velocity meter

[ABBEY thomas]

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

[Stephen Cherry]

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

[David Kumm]

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

[John Lanciani]

Time for me to jump on my soapbox again.:rolleyes: 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

[Ole Anderson]

Time for me to jump on my soapbox again.:rolleyes: This is yet another example of why it is helpful to give the forum at least some idea of your location

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.

[David Kumm]

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

[Stephen Cherry]

I like a pitot tube because it can be poked into a hole in the duct, and it's dirt cheap.

[Steve Rozmiarek]

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/products/kestrel-1000-wind-meter is a cheap one. Kestrel also makes HVAC meters to specifically do what you are doing, but more money.

[Michael W. Clark]

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?

[Alan Bienlein]

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.

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?

The reason I ask is on mine it will collapse 4" flex unless I have at least another 6" blast gate open.

[David Kumm]

Alan, flex with a wire shouldn't collapse. I run between 8 and 9000 fpm in my system and have never collapsed anything. Dave

[Ole Anderson]

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):

[David Kumm]

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

[Alan Bienlein]

This is what I'm talking about. This is with 6" flex and duct work.

In this picture the blast gate for the planer is closed.
250039
In this one just the blast gate for the planer is open.
250041
And in this one I also opened the blast gate for the joiner along with the one for the planer.
250040

[David Kumm]

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

[Alan Bienlein]

I think I really need to see about an inexpensive velocity meter. The 6" flex that went to my Scms dust hood was even worse until I reconfigured the hood. It would collapse it to the point that it looked like you stepped on it.

[Ole Anderson]

And the nice thing with the collapsible slinky is that you automatically reduce the hose length to minimise long flex and the attendant losses. And I can pull it off the quick connect and stretch it out to clean the shop. I have several pieces a traditional 4" black flex you can have if you want to visit me. Much stiffer.

[David Kumm]

And the nice thing with the collapsible slinky is that you automatically reduce the hose length to minimise long flex and the attendant losses. And I can pull it off the quick connect and stretch it out to clean the shop. I have several pieces a traditional 4" black flex you can have if you want to visit me. Much stiffer.

Ole, have you checked your meter before and after the slinky hose? I'd be curious as to how much flow it costs over say a 5' length- if it is measurable. I know some flex is smooth inside but haven't tried to compare. Dave

[Ole Anderson]

Ole, have you checked your meter before and after the slinky hose? I'd be curious as to how much flow it costs over say a 5' length- if it is measurable. I know some flex is smooth inside but haven't tried to compare. Dave

Summary: Six feet of hose reduced the flow by 24%.

The details: at the end of 6 feet of 4" slinky hose (with a 4-1/8" id fitting open to the air at the end) I had 6550 fpm velocity with 570 cfm. That configuration resulted in the gauges showing 1.4" on the filter and 7.0" on the fan curve. With the hose removed I measured 11,250 fpm and 752 cfm at the blast gate which has a 3.5" inside diameter. Here the gauges showed 2.0" on the filter and 6.1" on the fan curve. Upstream of the 4" (nominal size) blast gate I have 30" of 4" snaplock, a 4"-5" increaser, a 90 degree bend, 66" of 5" snaplock, a 45 and finally a wye as it enters my 7" main. For these tests I held the gauge at the center of the pipe. While the hose significantly reduces the airflow, I am still getting 570 cfm at the router table. Keep in mind that the slinky had 270 degrees of bend (180 at the floor and 90 at the table. Oh, 11,250 fpm is 128 mph. The blast gate was literally whistling. The Velocitor is only rated to 8800 fpm. DC is an Oneida 2 hp Super Dust Gorilla.

[David Kumm]

Ole, flex costs. I would never have guessed you could get that velocity out of a 2hp system with even a few feet of 4" pipe. I bet you will find the blast gate costs too. I know it does on mine. Holding the anemometer in the center does inflate the readings some but still WOW. I'm afraid to try my velocitor for fear of breaking the fan. Did that once all ready. Thanks for the info. Dave

[Ole Anderson]

I would never have guessed you could get that velocity out of a 2hp system with even a few feet of 4" pipe.

It's American Iron baby!:cool:

[David Kumm]

It's American Iron baby!:cool:

Do you know what size impeller? Dave

[Ole Anderson]

Do you know what size impeller? Dave

I don't. Still kicking myself for not measuring it before I installed the unit in a tight spot. Maybe I will email Oneida and ask. Guessing about 13.5 to 14 inch..