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Measuring CFM

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Forum topic by trevor7428 posted 09-06-2016 03:48 PM 526 views 0 times favorited 13 replies Add to Favorites Watch
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trevor7428

149 posts in 425 days


09-06-2016 03:48 PM

What is a reliable tool to measure CFM for my dust collector without breaking the bank?

I found This and This on Amazon.

Does anyone have any experience with these cheep Anemometers? I don’t want to spend hundreds of $ to test out my dust collection. I am really hoping one of these will work for my needs

-- Thank You Trevor OBrion


13 replies so far

View Andre's profile

Andre

1022 posts in 1271 days


#1 posted 09-06-2016 04:12 PM

The first one looks like one I bought from Auckland’s for $200. Works great if you follow instructions. I input the sq/in factor for different duct size, use mine in the house to check air return flow to furnace.

-- Lifting one end of the plank.

View RobS888's profile

RobS888

1986 posts in 1310 days


#2 posted 09-06-2016 05:05 PM

I returned the single piece unit and got the Pyle, I’m very happy with it.

-- I always suspected many gun nuts were afraid of something, just never thought popcorn was on the list.

View AZWoody's profile

AZWoody

697 posts in 689 days


#3 posted 09-06-2016 05:27 PM

I have the Pyle one piece unit and it works as far as I know.

The reality is that measuring cfm accurately with any handheld is a best guess. Depending where you have it set in relation to the center of the pipe will change your air speeds drasticly. If you have it on the edge, versus the center of the pipe, you will get 2 different readings. Also, then you have to make sure you have it set in the same place in relation to how far in front of the pipe as well.

I’m sure there is a jig that can be made to hold it in the same place all the time but I just look at this as a tool to get an idea so no need to really spend so much money on high end tools unless you are actually making a living on dust collection design.

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RobS888

1986 posts in 1310 days


#4 posted 09-06-2016 05:40 PM

The Pyle is nice because you have a remote sensor, so you are able to place the sensor in the same location regardless of where you are. The single piece ones aren’t that easy to read unless the pipe you are testing is near eye level.

-- I always suspected many gun nuts were afraid of something, just never thought popcorn was on the list.

View Redoak49's profile

Redoak49

1951 posts in 1453 days


#5 posted 09-06-2016 06:12 PM

I just posted a blog entry concerning the use of a fan anemometer. What I found is that it can work or it can lead to some really bad data. The problem is that the flow that you read is dependent on the distance from the end of the hose. Holding it directly at the end of a 4” hose will result in very high flow readings and not accurate ones.

If you want to determine the effects of changes to your system, you might try using a cheap water manometer. One of my blogs also shows how I use one.

Please post whatever information that you get as it will be very useful to others to understand how much flow or suction can be gotten from various dust collectors and setups.

View Fred Hargis's profile

Fred Hargis

3942 posts in 1958 days


#6 posted 09-06-2016 07:42 PM

I bought a 0-2” Magnehelic for $25, and a Dwyer pitot tube for $46 (both from e bay). Then I needed about $4 worth of plastic tubing to hook the stuff together. With this you need to take several readings across the duct and average them to get to the CFM, but it works really well. Even so, that pyle unit looks a lot handier, and is probably close enough to be worthwhile (if air flow is of interest to you, as it is to me).

-- Our village hasn't lost it's idiot, he was elected to congress.

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RobS888

1986 posts in 1310 days


#7 posted 09-06-2016 08:28 PM

It sure is, I can check air vents/returns in the house easily as well.


I bought a 0-2” Magnehelic for $25, and a Dwyer pitot tube for $46 (both from e bay). Then I needed about $4 worth of plastic tubing to hook the stuff together. With this you need to take several readings across the duct and average them to get to the CFM, but it works really well. Even so, that pyle unit looks a lot handier, and is probably close enough to be worthwhile (if air flow is of interest to you, as it is to me).

- Fred Hargis


It sure is handy, I can check air vents/returns in the house easily as well.

-- I always suspected many gun nuts were afraid of something, just never thought popcorn was on the list.

View mramseyISU's profile

mramseyISU

419 posts in 1010 days


#8 posted 09-06-2016 08:57 PM

You can them that work with your smart phone. I don’t know where to get them but I had an HVAC guy at my house balancing the system using one.

-- Trust me I'm an engineer.

View Steve Peterson's profile

Steve Peterson

324 posts in 2547 days


#9 posted 09-06-2016 10:25 PM

I use https://www.amazon.com/Floureon-GM816-Temperature-Anemometer-Thermometer/dp/B01DKJMBEU/ref=sr_1_14?ie=UTF8&qid=1473200515&sr=8-14&keywords=wind+speed+meter from amazon for around $11. Not sure what the other more expensive ones do that this one can’t do. It is just a simple curiosity for me and I may only use it once or twice.

-- Steve

View pmayer's profile

pmayer

864 posts in 2530 days


#10 posted 09-07-2016 11:00 PM

An anemometer will give you bogus data because the device itself interferes with the air flow. If you are just looking for a way to establish a benchmark that you can periodically check against to see if you are maintaining performance it’s fine as long as you can establish a consistent approach to taking readings. Where and how you hold the device will have a big influence on the results.

Fred’s approach is the right way to do it. It’s not as easy but it is far more reliable.

-- PaulMayer, http://www.vernswoodgoods.com

View ArtMann's profile

ArtMann

140 posts in 281 days


#11 posted 09-07-2016 11:37 PM

Paul is absolutely right! What you really need is a hot wire anemometer because it is too small to interfere with the air flow. You also need to take into account the fact that the air doesn’t move at the same speed over the whole cross section. The real air flow might be no more than 70 percent of what you calculate using the peak measurement.

View Redoak49's profile

Redoak49

1951 posts in 1453 days


#12 posted 09-08-2016 12:42 AM

There are some very good points being brought up. I wrote a couple of blogs showing how I measured my dust collector performance. I used a hot wire anemometer and took readings at six places across a 6” duct. The locations determined using a standard measuring method for ducts. While it resulted in good data, it was a real pain to do it.

Once you have a performance curve for your dust collector, it is much easier to just check the static pressure to determine your cfm.

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pmayer

864 posts in 2530 days


#13 posted 09-08-2016 03:26 PM

Check out this outstanding post by Redoak where he quantifies the exact issue that I mentioned: http://lumberjocks.com/topics/178538. What Redoak describes is the exact experience that I had, and why I switched to a manometer and pitot tube setup (http://www.dwyer-inst.com/Product/Pressure/Manometers/Digital/Series475). This gear is overkill for just satisfying curiosity of your home shop performance, and what Fred describes will do essentially the same thing for much less money. I believe that approach that Fred uses are the same as those used by dust collection guru Bill Pentz.

-- PaulMayer, http://www.vernswoodgoods.com

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