Thread: Busting some cyclone myths

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Hi Tim, great work. Looks like a nice cyclone and good bit of data.

Originally Posted by Muchacho

This also presents a contrasting view to claims often made that the inefficiency of even well designed cyclones rob a low powered dust collection system of too much airflow. The chart shows the maximum airflow achieved through the cyclone of around 1000 cfm with only 8mm of static pressure. Putting this into context, this pressure loss is the equivalent of about 3.1 metres of 150 dia pipe. (3.1 inches per 100 feet at 1000 cfm from pipe loss charts)

Can you explain this statement? Are you saying you believe that the cyclone only adds 8mm of static pressure (I assume not) or that you achieved 1000 cfm at 8mm of static pressure, with the static pressure measured at the point where you have the manometer tube sitting in the duct just before the anemometer? The common view seems to be that the cyclone adds around 2.5" of static pressure at probably around 1000 CFM (my assumption).

I wonder how your cyclone would go with a larger impeller / motor combo. What are the approximate dimensions (diameter and length) of your cyclone? If you could get 800+ CFM at around 6" or so of static pressure it would be great for permanently ducted setups.

How did you vary the static pressure in your test? A blast gate or similar?

Final question. Is this ducted outside or through filters? If outside, do you think that wind conditions or the day(s) you tested could have accounted for the differences measured between the cyclones (more / less back-pressure)? I know my Clearvue draws more / less amps depending on the wind conditions outside.

thought it is written, he will come

Originally Posted by Opelblues2

thought it is written, he will come

?? Confused.

Originally Posted by woodPixel

What a shame you are not in Oz, I would buy one of those off you!

The plans to build a cyclone are freely available on Bill Penz's site for anyone who wants to build one. The single biggest problem in Oz is sourcing a suitable sized impeller but Clearvue can do that for you. I supplied quite a few impellers and I would be interested in seeing if the projects ever got finished.

Can you explain this statement? Are you saying you believe that the cyclone only adds 8mm of static pressure (I assume not) or that you achieved 1000 cfm at 8mm of static pressure, with the static pressure measured at the point where you have the manometer tube sitting in the duct just before the anemometer? The common view seems to be that the cyclone adds around 2.5" of static pressure at probably around 1000 CFM (my assumption).

Hi Dom, Thanks for your comments.

[Edit]
As you correctly point out, I have got this wrong. The minimum SP reading is not necessarily the pressure loss of the cyclone. I'll try to get this measured properly and repost.

The 2.25” pressure loss figure is normally attributed to Bill Pentz without any reference to what airflow rate it is measured. It is not a constant figure but it will vary with airflow. Frictional losses in pipes and fittings under turbulent flow are proportional to the square of the airflow. So for example if the 2.25" figure is measured at 1800 cfm, at 900cfm the pressure loss will only be a quarter of this.
[End Edit]

I wonder how your cyclone would go with a larger impeller / motor combo. What are the approximate dimensions (diameter and length) of your cyclone? If you could get 800+ CFM at around 6" or so of static pressure it would be great for permanently ducted setups.

Likewise, I’m keen to see how it would go with a larger fan. Referring to the data on the Cincinatti Fan website, a fan with 8” inlet and 14”x 3 ¼ ” backward curved impellor running at 2850 RPM (50Hz) will achieve this.
Dimensions of the cyclone are approx 470mm diameter and 1350mm tall.

How did you vary the static pressure in your test? A blast gate or similar?

I tried using a “hard” restriction to throttle the flow but found it caused too much turbulence and unsteady flow in the test pipe. For these tests I used multiple layers of shadecloth held over the inlet. For the second data point it was one layer, then 2, 4, 6 etc. For greater restrictions then threw old t shirts and finally a towel over the inlet.

Final question. Is this ducted outside or through filters? If outside, do you think that wind conditions or the day(s) you tested could have accounted for the differences measured between the cyclones (more / less back-pressure)? I know my Clearvue draws more / less amps depending on the wind conditions outside.

I haven’t noticed any variation with weather conditions. Mine is ducted outside into a pretty sheltered area between shed and fence.

Originally Posted by woodPixel

What a shame you are not in Oz, I would buy one of those off you!

It is designed to fit a carton which NZPost will ship to your door for a very reasonable figure. If you are interested please feel free to send me a PM.

Australia Post won't go anywhere near an item of that size regardless of how little it weighs, yet it can be sent from overseas and they'll deliver it without a squeak! They also have arrangements in place with some companies to accept oversize 'returns'. Then they'll winge that they're not making any money.

Sorry, off topic. It's just something that bugs me.

Originally Posted by woodPixel

I meant for the cyclone part in fibreglass.

Build it using thin plywood and then glass the inner surfaces.

I'll be interested to hear how you go with a larger impeller combo. Hopefully you get the chance to try it out. I'd personally stick a 15" on there with a 3+ HP motor.

Originally Posted by Muchacho

Hi Dom, Thanks for your comments.
Yes that’s right, 8mm static pressure at just under 1000 cfm. This sounds unbelievably low but it must be realised that this is taken at a much lower airflow than other pressure loss figures often quoted.
This is significant as frictional losses are proportional to the square of the airflow so moderate changes in airflow generate large changes in frictional loss.
I believe that the 2.25” pressure loss figure is normally attributed to Bill Pentz without any reference to what airflow rate it is measured. I believe that the SP figure needs to be taken at 1800 cfm otherwise the cyclone’s aerodynamic efficiency will need to be considered pretty average.

I'm not trying to be critical but I don't think you have this right. If you are measuring up-stream of the cyclone, as in your photo, then the static pressure you are measuring is the pressure drop across your test ducting. To get the pressure drop across the cyclone you would need to measure static pressure downstream of the cyclone, just at the inlet to the impeller.

Also, the 2.25" "flat-rate" figure often thrown around for adding a cyclone frustrates me as well. It will only be 2.25" at a particular airflow so isn't really useful for determining the loss in every system, particularly smaller impeller/flow systems.

Originally Posted by DomAU

I'll be interested to hear how you go with a larger impeller combo. Hopefully you get the chance to try it out. I'd personally stick a 15" on there with a 3+ HP motor.



I'm not trying to be critical but I don't think you have this right. If you are measuring up-stream of the cyclone, as in your photo, then the static pressure you are measuring is the pressure drop across your test ducting. To get the pressure drop across the cyclone you would need to measure static pressure downstream of the cyclone, just at the inlet to the impeller.

Thanks for this, you are absolutely correct. I've edited my posts above.

Originally Posted by DomAU

I wonder how your cyclone would go with a larger impeller / motor combo. What are the approximate dimensions (diameter and length) of your cyclone? If you could get 800+ CFM at around 6" or so of static pressure it would be great for permanently ducted setups.

+1

Tim, your pressure/flow graph indicates little or no difference at the higher flow rates, which is reassuring for anyone considering going with the Clearview, as I am. If I have any misgivings about the Clearview cyclone (not the impeller and its controls which are spot on) is that the inlet is on the opposite side of the cyclone to where I would expect it to be, given the direction of fan rotation.

Some stats with a larger impeller on both your left and right hand inlets models would be even more reassuring for both your cyclone and the Clearview options.

Isn't the clearvue available in both left-hand and right-hand versions to cater for different installations?