Dust collection question

i am assuming that i am not using the full capacity of my duct work now.

Is what you have now keeping up with what you are doing?

If so why mess with something that works, if not you must be doing a bunch of sawing, planing and sanding over there bozz.....I knew you had gads of lumber stored up, must be you got ole Webster out there making dust too. :thumb:

As far as a answer to your question, I'm not smart enough to have an intelligent answer for you.....but I can cheer you on from the sidelines!
 
.....and as far as pulling tractors and ductwork go, here is my neighbor Jerry Van Dorpe pulling the Screamin Demon II in Louisville, check out the flexible ductwork they use to get rid of the exhaust indoors.

000_0033.jpg


.....sorry bout the hijack, Chuck started it....:rofl:
 
Hey I cannot help on the ductwork but i gotta ask Chuck on the hijack thread going here at the same time, why he gotta blame the rednecks for a 4 engine tractor. Any guy that can put that together and make it work is a rocket scientist leave the poor rednecks out of it.:rofl::rofl:

(John Wayne defender of the rednecks) Cheers:D:thumb:

BTW Chuck how did you get to do the nice large picture? We used to your tiny versions.
 
Last edited:
Rich is close on his description. The fans create a low pressure region, and fluid mechanics can explain flow changes after that. The lower the pressure at DC intake the higher the flow. The question, how much lower of a pressure will be created by two DC instead of one?

DC like pumps have a cuve of responses. If you unhook the piping, they have a very minimal pressure drop from intake to exhaust and move a lot of air. Blank off the intake, and they have no flow and maximum pressure drop, represented by static suction head, often listed on DC spec sheets.

Now with two working together, somewhere on that curve of responses, you will have more than 50% the original flow going through each one, but less than 100% of the original flow going through each one, and a lower line pressure at the intake to the two DC than the one single DC.

I work with pumps and incompressible flow, not fans/compressible so that's about as far as I'm competant in. Someone sharp with fans could probably estimate it knowing the rpm, OD, and height of the fan blade though. Without a performance curve for the fan on the DC, or testing to basically determine it experimentally I couldn't provide an answer. One good way to measure the pressure change though - put a clear hose off the suction line next to the DC into a bucket of water. Turn the single and double DC on and measure the inches of water picked up in the tube (note run to ceiling then down) The inches of water is your suction pressure.

The performance change of two DC is dependant on the pipe too. If your piping was 4' long and open ended on the suction side, you'd pretty much get double the flow. 1000' of flex hose and you probably wouldn't be able to measure the difference. The reason piping matters, it affects where on the curve you are operating with 1 DC, so the effect of adding a second DC is different.


edit
Per Wiki answers since I didn't have a fluids book handy - Change in pressure is proportional to the square root of the change in velocity. In english, double your suction pressure head, and you get square root of two time the original flow rate, or 1.414x original flow rate. I'll see if anyone knows anything about fan curves at work.
 
Last edited:
Another much easier thought - I think wood magazine has a DC guru on their forums. There' a decent chance he either already has answered this, or is familiar enough with the fans to answer it off the top of his head.
 
Here's a couple articles that give some examples and actual dust collector performance curves:

The system flow rate vs pressure:
http://www.dshayairsystems.com/Design Notes/Fan Laws System Curves.pdf

And some actual published dust collector curves
http://www.oneida-air.com/documents/AWW article jan 2006.pdf


In the higher flow regions, 1000+cfm for these dust collectors where the slope is closer to horizontal, you should see close to 50-75% increase in flow rates with two collectors. At the lower flow regions, where the slope is closer to vertical you will see a very minimal change. It's reasonable to expect a similar shaped curve on the inside of these curves for say a 1hp dust collector.

Also, the suction pressure is less than I thought, just a few inches of water. Measuring this would let you know where on the curve you are operating.
 
Larry I just did some searching on the other forum and I keep seeing that they recomend that they be connected in series and not parrallel. Output of one to the input of the other.
 
yur just tryun to make i t rough on me arent yu:) alan now its gonna take up more room to go piggy back..looks like the hand over hand idea of unlading a truck which in my head is silly everybody has to handle ever bag instead of a portion of them..
 
I don't know what to tell you about that Larry. This info I read comes from the two dust collection guru's over there. Maybe it's sort of similar to a two stage compressor. One cylinder pumps in to another cylinder then into the tank. Maybe some experimentation is in order here.
 
