I need help/advice on resizing Bill Pentz cyclone.

[johnny means]

I want to build a Pentz cyclone using a 10 hp, 3450 rpm motor with a 17" impeller. I do not have or know how to use Excel. Any advice or information would be appreciated.

[Tom Veatch]

Do you want to move enough air to use all or a significant portion of the 10hp, or is it just that you happen to have that size motor and impeller available? Your impeller is only an inch larger than the one I use with a 5HP motor on a "standard" sized Pentz cyclone. With a properly sized blower housing, it should be a fairly good dimensional fit to the "standard" sized cyclone.

If you really need to move enough air to use the full 10HP, without running any numbers to verify the gut feeling, I'm guessing you're going to need something on the order of a 40 to 50% increase in linear dimensions. That number is based on my Pentz cyclone with a 16" impeller, running with duct work connected, absorbing about 3HP. Since power requirements in aerodynamic applications seem to run to cubic functions and, in round numbers, 10HP is about a 3x increase in power, the cube root of 3 is about 1.44.

[johnny means]

I am looking to move as much air as this motor/ impeller combination is capable of moving.

[Tom Veatch]

Thinking a little deeper on my first response, the cubic relationship is proportional to flow rates which are proportional to squares of linear dimensions. So instead of 40 to 50% increase, 20% increase in linear dimensions would probably be more appropriate. That also requires increasing the area of the ductwork to support the larger flows and keep the pressure losses to reasonable amounts.

20% increase in linear dimensions should translate to about 1.2 squared or about 1.44 increase in flow which would translate to 1.44 cubed or about 3 times the power required/absorbed from the motor.

Remember this is all "back of the envelope" estimation. Detailed analysis of specific configurations would be needed to verify those estimates.

[Glenn Roberts]

Johnny, I don't think the excel spreadsheet will allow for a motor size above 5hp. Have you tried emailling Bill for help?
From what I have read on his site ( and the spreadsheets etc) You could scale up the 16" impellor blower plans (form his site, try a plan printing service as it will end up nearly 2.5 feet square) and if anything I would expect the cyclone to become smaller in diameter,with a shorter cone. I am guessing your duct size would remain at 6" for most machines.

If you check the dimensions on the cyclone plans (for the various size motor/impellor combinations, you might be able to get an approximate 'scaled' value for your combination.
On Bill's site, I think he mentions the size of larger 'commercial' units???

I would ask Bill.

[Tom Veatch]

...if anything I would expect the cyclone to become smaller in diameter,with a shorter cone. I am guessing your duct size would remain at 6" for most machines.


Nope. For large, higher power cyclones, check the dimensions in here, http://isystemsweb.thomasnet.com/Asset/cyclones2009.pdf. The higher the flow rate, which is what the OP indicated he wanted, the larger the cyclone.

If you're going to increase the mass flow rate, there's two ways to do it. You can increase the flow velocity in the same size ducts - very power hungry way to do it, power required increases as the cube of the velocity. Double the flow rate doubles the velocity requiring approximately 8 times as much power. Or, you can increase the amount of air flowing at the same velocity - closer to a double the flow double the power - but requires 40 to 50% greater duct area to get double the flow rate at essentially the same power per cubic foot of air moved.

It's not a simple problem, but I'll stick with my earlier comments. The "sweet spot" on my Pentz cyclone seems to be with 6" ducts and a power consumption of about 3HP. I get very efficient separation with those parameters. Johnny wants to use all of his 10HP to move as much air as possible. Gonna have to go up to about 10" on the duct work and about a 20% increase in the cyclone dimensions to keep the power required under control and the velocities up to where they need to be. Even the 20% increase in cyclone dimensions may be a little on the small side. But going very much larger than that will slow the swirl velocity and lower the separation efficiency. Going smaller than that will increase the velocity, increasing separation efficiency, but costing much more power to move the same amount of air.

[Alan Schaffter]

If the cyclone and ducting are not sized properly, that big 10 hp motor could be drawing one heck of a lot of amps!! I agree with Tom, 16" is a bit small of an impellor for a 10 hp motor. To take full advantage of a 10 hp motor you need the proper size impeller, cyclone, and ducting. Overpowering is not necessarily bad, just inefficient.

[johnny means]

If the cyclone and ducting are not sized properly, that big 10 hp motor could be drawing one heck of a lot of amps!! I agree with Tom, 16" is a bit small of an impellor for a 10 hp motor. To take full advantage of a 10 hp motor you need the proper size impeller, cyclone, and ducting. Overpowering is not necessarily bad, just inefficient.

Actually, it was a 17" impeller and this configuration is coming directly off of a dust collector.

Anyway, after looking at the diagrams from the site listed above I have nixed the large cyclone idea (way to tall). My next idea is a centrally located blower drawing through a pair of cyclones on either side. Any reason why this wouldn't work or problems to watch out for.

[Alan Schaffter]

Actually, it was a 17" impeller and this configuration is coming directly off of a dust collector.

Anyway, after looking at the diagrams from the site listed above I have nixed the large cyclone idea (way too tall). My next idea is a centrally located blower drawing through a pair of cyclones on either side. Any reason why this wouldn't work or problems to watch out for.

FYI- there is more disadvantage underpowering a cyclone than overpowering one. Underpower- low CFM, velocity, poor separation. Too much hp- just wasting a little KWh. 1o hp/17 hp- the basis for a killer system that will suck up dust, small rodents and the family cat!!!

I don't understand- why too tall? Put it outside- better in many respects or if you have enough height for a regular cyclone you should have enough for a slightly larger one required by a 10 hp blower with 17" impeller- if you configure it as a push-through where the motor and blower are not mounted on top. There is absolutely no good reason if the impeller is steel, that you can't separate the cyclone and blower in a "push-through" configuration. I have been doing that for over 7 years, first with a cyclone I made based on the old Wood Magazine design, then a Pentz 3D* I made (*length is 3 times diameter of upper cylinder- as opposed to 1.64D in the typical Pentz/ClearVue cyclones. A 3D supposedly separates fines better than a 1.64D). Arguably a "push through" cyclone also has better separation and less internal resistance than a traditional "pull through" cyclone too. In addition to less height, the other BIG benefit of a "push-through" and the main reason I went this way, is that you don't need an airtight dust drum, you can just connect a plastic trash bag to the bottom of the cone. When it is full, remove it, tie the top, and just carry it to the curb- no mess. Here are pics of my old and new cyclone systems.

A 3 hp motor w/14" impeller blower unit I pulled off an old bag type DC connected to the old Wood Magazine designed cyclone in a "push-through" configuration (mounted outside my old shop). The blower inlet is on the far side. The 6" exhaust coming out the top returns air to a shop mounted cartridge filter:

http://www.ncwoodworker.net/pp/data/500/medium/P2240015.JPG

New Pentz 3D cyclone before installation in my new shop (notice how tall a 3D is! You don't need a 3D):

http://www.ncwoodworker.net/pp/data/1329/medium/P10101151.JPG

Original motor/blower unit and new cyclone mounted in my new shop utility space:

http://www.ncwoodworker.net/pp/data/1329/medium/P10100382.JPG

In operation:

http://www.ncwoodworker.net/pp/data/1329/medium/P10100531.JPG