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.
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?
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.