Certainly would want to move more air. Are you talking in tandom or in line with eath other, Works like a pair of batteries... Series connection ups the voltage but not the power, parrallel hookup keeps the same voltage but boosts power. The capacity of the duct would restrict the volume of air being moved. If you are already working at capacity then there would be no improvement. If you increased the capacity of the duct, it would allow mor air but spreads it out so the volume of movement will stay the same, sorta.
 
We tried tuning a VFD fan at the mill before the ductwork was connected and found that the fan kicked out at 80% speed. We were pumping more air thatn would be allowed with the ductwork connected.

This is important when balancing a dual fan system. If you increase the duct size for two fans, they need to be in some balance for flow from each fan.
 
I'm no expert on this stuff, so take my opinions (cause that is all they are) with a grain of salt, I could be very wrong.

I have done a lot of reading on the subject and I've built my own cyclone from scratch, for whatever that is worth.

I do not think you will see any significant increase in performance.

Static pressure counts for next to nothing in a DC, Cubic Feet per Minute, CFM and Feet Per Minute FPM to show the speed of the air. In a vacuum system, like a shot vac, the static pressure is important, but in a DC system, the CFM is king.

I am fairly sure that hooking up two smaller DCs does not really give you any advantage. What scientific method have I used to come to this conclusion? None, that is not my area of expertise, but, I think if this did work then why is everyone not doing it? You can often pick up cheap 1 HP units on sale, so why don't guys buy three or four and hook them all up? :dunno:

Honestly, if this worked, don't you think all the DIYers out there would have done it, and shown it worked and be using this cheap and simple cheat? :D

The fact that now one does this, well that weighs very heavy in my thinking that it would not work. :(

The more I think of this, the more I think it is a bad idea. :bang:

Blowers work by compressing the air, moving it faster, and to do this you need power, the more air moved the more amperage drawn, the better , more powerful motor you need.

Do this simple test, if you have an amp meter around hook it up to you DC's motor, now remove the hose from the intake and block it off, and remove the hose from the filter side and block that off too. Now no air gets into the blower, you will find that the amperage drawn is low, as there is no work to do, the motor and the impeller just putt along. Next remove the blockage and try the test again, with no restriction on the intake or the filter side.......

but try it only for a second or two and at your own risk, with the motor running the impeller in the blower with no restriction

With all the air it can churn, the amperage reading will go way, WAY up, as the motor works harder having a lot of air to move......

you can quickly burn out a motor doing this so you have been warned, be careful, don't come crying to me because you let the smoke out of your motor :eek::eek::eek: :doh:

Now if you put two blowers in series, as suggested above to the first blower is in effect super charging the air stream for the second blower, and you will almost certainly burn the motor out in the second cheap blower set up. I would say it would work, but you would need a really powerful motor to handle the super charged stream of air from the first motor, and this would end up costing you more money than just simply buying the 5hp Leeson motor and 14" impeller you need to make a blower that moves enough CFM to catch all the fine deadly dust.

Hooking them up in parallel, as mentioned above, would not give you an increase in CFM, like hooking up two batteries in parallel, your voltage does not increase.

If you have two DCs you would be better off splitting up your work between them, maybe making one that is dedicated to only your planer and jointer or some such set up, that might work better for you.

I hope this helps, it is only my thoughts and opinions, I have only that to fall back on. :wave:
 
From what i have read I would vote to agree with what Stu has said.

The hardest think to grasp in the DC business is the difference between the vacuum we have with a shop vac and the concept of moving air in ducts to move dust.

Thats been my experience. One needs to get a grip on the concept of Static pressure.

I say with all the members you have in Mi around you, Paul, Steve, Tom and Jonathan, you should have a cyclone building day and put them to work. There is enough collective talent there to nock out anything quickly if you provide the barley hops.

Then go for a kick ass motor and voila problem solved.

Of course i cannot remember the size of the duct lines you have run in your shop but if they 4 inches you got certain realistic limitations there as to what you gonna get in air movement.

Dump the two and use the proceeds to fund making your own big one. Think of the space saving too.:D
 
I say with all the members you have in Mi around you, Paul, Steve, Tom and Jonathan, you should have a cyclone building day and put them to work. There is enough collective talent there to nock out anything quickly if you provide the barley hops.

....or screw it up....
 
thanks stu for some more logic...the fact that no one else has done it and braged makes alot of sence.. i knew i wasnt a genius inventor but it looked doable:dunno: and no i hadnt been partaking when the thought came to me..
 
Top