CV1800 installation

[Michael W. Clark]

Janis,
It doesn’t matter if the flow is 1900 CFM or 900 CFM. If you are happy with your investment and performance that you are getting, then plug it in, run it and be happy.

I think others are questioning your numbers because they do not seem doable. I would be just as skeptical regardless of who built the system. Like I said in another thread, I do not own either the CV or Oneida collectors nor am I affiliated with either in any way, so I am unbiased. I am a licensed ME and design/sell industrial dust collection systems and high efficiency cyclones as my day job. Let me take a stab to explain why I (and maybe others) am skeptical of the numbers you posted. Maybe there is something I am missing?

The SP loss through 10 feet of 6” pipe at 1900 ACFM (I assumed galvanized, I do not have friction factors for PVC as this is not allowed in industrial applications) is 13.6”wg. This is the pressure you would measure at the cyclone inlet. Assuming the cyclone has an 8” diameter inlet, an equivalent medium efficiency industrial cyclone will have a pressure drop almost 10 times the value you posted for your cyclone at 1900 CFM and same inlet velocity (~90 FPS). Let’s assume your cyclone has half the pressure drop of an industrial cyclone, so 10”wg at 1900 CFM.

Let’s also assume you need about 1”wg of static to get the air from the fan outlet and across the filters.

This gives you a pressure of approximately 24”wg that the fan must overcome to deliver 1900 CFM with 10 feet of 6” duct and a plain end. This is not a “no load” condition. Using the air power equation, you would need about 14 BHP, assuming an air density factor of 1.0 and a fan efficiency of 50% (typical for RT wheels). Even if your cyclone DP stated is correct, you would need about 9 BHP. See the Cincinnati Fan catalogue for SPB blowers for an approximation.

I think your anemometer is giving you a bad reading. It may be seeing an equivalent of 1900 CFM at the middle of the duct, but an open end duct draws air from all around (there are some good graphs in the ACGIH manual depicting this). This will reduce the average duct velocity significantly. An open-end duct is very inefficient for dust capture and getting air into the duct. When taking pitot tube readings, you never read (or at least never record) the velocity at the center of the duct. Only in rare circumstances would it approximate the average velocity in the duct. I have taken multiple readings across the face of 6” ducts and still not get them to agree with pitot readings downstream in the same duct.

My advice would be to not sweat it and enjoy your system. Or, if you still want to verify the readings, take some SP readings and an amp reading of your motor amps. Then enter the fan tables for similar conditions with a similar size fan and compare it to your anemometer readings. Alternatively, take a pitot tube reading at the cyclone inlet.

Best,
Mike

[Janis Stipins]

My advice would be to not sweat it and enjoy your system. Or, if you still want to verify the readings, take some SP readings and an amp reading of your motor amps. Then enter the fan tables for similar conditions with a similar size fan and compare it to your anemometer readings. Alternatively, take a pitot tube reading at the cyclone inlet.

Hi Mike,

Good advice all around. Ultimately my tools are clean and the air is clean in my shop (at least according to my particle counter), so I agree that the exact flow is not as important.

That said, I would like to get a reading of the amps used by the motor, and take some actual SP measurements using a pitot tube, just to see what makes sense.

The SP loss through 10 feet of 6” pipe at 1900 ACFM (I assumed galvanized, I do not have friction factors for PVC as this is not allowed in industrial applications) is 13.6”wg.

Holy cow. That's very different than what I've seen in many places, including this calculator here: http://www.engineeringtoolbox.com/du...oss-d_444.html

Everywhere I've seen puts the loss somewhere around 2" (or less, since PVC is smoother than HVAC duct). What's the discrepancy here?

The inlet at my cyclone is 6", not 8", if that makes a difference in your calculation.

Now I really am going to have to pull out the pitot static tube, just to see. :-)

-Janis

EDIT: That calculator I linked to gives a loss of 2.3" over 10' of 6" galvanized HVAC duct with turbulent flow, at 1900 CFM. Bill Pentz's spreadsheet, which is apparently using the same formula, also gives 2.3" of loss. Again, that's for galvanized, which has a Hazen Williams coefficient of something like 130, as opposed to PVC, which is something like 150. And this is a straight line duct into the intake, well over 10 diameters long, which should be enough to establish a very non-turbulent flow. I don't see how you're getting anywhere near 13" of pressure loss in your calculation.

