Combining Dust Collectors

      Pros discuss using multiple blower setups for power and flexibility. May 10, 2005

Question
Is it possible to combine 2 blowers to get the CFM requirement you need? I want to combine two blowers with a 9" inlet into a 12" main.

Forum Responses
(Cabinetmaking Forum)
From contributor B:
I don't see why it won't work. Seems like you would need to run both blowers at the same time. My guess is that you already own two blowers and need more power. I have five smaller collectors in my shop split up on single machines. In this way, I don't run one big blower when I am only running one machine.



From contributor T:
I have about ten 2 hp collectors situated on a mezzanine. Each one of them drives just one machine. Most of them have custom felt air filtration bags from American Felt & Fabric. I have contemplated hooking them up to a common collection center, similar to a Dustek with air filtration on the top and plastic bags on the bottom. Right now the dedicated system works really well. We successfully evacuate a 20 inch jointer with about 45 feet of six inch pipe. Three quarters of that run is either straight up vertical or 45 degree incline. The overall hike vertically is about 12 feet.

I prefer to run the smaller collectors because it doesn't make sense to me to turn on 20HP of collector to run a 2 hp saw. Under my proposed scenario, each collector would still be dedicated to one machine. My (uncorroborated) theory is that each machine would become more efficient because of enhanced (shared) air filtration. I discussed this once before on the DC forum and someone suggested that I might need to introduce some kind of one-way baffle to keep back pressure from pushing dust toward the machines that weren't under power. Do you think it would work?



From contributor O:
To the original questioner: I've kinda been toying with a similar idea, only on a smaller scale. We are soon moving into a new building and we have a 2hp dc hooked up to most of our machines that exhaust into an outside dust wagon via a 6" outlet. We will be adding a couple more machines and I would like to purchase another 2 or 3 hp collector and hook part of the machines to one and the rest to the other and "Y" both 6" outlets into one, then out into the dust bin. Will this work or will I get blowback from one when the other is not on? If so, a baffle seems like a good idea. Any suggestions on fabricating one?


From contributor S:
Contributor T, think of it a s a plumbing problem. Subtract the fans for pumps and air for water. Without a one-way system after each pump, water would be forced into the pump from its pressure side (dust from saw 1 comes out at saw 2). Then also, what if two pumps were running at the same time? Would the pressure in the pipe be double or the same? And can the pumps work efficiently with existing pressure in the line? Pump 1 is running and therefore the pipe is pressurized. Pump 2 is not designed to work with the pressure that is already in the pipe, so it might cause pump 1 and 2 to work at the same output together as they would if operated on their own. Just some thoughts that jumped into my head while looking at your plan. Iím no expert, so I might be way off.


From contributor T:
Those are good points to think about. The back pressure can be fixed (I think) with the one-way baffle. I know enough about air flow to understand that it is complicated. (I see this in the diagrams where they postulate hypothetical air demand on shop layout.) This is why I started initially with one machine, one collector. I might experiment with this on a small case. Maybe just hook up three bags and two collectors. It would be really nifty if it worked. Lots of pull, low electrical consumption.


From contributor D:
The only way this would have any chance of working would be to run the collectors in series (one behind the other). The only problem you have is that the blower on the back side will be trying to draw too much vacuum and will burn out the motor. The only way to keep the back end blower motor from burning up would be to reduce the inlet size, which would reduce the cfm. Your best bet is to get a central system with one motor and one collection point. While you might save a few pennies on electricity, you will spend money on labor to keep emptying bags all the time. We have a large central system outside of our small shop and we spend 15 minutes once a month to clean it out. You can find inexpensive used systems on IRSauctions and Ebay.


From the original questioner:
You're absolutely right. I've seen huge collectors go from a few hundred to only a few thousand dollars. My problem is I don't have the 15-20k to spend on dust pipe at the moment. That'll end up costing way more than the system. The only reason I was considering this is because I have a few Bridgewood 5 HP collectors. They were only $949 ea, and I figured if I need 10HP, I'd combine them. I was looking at Dusteks, which are 3500 new, or maybe buying one of them at auction.


From contributor W:
We bought a used 10hp Dustek on www.IRSauction for $500. The trick is to use what you have and be willing to be patient and diligent. Keep looking until what you want comes up for the right price.


The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor C:
Using multiple dust collectors to power a dust collection system is certainly possible if you understand the advantages and the pitfalls. The assumption is, of course, that you have multiple machines wherein at any given time you may be running one, two, or more machines simultaneously. I empathize with your objective of not spending the money on the electricity to run a single large Hp collector when you are only running one machine because the cost of the electricity can be very significant.

Frankly, I would suggest you not look at this in the horsepower sense. For simplicity, let's say we are talking about two dust collectors. First, you do not want to run them in series as this would complicate the whole mess. You would have to modify the ductwork, and even so, you would likely be stressing the motor on the one unit - possibly beyond its design capability. So let's put aside the notion of running dust collectors in series or you will likely be burning out motors.

Again, forget about Hp for the moment and think air flow and vacuum level. For the sake of argument, we'll assume two 5 Hp collectors that you've indicated. I don't have data on the Bridgewood model so I'll use the data from the Grizzly catalog on their 5 Hp units.

I will also assume you are not using cyclone or vortex configurations. The system design would have to be totally different for this kind of configuration. (The heavy chips coming out of the cyclone fall under gravity force alone.)

Two units each are pulling a rated 3961 CFM with a static pressure of 14.6 inches of water. In a system with a main (larger) duct connecting both collectors and multiple machines these units will actually pull somewhere in the ballpark of 3,000 CFM each to be realistic. System leakage will increase air flow and reduce the vacuum.

Now, if you had one large collector you would have the problem of chips and dust falling back into branches of ductwork collecting at machines that are not in use and clogging these ducts. To prevent that you must use gates. These gates are located as close to the main duct as possible to prevent long lengths of ductwork filling with chips.

You have the exact same issue whether you are using one or multiple collectors. When you have a single system you must cut off the unused machines with gates in the ductwork. However, if you have the flexibility to do the following, gates at every junction can be avoided - assuming the large main line is run up near the ceiling. Run the individual smaller ducts from each machine up and slightly above the main duct so that the connection point is on top of the main duct. This will prevent gravity backflow of dust and chips into the branches - without the use of gates at every connection to the main duct. Of course, you will still have gates at the connection point to each machine - otherwise your system will have so much leakage as to require many times more Hp (to get the needed air flow) at the machine you are running.

Next, on the collector end you must devise some system for running the number of collectors needed for the number of machines running. Further, it's not just the number of machines, it's the air flow and vacuum level requirements for each. How big are your machines and what are the air flow requirements for each? That is what you need to pay attention to. For example, I'm running a 24" planer, a 24" sander, a 12" jointer, and a 19" band saw. For this equipment (all 3 ph with a collective Hp of 40 Hp) my 5 Hp dust collector is overkill if I want to run any two of them at the same time. Admittedly, I do have a tight system. My biggest problem is hauling away the amount of chips collected from the cyclone per hour. Especially when using the planer I fill a 55 gal drum in about 20 to 30 minutes.

Remember, you want all of the air flow coming from the machine or machines your are actually running. Running two collectors side by side should not be an issue if you set up the ductwork sized for the job. Furthermore, balancing the workload will be easy because you will be able to readily see if one of those collectors is harvesting more chips than the other.



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