are clogged (and stopping the flow). You can also use a U-tube (or any other) manometer for sensing the backpressure from the filter inlet and outlet and this also tells you when the filters are clogged, but isn't sensitive to inlet port choking. In filter rooms I'm familiar with, this measurement (the backpressure across the filter) is the important indicator of performance.
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