[OP]
Member
Hi, I'm looking for a cheap velocity meter to measure the efficiency of my vacuum system in my basement work shop. any suggestions where to buy? I will look again on Amazon and Ebay, but some of the used ones scare me. New ones are quite expensive.
Thanks, Abbey Thomas
Guest
It's possible to make a pitot tube with a couple of pieces of copper tube- one is bent to point into the airstream measuring velocity pressure, the other goes strait into the duct so that it measures static pressure. To this a clear "U" of plastic tube is attatched to each of the tubes. The U part, hanging down is filled with water, and when the air goes by it will shift the U. This shift is measured as a pressure in inches of water column. From here use a chart, or Bernoulli's equation to get to flow velocity. It's also possible to get a dwyer magnehelic with the face scaled in fpm
Contributor
Don't know your budget but there is a UEI DAFM2 on ebay for 59.95. I like the hand held type- not as accurate but you can test at each machine port which is the info you really want and still have something to resell if you don't need it. Dave
Contributor
Time for me to jump on my soapbox again.This is yet another example of why it is helpful to give the forum at least some idea of your location; I have among other things a Dwyer in-duct anemometer that I can and do loan to people but if I don't know where you are it's almost pointless for me to offer. Anyways, if you're nearby you're welcome to borrow any of my test equipment.
John
I agree, it really helps when you fill in your location under the "My Profile" at the top, then pick the "About Me" tab, then fill in your location, even if is just the State/Providence/country. I see the first 3 posters on this topic have chosen to omit this valuable step. Hmm, maybe they are in the witness protection program.Originally Posted by John Lanciani
Time for me to jump on my soapbox again.
By the way, to answer the OP's question, I received the CPS AM50 Velocitor for Christmas from my son that works at an HVAC supply house. But I looked it up and its not real cheap, about $190. The pic is showing a reading of 6160 fps on a 4" hose end.
Last edited by Ole Anderson; 01-02-2013 at 1:56 PM.
Contributor
Used Velocitors are around 100-125. thanks, Ole. Didn't choose to omit. Guess when I viewed "about me" I wasn't logged in so never saw the questions. Fixed. Dave
Guest
I like a pitot tube because it can be poked into a hole in the duct, and it's dirt cheap.
Member
Would a wind speed meter work? We use Kestrel brand on the farm, seems like one of them would do what you want. http://www.kestrelmeters.com/product...000-wind-meter is a cheap one. Kestrel also makes HVAC meters to specifically do what you are doing, but more money.
Member
I would recommend a Dwyer Magnehelic and mini pitot tube. The setup will cost about $120 plus some tubing. Look at the Dwyer Instruments site to get an idea of what you want.
The pitot tube has two ports. The one on the tip facing into the airstream measures total pressure (TP). The small ports around the circumference of the tube, perpendicular to the air flow measure static pressure (SP). The difference in these two (what you are measuring with the magnehelic or manometer) is velocity pressure (VP).
The duct velocity is V = 4005 x (VP)^.5 at standard density. Take a VP at multiple points on the cross-section of the duct, convert each one to velocity, average the velocities, then multiply by the duct area and you get CFM. Sounds much more complicated than it is.
Is this a "vacuum" system in the shop-vac sense or a dust collection system in the blower / cyclone / filter sense?
Member
I have got to ask but in that picture you don't have a problem with your cyclone trying to collapse that 4" flexible hose or do you have more blast gates open elsewhere?I agree, it really helps when you fill in your location under the "My Profile" at the top, then pick the "About Me" tab, then fill in your location, even if is just the State/Providence/country. I see the first 3 posters on this topic have chosen to omit this valuable step. Hmm, maybe they are in the witness protection program.
By the way, to answer the OP's question, I received the CPS AM50 Velocitor for Christmas from my son that works at an HVAC supply house. But I looked it up and its not real cheap, about $190. The pic is showing a reading of 6160 fps on a 4" hose end.
The reason I ask is on mine it will collapse 4" flex unless I have at least another 6" blast gate open.
Contributor
Alan, flex with a wire shouldn't collapse. I run between 8 and 9000 fpm in my system and have never collapsed anything. Dave
The limitation to a anemometer is that you can't stick it in the airstream to measure flow with a hood connected. Better to use a pitot tube style you can insert in a small hole in your main run just before the DC or go with a hot wire anemometer.
That hose in the pic is the slinky type from Rockler which will collapse in length to 2 feet and then extend to 10 feet if you pull on it a bit. Under a lot of suction it will collapse in length. No other blast gates were open. The hose has a steel wire that makes the corrugations. Here is another pic showing it even more restricted by being choked down to a 2.5" hose on my belt sander (DC running, no other gates open):
Last edited by Ole Anderson; 01-03-2013 at 8:19 AM.
Contributor
Yes, the blade type anemometer only measures the capability of the system at the port, the Pitot will measure whether the hood further restricts the flow or needs make up air. There is no substitute for velocity though to deal with restrictions in the hood. Dave
Member
Contributor
Alan, that duct is made to compress easily so it tends to do that even with medium suction. I like either the stiffer stuff or in your case a 45 on the end. I bought that kind once as it allows the machine to be moved without pulling out better but the trade off is you need a direct shot. Dave
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