[David Kumm]

I've done a fair amount of experimenting with a fan blade anemometer and several types of impellers and don't believe the 1900 cfm number either but not sure it matters. A 15" backward curved impeller will provide approximately the same cfm whether sold by Oneida, rGizzly, or Clearvue. Depth of the fins makes a little difference and each cyclone might have a little different pressure drop and the filters might might differ too. CV may have a little less drop and better separation but buying one over the other for additional cfm isn't relevant. My experience with a 15" Oneida fan was that it was designed in such a way to never overamp a 5 hp motor so I could not max out the amps on my system. A 16" impeller will deliver more cfm under higher sp but there is a limit to what cfm you can get from a BI or BC fan given they are designed as a low pressure unit. They provide lots of cfm at low pressure but the design that saves the motor from burning out also reduces the cfm as pressure increases much more quickly than a radial fan. If I were running 6" mains ( which I believe are seldom the right size ) I would run the 16" impeller to overcome the restriction of the pipe. My ONeida 15" would provide close to 1700 cfm at the closest gates with an 8" main opening to two 5" ports but fell below 1000 cfm down then line as the sp added up. It took a 7.5 hp radial to pull high cfm though a long length of 7" pipe at 1900 cfm. If you want to increase cfm for either CV or Oneida, increase the main to 7". Not that much difference between the two. Dave

[Brett Bobo]

All of this points to just doing a full-blown CFD analysis of the system so fire up the super-computer . Jokes aside, Mike is a very knowledgeable guy on the topic and recently helped me as well with my cyclone setup. Of course, that's not to imply that you're not knowledgeable as well--sounds as though your background is similar. I'll agree with him that if the system is performing to your satisfaction, then that's most important.

[Art Mann]

I am going to stop posting but I will have my final word. First, you measured the velocity of the air at the center of a piece of duct and concluded that was a good approximation of the average air flow. Nothing could be further from the truth. If you will take the time to Google "dust collector inlet air velocity" or something similar to that, you will find many velocity mapping graphs that confirm my claim. The fact that you even thought that for a moment tells me you have no practical experience in the discipline. I have had to do these sorts of measurements to verify the performance of million dollar environmental test chamber systems in the automotive industry on more than one occasion. I would estimate the real average flow rate is between 0.6 and 0.7 of the center velocity. I find it interesting that if you take your measurement and multiply it by my correction factor, you get numbers that are very much like those the engineers measured in the Wood Magazine article.

By the way, for the benefit of someone who implied I am some sort of advocate for Oneida, that is just wrong. I don't have any of their equipment and have never even spoken to anyone who works there. My goal is to promote the truth. I have read many almost mythical claims for the performance of Clearvue cyclones over the years but I have never seen an actual study conducted in anything like a scientific way to compare their equipment with that of other companies. The Wood Magazine was the first for me. While I am not entirely satisfied with their procedures compared to how I would have done it, I do think their information has some value.

[Janis Stipins]

OK, so this is an interesting discussion, and it's very possible that I'm going to learn that I was wrong in both my measurement and my rough estimate of the flow.

But I have a serious question for those who have a hard time believing that I measured right.

What do you think of the 5 HP Oneida's published air flow, with no ducting attached, of 1860 CFM? Is that hard for you to believe too? If not, why not?

-Janis

[Michael W. Clark]

That calculator I linked to gives a loss of 2.3" over 10' of 6" galvanized HVAC duct with turbulent flow, at 1900 CFM. Bill Pentz's spreadsheet, which is apparently using the same formula, also gives 2.3" of loss. Again, that's for galvanized, which has a Hazen Williams coefficient of something like 130, as opposed to PVC, which is something like 150. And this is a straight line duct into the intake, well over 10 diameters long, which should be enough to establish a very non-turbulent flow. I don't see how you're getting anywhere near 13" of pressure loss in your calculation.

Hi Janis,
The loss of 2.3" is correct for the duct losses. However, you have to include power and energy to accelerate the air from 0 FPM up to your duct velocity of 9677 FPM (1900 cfm in a 6" duct). This acceleration is equal to one velocity pressure. You also have the losses associated with a plain end duct, this is 0.93 velocity pressures. One velocity pressure equals (duct veloctiy / 4005)^2 for standard air. In your case, 5.84"wg. So the SP at the cyclone inlet would be 2.3" (duct loss) + 5.84" (acceleration) + (.93*5.84) (for the plain duct) = ~13.6"wg.

Mike

[Michael W. Clark]

What do you think of the 5 HP Oneida's published air flow, with no ducting attached, of 1860 CFM? Is that hard for you to believe too? If not, why not?

-Janis

Just a guess, but I would suspect they used a large duct (10" maybe) with a bellmouth inlet that has an entry coefficient of about 0.04. Basically they have very, very little system loss and they may have even added some straight duct to the fan outlet instead of the filters. Straight duct will give the fan better performance than no duct at all on the fan outlet. Maybe they explain it on their website how the test was done?

Mike

[Janis Stipins]

I would estimate the real average flow rate is between 0.6 and 0.7 of the center velocity. I find it interesting that if you take your measurement and multiply it by my correction factor, you get numbers that are very much like those the engineers measured in the Wood Magazine article.

That's a good point. Let's be a little more careful about it, though.

