Upgrading a Small Dust Collector

Detailed advice on beefing up the capacity of a dust collection system in a small shop. September 24, 2006

I have a small shop (30x30) and a 1.5 horse Delta single stage dust collector. I mainly used it for my table saw with 4" pipe and it has worked fine. I just ran flexible hose to three locations along my work areas and to my miter saw and one floor sweep, all with 4" flexible pipe. I also added a 44 gallon garbage can with a pre-made top which works like a cyclone filtering out larger stuff in the garbage can before going through the fan/filter. I have the one filter bag on top and a plastic waste bag that the dust settles in. Do you see any problems with this setup or ways that I can improve without a lot of cost? As it is now, I can not use more than one collection system at a time. Is this normal? Also, would I improve my suction much if I went with two filter bags (one on top and also one on the bottom instead of the plastic bag)? And is there an easy way to test the system for leaks, suction, etc? I don't know much about dust collection systems and want it as efficient as possible with my current resources.

Forum Responses
(Dust Collection and Safety Forum)
From contributor M:
I have a shop that is roughly the same size as yours and also started out with a small dust collector. I discovered that the smaller dust collectors are not suited for what you are trying to do (not enough cfm). I suggest saving your money, sell your small "chip collector" and buy a true cyclone; many companies now make a good one for the small shop... But do your research! Moreover, watch for deals on this website and eBay for a quality used one. Last, you can check for leaks by running your system and holding a candle under the duct joints; the smoke will get pulled into the poorly sealed joint.

From the original questioner:
Thanks for the response. What DC unit did you end up with and how much was it? Does running my current system through the retrofitted 2 stage (garbage can) deplete very much of the suction?

From contributor T:
Do you have single phase or three phase power? I have three used DC that I no longer use, but they are three phase motors.

I think that long runs of flexible hose will be cutting down the efficiency because of the corrugated surfaces inside. You would probably be better off with pipe. I tried a lot of solutions with a 2HP DC, which was all I could afford in the beginning. Some worked better than others.

The best was to make a plenum/main duct from particleboard. Rectangular or square, approximately 6x6 inside. It ran along the back of my bench where the majority of the tools were located, so it was about 16 feet long. I contact cemented and screwed aluminum flashing to the inside before assembly to ground the system.

Then I cut holes in the front of the plenum/main duct for waste gates near each tool. The DC was at one end of the plen/main duct. The DC I had (Jet, I think) had a rectangular intake when the adaptor for hose was removed. The plen/main duct was about the size of that intake. I think it worked because the inside was pretty smooth, and the air had a straight shot from the waste gates into the collector, and the flex hose from the waste gates to each tool was pretty short.

The table saw was the worst performing, because it had the longest ductwork (straight 4" round along floor and up to the plenum). But I still can't get 100% from my tablesaws with a 7.5 hp cyclone!

From contributor M:
I have an Onieda cyclone (2 hp) and it does a good job, however I would at some point like to move up to a bigger one. Contributor T makes a great point about not having too big of a cyclone for his purposes. Obviously you can oversize your dc in conjunction to your duct runs/setup, etc. The Oneida people are great at helping you design a well-balanced system, should you decide to do a major upgrade (duct runs and cyclone). I personally would sell things on eBay in order to afford this jump in shop efficiency, because my dc system is used more than any other tool in my shop. Last, contributor T's other comments are right on the mark! I hope things work out for you.

From contributor B:
From what I gather, your dc is a Delta model 850, 1 1/2hp. There is some upgrade potential with that dc. Much more so than many others in this class. That's primarily due to the size of the blower outlet duct, which is 6". Typically, those 1 1/2hp dc's use a 5" blower outlet between the blower and bagtree.

There have been several versions of the DC-850. Some have included a 12" impeller. If you have that 12" impeller, you'll get a dramatic improvement in flow, simply by adding a second filter-bag. There are several ways to go about this. Be forewarned, however. Increasing airflow dramatically will result in a surge in required horsepower, which could overwhelm the small motor, unless you provide proper restriction. That restriction will come in the form of your ducting. That's where it *should* be. Running the free-breathing dc, unrestricted, say with a very short, large diameter duct, might cause overheating. Fortunately, that dc has manual thermal overload protection.

Now, in order to gain from the modification, you'll have to upgrade your ducting to 6" diameter. That dc has a 6" intake. Remove the twin 4" wye at the inlet, and hook up your 6" pipe. Downstream, it's perfectly fine to have a 6" drop splitting to two 4" ducts to serve smaller machines like a router-table, etc. or 4" to a saw's base, and another 4" to an overarm blade-cover. Those two 4" ducts will feed roughly the same amount of air as a single 6" pipe. Don't close one of the 4" ducts. That will reduce flow in the 6" main.

One important detail. Behind the 6" blower intake, some versions of the dc-850 have a 5" restrictor collar. That is simply tack-welded in place. It is used to restrict airflow, in case the user doesn't provide enough ducting restriction. Remove that collar, otherwise you won't be able to use your 6" pipe effectively.

The motor can be wired 110v, or 220 v. I'd go with the 220v and a proper circuit provided for that.

There are many ways to configure the twin filters. Replacing the lower plastic bag with a filter-bag is the easiest. You could also mount both filters to the top of the dc, and keep the plastic lower bag. In order to do that, you'd have to make a plenum.

That plenum would be a simple box with a hole cut out of the bottom, and mounted where your present filter is mounted. In the top of the box, cut out two holes, and mount both filters there, side-by-side. You'll need to make some filter mounting flanges.

Shop size won't necessarily dictate what size dc you need. You have to consider which is your most demanding branch in your duct network. Then you choose a dc capable of handling that demand. In your case, you're probably only operating one machine at a time.

