How about a cyclone shop vac?

J

John Sprung

New member
How well would a cyclone work in the higher vacuum/lower flow neighborhood required for a vacuum cleaner? I'm thinking like 100 - 150 inches of water instead of 6 - 16, and flow rates of maybe 100 - 500 CFM rather than 4000. How would the cyclone design have to change for that?

I'm really tired of shop vacs that cake up and stop sucking just a few minutes after you clean the filter. And the health issues are the same as for woodworking. It doesn't matter to your lungs whether the dust was put in the air by a saw or a shop vac.

The other thing I want to do is get rid of all the dust in my crawl space. It's the same kind of micro-fine stuff that hangs in the air for hours, which makes it miserable to do any work down there. There could be a few cubic yards of it, so using the common shop vac on it is like trying to dig a swimming pool with a spoon.

Another consideration for the monster vac would be to put a simple drop box ahead of the cyclone to protect it from the big chunks. I'm thinking maybe a piece of 1/4" hardware cloth across the drop box to stop paper and string, what do you think?



-- J.S.
 
The thing that makes a cyclone work is air velocity. The inlet velocity needs to be in the neighborhood of 4000 ft/min. We are moving about 1500 cfm of air thru an 18" diam cyclone. To keep the same ratio, if you move 300 cfm of air, the diam of the cyclone would need to be 1/5th as big or 18/5 = 3.6". The inlet diameter on such a baby beast would also be 1/5 the size of our cyclone which is 6". 6/5 = 1.2". That is a very small cyclone, but that's what you would need to get enough centrifugal force to seperate the dust out. The ratios of the cyclone stay the same. In other words, the upper cyclinder is 1D or 1 * diameter. The length of the cone is 1.64 * diam. The inlet is 1/3 diameter. The discharge is 1/2 diam. and the bottom of the cone is 1/3 diam.

You might be better off to just use a big blower with a regular size cyclone and a .5 micron final filter such as we sell.

You really shouldn't need any type of screen. We were feeding chunks of 2 x4s into mine the other day when we finally got it hooked up and running. They don't hurt a thing. It's not likd they slam into anything. The just hug the outer wall and get spun around very fast. :rolleyes:

Ed
 
Thanks for the reply. Unfortunately, for a shop vac, an inlet of 1.2" diameter would be a problem because the vac needs to pick up chunks of material larger than that. Perhaps the right approach is to size the cyclone to pass the largest object to be moved, and accept that that will impair its performance in removing smaller dust particles. The filter would have to trap more and larger particles than it would for a conventional woodworking dust collection system. If the filter is catching a few cups per barrel out of the cyclone rather than a few teaspoons per barrel, that's still well worth doing.

The vac would need to achieve 4000 ft/min with the end of the hose open in order to clear its hose of dust. But we could probably accept much less for brief periods in order to pick stuff up out of deep crevices, then open it up to move the stuff through. I'm not sure that the 4000 ft/min criterion is right for big chunks. When an object occupies a large enough percentage of the cross sectional area of the hose, it would probably act more like a piston in a cylinder or a cannon ball in a cannon, rather than dust in an air stream.

If I figure on using nothing larger than a 3" or 4" hose, then the D/3 rule would mean that a 9" to 12" cyclone would be ideal. A clear one, of course, is also ideal for an experimental unit, because you can see what's happening inside. Perhaps that 15" "Baby" cyclone would be a better starting point than a regular production unit.

The big challenge will be finding a multi-stage blower capable of pulling enough vacuum without cleaning out my bank account.... ;-)


Thanks again --



-- J.S.
 
Oops -- It looks like it accepted my reply yesterday without being logged in.

Another question, how important is it to get the cyclone plumb? How much is performance impaired if it's not exactly vertical? That might be an issue for a portable shop vac.



-- J.S.
 
John,
As to plumb, my answer is I don't think it is critical at all. We did some bench tests with our new impeller and hooked up the baby cyclone and a regular cyclone laying down on the bench. Just for the heck of it we piped up an elbow to a bucket from the bottom of the cyclone and fed some sawdust into it. The spiral of dust was the same as when the cyclone is standing up (as can be seen in our video). However the seperation wasn't as good. We did get a noticeable amount of dust coming out the discharge of the blower. What that tells me is that the cyclone works without gravity, but not as well.

I think a 9" cyclone would be workable for your idea. Are you going to build one? Or are you wanting me to? <smile> I'll need some funding for that project....maybe we could get a "Federal Grant" for researching cyclone design.

Ed.
 
I'd like to build a monster shop vac, but I have a lot of other projects ahead of it. I'm remodeling, doing my own copper roof, and I also have to upgrade the electrical service from 30 Amp two wire 120 Volt to 400 Amp three wire 120/240. That has to happen before I'd be able to power the shop vac. I'm keeping my eyes open for multi-stage industrial blowers, and big single phase motors, in the mean time.

As for cyclones, I'll probably have enough 32 oz. copper left from the roof to make a nine inch. But if you get tired of that 15 inch clear prototype and want to get rid of it, let me know. Seeing exactly what's going on is such a huge advantage for an experimental device.



-- J.S.
 
400 amp service? What are you putting in your shop? Sounds like some heavy welding equipment going in? I won't be ready to get rid of my baby cyclone till I get some gages from Bill Pentz and do some actual air flow tests on it. That might still be a viable product. If I can get at least 800 cfm at about 10-15 ft away from the cyclone it could be used in a small shop. I'll hang on to it till then. If you want to try going to a smaller one I could probably muster up enough scrap plastic for you to try building one. Send me your e-mail and we can talk about it.

Ed
 
The 400 amp service is for the whole property, house and shop together. It's a fairly big house, used to be an apartment building. (I'm not much good at electric arc welding, oxy-acetylene is easier for me.) And I figure why not provide plenty of headroom for future expansion. If I happen to luck into a 50 HP blower for the shop vac, I'd be ready for it. ;-)

In the interim, building a 9" clear plastic cyclone sounds like fun. I could run it ahead of an ordinary shop vac for testing, and probably get a lot more work done between filter cleanings. The best place to e-mail me is at work, John_L_Sprung@Paramount.com.

Thanks --



-- J.S.
 
You must log in or register to reply here.
Back
Top