To start with, what I actually measured on the anemometer was 9600 CFM, in the center of the pipe. Based on that I figured just over 1880 CFM (remember, the Oneida advertises 1860 CFM under similar conditions). But you're right, the flow is not uniform, and that's got to be an overestimate; the question is how much.

In my case I'm using a fan that averages over a circle of nearly 3" diameter. So assuming I was holding the vane dead center in the pipe, I'm averaging over only 25% of the intake area. If the average over the whole intake is actually 70% of my reading --- which is the generous side of your guess --- that would mean that the part I'm not measuring would have to be only 60% of what I'm reading in the middle. ((X + 3*.6X)/4 = .7X) That would mean that if I move my flow meter 3" to the side, the FPM would cut almost in half.

That sounds pretty extreme to me, but I can give it a try and see what happens.

-Janis

[Phil Thien]

To start with, what I actually measured on the anemometer was 9600 CFM, in the center of the pipe.

When you measured the center of a 6" pipe with a 3" weather vane anemometer, did you have to partially obstruct the pipe with the body of the anemometer? That has been a challenge for me with my Kestrel (and one of the reasons I went w/ such a small anemometer in the first place).

Nonetheless, with my Kestrel I'd say readings on pipes are within .85x for up to 4". I had some individual readings from 6" and 8" pipe in a spreadsheet that I'm afraid I didn't save, so I can't check those.

[Janis Stipins]

Hi Janis,
The loss of 2.3" is correct for the duct losses. However, you have to include power and energy to accelerate the air from 0 FPM up to your duct velocity of 9677 FPM (1900 cfm in a 6" duct). This acceleration is equal to one velocity pressure. You also have the losses associated with a plain end duct, this is 0.93 velocity pressures. One velocity pressure equals (duct veloctiy / 4005)^2 for standard air. In your case, 5.84"wg. So the SP at the cyclone inlet would be 2.3" (duct loss) + 5.84" (acceleration) + (.93*5.84) (for the plain duct) = ~13.6"wg.

Mike

OK, we're getting closer. Earlier you said that the loss in the 10' of pipe was 13.6"wg, but now we agree it's 2.3".

You're estimating that the acceleration pressure internal to the system is 5.84", but both Oneida and Pentz say that it's more like 2.25" for a cyclone. Again, no need to argue; we can just measure and see.

My last point of confusion is the end duct pressure. My understanding is that this applies to blowing air, like in a heating/cooling system, as the high-velocity air comes out into a room of essentially still air. I didn't think it applied to suction systems, which have very different dynamics. Am I wrong about that?

-Janis

[Janis Stipins]

When you measured the center of a 6" pipe with a 3" weather vane anemometer, did you have to partially obstruct the pipe with the body of the anemometer?

Good question. The one I'm using is a General Tools CFM Master. Its vane is connected to the body by a cord, so the obstruction isn't that much more than the fan itself. But you're right, it's not zero obstruction.

-Janis

[Michael W. Clark]

OK, we're getting closer. Earlier you said that the loss in the 10' of pipe was 13.6"wg, but now we agree it's 2.3".

You're estimating that the acceleration pressure internal to the system is 5.84", but both Oneida and Pentz say that it's more like 2.25" for a cyclone. Again, no need to argue; we can just measure and see.

My last point of confusion is the end duct pressure. My understanding is that this applies to blowing air, like in a heating/cooling system, as the high-velocity air comes out into a room of essentially still air. I didn't think it applied to suction systems, which have very different dynamics. Am I wrong about that?

-Janis

I said the SP at the cyclone inlet would be 13.6. Duct frictional losses are 2.3. The rest are acceleration losses and energy required to get the air in the duct based on the hood configuration. Blowing air out the duct is a different animal.

The pressure drop across the cyclone is in addition to the 13.6 at the inlet. I doubt 2.25"would touch it at 1900 cfm. This not the same as acceleration losses.

That 2.25 sounds more like a hood SP than a cyclone pressure drop. If you were flowing 4000-4500 FPM it would be reasonable. The hood SP is measured in the duct about 2-3 diameters from the hood.

[Jim German]

So just to throw another data point to add some more confusion into the discussion. I took some measurements of my CV1800, which has been in use for awhile so the pressure drop on the filters is probably somewhat higher than on a fresh install. I measured ~900CFM (accurate +/- 10%) at the end of my run, which is an 8" main with 10' of 6" flex in a very curved layout.

I'll do a full write up of my installation after I finish taking my particle count readings.

[John Coloccia]

So just to throw another data point to add some more confusion into the discussion. I took some measurements of my CV1800, which has been in use for awhile so the pressure drop on the filters is probably somewhat higher than on a fresh install. I measured ~900CFM (accurate +/- 10%) at the end of my run, which is an 8" main with 10' of 6" flex in a very curved layout.

I'll do a full write up of my installation after I finish taking my particle count readings.

Is that about what you expected or did that come in low?