Dust Collector too small (HP) and locating in garage create dust on cars?

[David Kumm]

I think you guys have hit on something with the inlet speed. The Clearvue was designed specifically for 6" mains with an inlet velocity in the 5-6000 fpm range. The 55-60 sq inch inlet on the Torit is likely to reduce the speed to the same range when running with 8". The working range of my unit is between 1200-1600 cfm . Higher is possible but not with a 5 hp motor so to hit the higher numbers the system would need the 7.5 hp motor and then Torit moves to a 24" cyclone to again slow the speed down. As to the filters, I built my own plenum but if it worked out I would use the one supplied by Torit and replace two of the four tubes with cartridges and run a combination of both. The 100 sq ft that Torit comes with works much better if expanded and filtration is improved when the air isn't forced through. I run one 100 sq ft cartridge and four tubes equalling another 100 sq ft on mine and am considering replacing one of the tubes with another cartridge. My cartridge is spun bond rather than hepa but the Dylos stays so low I don't know what I would really gain with the Hepa and of couse I would have to change them all or it wouldn't make sense. Dave

[Michael W. Clark]

There are two primary things that affect cyclone efficiency. Ther first is pressrue drop (DP). DP is representative of the force being exerted on the particles to move them to the outside wall where they can be collected. The higher the DP, the greater the force, and the higher the efficiency. The second is the size of the cylone (diameter and height). The size is representative of the retention time in the cyclone. The more time the particle has to move to the outside wall, the greater the chance that it will be collected. Of these two things, cyclone size has a larger impact on efficiency. Of course, this is a general statement and there are a lot of variables that affect efficiency.

Ian, the company I work for developed some computer programs like you are referring to for our cyclones. Our cyclones are high efficiency industrial cyclones, but have some significant differences from the cyclones avaialble to us retail. We developed these computer models through about 5 years of emperical testing and correlating the data. In my opinion, emperical testing is the only way to truly get cyclone efficiency. This allows us to guarantee and warranty our efficiency. To my knowledge CFD (computational fluid dynamics) computer analysis does not give repeatable/reliable results for cylones, but maybe it is close enough for what you are suggesting. I think you would still have to do some emperical testing to prove the CFD analysis worked. The biggest problem for CFD is that no-one has been able to mathematically describe the flow patterns inside a cyclone accurately and repeatably.

That being said, I am not surprised by the efficiency listed for the 1 micron particles on the Donaldson units. I am more surprised by the efficiencies quoted for the retail units. It is very difficult for a cyclone to get high efficiency on 1 micron dust. Usually, when you are trying to filter this low, you either have a fabric filter or wet scrubber. A cyclone is usually not practical for this type of efficiency on this dust size. If we were talking about 99% on 5 micron, then a high efficiency cyclone would probably do that on wood dust. I'm not saying it can't be done, just saying that I doubtful that you could buy it for the prices advertised and the sizes given.

I'm not sure why we need 99% on 1 micron from the cyclone when there is an afterfilter. The only reason to have a high efficiency cyclone is to reduce the cleaning of the afterfilter, correct? Obiviously, if the filter goes too long without cleaning, your system volume drops due to the back pressure, and you lose collection at the hoods. Just thinking, which is dangerous, why not use a static pressure gauge after the fan outlet to monitor backpressure from the afterfilter? Once it gets to a set pressure, then you clean it.

[David Kumm]

good info Michael. I watch the amp draw on my vfd to determine filter effectiveness. I know the amp draw with certain ports open when the filters are clean and when the draw goes down a few tenths I clean them and it returns to normal. Not really scientific but makes me feel better. Is there a website with info on your cyclones. Would be interesting to read even if not relevent for our use. Dave

[Michael W. Clark]

good info Michael. I watch the amp draw on my vfd to determine filter effectiveness. I know the amp draw with certain ports open when the filters are clean and when the draw goes down a few tenths I clean them and it returns to normal. Not really scientific but makes me feel better. Is there a website with info on your cyclones. Would be interesting to read even if not relevent for our use. Dave

http://www.fkinc.com/cyclones.htm

There are also some technical articles on the site regarding cyclone operation and design. Some of the project examples are pretty interesting too. (for geeks like me anyway)
Mike

[ian maybury]

What you have to say on size Michael doesn't bode well for the shortie cyclone types we see around. That said extra delta P presumably stops helping eventually - otherwise it'd be a case of the faster the inlet air speed the more efficient a cyclone would be??

My muttering about 99% cyclone efficiency is mostly a reflection of the claims I've seen about - it sounds like the reality may be that they don't get near that. For sure the issue filter life, but being tight, and again being influenced by what one reads on some of the forums I guess I'd been hoping that my nice new Donaldson cartridges might last for a long time. Cleaning is fine, but it sounds like there's only a limited number possible before the filter blinds up and/or the media starts to leak.

I was thinking CFD models Mike, but have no experience. It wouldn't surprise me too much if there isn't still an element of the unpredictable black art about cyclones - that like in most other engineering calculations it's often necessary to get an empirical value or two to get calibrated. That said I saw a paper recently by a European university group which seemed to suggest they were modeling cyclones, but it's quite likely I read more into it than was advisable.

If predicting performance entails a lot of testing then the chances are that most cyclone makers would regard the output as proprietary information, and probably wouldn't be very inclined to release it to a bunch of DIY-ers - at least not for any price we could reasonably hope to pay. Do you have a good R&D guy in your company that we could kidnap?

ian

[Phil Thien]

Those cyclones are quite Pentz/Clear Vue like.

Someone told me that the Donaldson-Torit design dates back a couple of decades. Not sure if that is correct or not.

[David Kumm]

Someone told me that the Donaldson-Torit design dates back a couple of decades. Not sure if that is correct or not.

I believe that as mine is old and the only difference I can see is the whole thing is welded rather than bolted together. The inside vane and baffle looks like the current pictures. Dave

[Michael W. Clark]

I can't comment on the shorties very well. They do have quite a bit of retention time, but you reach a point where you start losing efficiency with a short cone and body.

[ian maybury]

Realistically speaking the basic work on figuring out cyclones seems to have been done long ago. I think Bill has said before now that his design drew on the model endorsed by one of the industry bodies, but I can't quite remember which one...

ian

[Michael W. Clark]

The bulk of our work was done back in the 70s and 80s but have made tweaks and improvements along the way for specific applications.