Moving more air is one thing. Providing enough static pressure capability (suction) is quite another. The longer your duct network, the more static pressure resistance you're adding. Further, adding elbows also increases resistance. Keep your ducting efficient with a small dc like this. Use a minimal amount of elbows, and try to use 45's wherever possible, rather than 90 degree. Long-radius elbows are better than tight radius, etc.

Another gain might come by keeping your main duct close to the floor, at blower-intake level. This will avoid vertical drops that require 4000 fpm velocity for appropriate particle suspension. In a horizontal main, you only need 3500 fpm. That can be achieved in a 6" pipe, with as little as 685 cfm flowing through the 6" pipe. If you use vertical drops, your dc has to be able to pull close to 800 cfm in order to get that 4000fpm velocity.

Total cost of modification = 1 filterbag. Roughly $50. Go with 1 micron filters. If you add a plenum made from hardboard, perhaps another $15.

From the original questioner:
Thank you so much for the response. Extremely helpful. Could you please explain what a plenum is? Is it something that I would make or is it something I would buy?

From contributor B:
A plenum is merely an air chamber. Instead of mounting a top filterbag, mount a plenum. Then, mount the filters on top of the plenum, side-by-side. It doesn't have to be particularly strong or sturdy, just air-tight. You could easily make one from a sheet of 1/8" hardboard. That only costs about $10/sheet.

Picture a rectangular box, maybe 8" tall by 22" wide by 44" long. That would allow you to mount two 20" diameter filters side-by-side on top of the plenum. Of course, you'd need bag-mounting flanges, so if your filters are 20" diameter, cut two 17" diameter holes in the top of the plenum, and you can make flanges by using MDF rings. Maybe two layers thick (1/2" each). Make your rings 1 1/2" wide. Just enough to allow you to snugly slip your filters over the flanges, and add a filter clamp.

To save on MDF, instead of cutting full 20" circles, you can make half circles. Butt them together. Then for the second layer, just stagger the joint 90 degrees. If you want to save space, you can make the bottom hole of the plenum at one end of the plenum. That would allow you to have the plenum overhang the blower. You could even add a couple of legs to that overhanging plenum, going down to your dc's dolly. There are no serious weight or pressure issues. Very inexpensive to do, as well.

If that's not clear, let me know. Can you also confirm that it is the dc 850 that you have? Also, does it have the 6" intake?

From the original questioner:
Thanks again for the response. You are right on my D/C model. It does have a 6" intake. I have about 3 feet of 4" hose going from my DC to a drop container (garbage can). The top on the can that the hoses hook to is only for 4". If I went 6" from my D/C to the drop can and then reduced it to 4 so it would hook to my lid, and then increased to 6 again after, would I be limiting it? Would it be useless to use 6 if I reduced it to 4 for the drop bucket only? And if so, do you know of a way around that dilemma?

From contributor B:
I presume you're talking about a pre-separator lid that fits to the top of a garbage can. You most likely will find that you do not need it, depending on whether or not you decide to top-mount both filters to a plenum. All your waste will be collected in your lower plastic waste bag.

If you do decide to keep it (pre-sep), then you have to start thinking about replacing that lid with one that has a 6" or larger hook-up. You can easily make one using some inexpensive HVAC fittings. HVAC elbows only cost about $3 - $4 each.

You really shouldn't ever reduce the size (diameter) of your duct. This creates a massive pressure drop, and may reduce your draw by over 50%, and possibly more. It's okay to split a 6" duct to two 4" ducts using a wye, but you need to keep both of those 4" ducts open (no blast-gate) to feed the 6". Since two 4" pipes is roughly equal in area to a single 6" pipe (about 90% actually), you'll create little extra resistance, and you'll pull enough air to properly feed the 6" pipe.

Here's an example: Let's say your 6" pipe is pulling 800 cfm. Velocity through that pipe is roughly 4000fpm. That's ideal for wood waste. By reducing to 4", you're reducing the area of the duct by more than half. That same 800 cfm would have to travel at more than double the speed through that 4" restriction. That would create a massive increase in resistance. Much higher than if that same 800 cfm was traveling through the 6" pipe. Your dc will draw less air. In fact, you might now be pulling only 400 cfm. That 400 cfm is fine in the 4" pipe, since velocity will be high, but once that 400cfm reaches the 6" portion of the duct air-speed will drop by half, to roughly 2000fpm. That will lead to clogging in the main duct.

On a small dc like yours, there is not much room for static pressure loss. Total static pressure capability of the blower might only be 8"-9" WC. You have to keep the resistance low, by providing the proper sized ducting, and using as few twists and bends as possible. Always use 45 degree take-offs in your ducting if possible, instead of 90 degree, etc.

Remember, dc's are "air movers." They don't operate like a shop vacuum. Suction is nowhere near as strong in a dc. A small Fein shop-vac can provide up to 100" WC of suction, which would be 11-12 times higher than your dc. Dc's have to breathe freely.

If you decide to do the blower modification (removing 5" restrictor, behind 6" intake), then just replace that plastic lower bag with the 1 micron filter-bag. Try it out. Use a length of 6" pipe to the intake. You'll be astonished.
If you want to use your pre-separator with a 6" lid outlet, do so, and simply leave your dc alone. Don't bother making the plenum to top-mount both filters. Later, once you've ducted the dc to your machines, you may find that you have plenty of suction. If that is the case, and you'd like to use the lower plastic waste bag, then you can add the plenum, with the two top-mounted filters. The pre-separator will add a little resistance. Also, you may have to tweak it to get ideal pre-separation. You may find that with the increased air capability, your dc sucks the pre-separator clean.