Dust Collection - my latest two cents worth

[David Less]

Dan,

I have the same problem you have, trying to squeeze in a "good" cyclone. I've been through the Onieda stage and Chinese made stage as well as considering cutting a hole in my floor for room.
After talking to Ed from Clear Vue, he told me that if done correctly, I can mount the blower unit off to the side of the cyclone, thus saving valuable ceiling height with minimal performance loss. I'm now in the process of designing a stand the will allow the side mounting of the blower.

After running a HF 2 hp canister DC for about a year, I have come to realize the importance of good "dust to air separation", not to mention CFM from a quality unit. I've studied Bill's reseach several times again and have come to the conclusion that for any after market system to work well you need to be in the 3 1/2-5HP range and $1400 to $2000+ range for cost. Well, Clear Vue is less than $900 delivered.

Now, since I can get one of the best hobby cyclones to fit in my basement shop (with alittle stand design) for less than $900 delivered it makes the choices much easier for me.
My $.02

David

[Stu Ablett in Tokyo Japan]

Well guys I have to jump in here for a number of reasons, one is to thank Bill, again, for all his hard work!!

I built a "Pentz" design cyclone a little while back, and YES, it SUCKS!!

The seperation is unreal! I've gone through a fair bit of dust, once even filling my dust bin past capacity...... but I got lucky and stopped before I filled the filters!

I get so little dust in the filter stack clean out, it is almost non-existant!!

I still have some problems with the speed of my impeller (this is nothing to do with Mr. Pentz's design) but even though I'm not swinging my impeller at the best speed, it still works very well.

The other day, I was using the SCMS and I cut a board, just a short one, but I had not hit the cyclone switch (whoops!), I finished the cut, and then hit the switch, well the example of fine dust control could not be better. When I did the cut. there was a plume of fine dusts coming out of my SCMS surround, I hit the cyclone switch, and all that dust went whoosh into the ducting, and was gone!!

Sure, some of the heavier sawdust does not get picked up, but that is more of a design flaw in my surround and the hood, but the fine dust, well it has just about been banished from my shop.

You can see my Cyclone Saga <-- here

One last comment, and don't take this wrong guys, but if you benefit from Mr. Pentz's site, send the guy $5 for his hosting costs etc. I mean really, the price of a Tall Latte at Starbucks, and you can help out.

Just a plug there for Mr. Pentz.

Once you build a Cyclone, you will wonder why you waited so long, I sure did!!

Cheers!

[J.R. Rutter]

Hi Bill,

I really enjoy your posts, and web site, which I have followed since you put it up.

One comment on duct sizing. For shops than run multiple machines, duct sizing seems to be more important to balance air flow. I found that when I went from a 100% solo operation to having a helper a couple times a week, my 2 HP commercial blower and 6" drops to each machine wasn't cutting it. For this situation, it seems like a blend of traditional duct design and your well-taken pointers on maximizing air flow is called for? Adding a second open blast gate has a huge impact.

On another note, I wonder if you know how to calculate the maximun airflow through a given opening at a given pressure. I have a blower that was designed to evacuate a single aluminum billet saw and puch the chips and shreds up to a cyclone 40-50 feet away through 6" pipe. The outlet of the 10 HP blower is just 6.5" x 4", BUT the radial impellar is 19" x 4.75". My understanding of radial blower design is that wheel diameter sets max pressure, depth of fan sets max volume, but only so much air can physically move through a given opening.

I have set this up as a pull-through cyclone system, enlarging the blower inlet to 10", and using 2 Oneida filters on the outlet. Since I can't alter the blower outlet, this seems to be the limiting factor for me. Any thoughts on my max possible airflow?

[Cecil Arnold]

Okay Bill, you've sold me on saving my lungs, and the current deal from Clear Vue and your endorcement puts them in the lead. I do have a question about providing a return air from the DC enclosure. As you can surmise it's hot here and I am concerned about keeping as much conditioned air as possable in the shop. What size return will I need to return the max. 1800 cfm cleaned/filtered air without introducing pressure drop/back pressure problems? My current plan has the ability to include a 1x4'-1x6' return. Do you think that will be adiquite?

[Bill Pentz]

Dan,

Many have used my cyclone design in minimum height shops. My design has room to turn the top outlet ninety degrees and slip out in the dead air space under the air ramp next to the inlet. Because the outlet pipe is so large, making that tight turn costs little in terms of performance. Here is a picture and the dimensioned image. Forgive the perspective on the dimensioned side view, but the outlet does fit with only a small amount of deforming to work. It’s actually a little better to angle the outlet to exactly match the inlet then all fits perfectly.

Your other question is really unfair because you want me to make an evaluation that can seriously hurt Oneida-Air who has done so much for hobbyist dust collection and always treated me well. Every available hobbyist cyclone makes a good to great “chip collector” with Oneida-Air consistently being the best of this group. So the real question is what are my thoughts on the different fine dust collection abilities? Again, good fine dust collection requires upgraded hoods, larger tool ports, larger ducting, and moving a real 800 to 1000 CFM at each of our machines. Every hobbyist cyclone system that meets these conditions and gets put outside without returning the air makes a great fine dust collection system. Those that get put inside or return the air must also filter. Every hobbyist cyclone vendor except for WoodSucker and Clear Vue Cyclones now sells downsized agricultural cyclones for indoor use. Agricultural cyclones do a poor job of separating enough dust to return the air through filters. Even heavily modified as recommended on my Cyclone Modification pages , these types of cyclones do a poor job of separating the fine dust plus have too much overhead for indoor use. When brought indoors, agricultural cyclones make terrible fine dust collectors because:

1. Their design puts nearly 100% of the fine dust into our filters versus a design like mine that drops almost all of the fine dust into the dust bin. Installing all of the tested modifications still puts about a third of the fine airborne dust into the filters. Rapidly plugging our filters kills the airflow needed for good fine dust collection. Worse, cleaning our expensive filters is an unpleasant often unhealthy chore that rapidly wears them out.
   
2. Their internal design uses massive amounts of turbulence to break the airborne dust from the heavier particles so that airborne dust can be blown away outside. Creating this turbulence in a hobbyist sized cyclone is expensive, roughly 1 hp of blower overhead that instead of moving air to collect fine dust gets used up creating a maelstrom inside the cyclone.
   
   Some use a “neutral vane” to reduce this overhead to about 1/2 hp. Others use a partial air ramp that actually makes matters worse than if they had left it out. Regardless, this overhead leaves a 2 hp cyclone of this type a great “chip collector” but unable to move enough air for good fine dust collection. We know the overhead with neutral vane requires a 3 hp motor turning a 14” diameter impeller to move 800 CFM at the overhead for a small shop. Medium and larger shops along with those who live at higher altitudes like Denver, the mile-high city, need a minimum of a 5 hp motor turning a 15” impeller.
   
3. Agricultural cyclone designs are optimized to drop heavier chips and blow the fine dust out the top. These designs are notorious for sucking the fine dust right out of our collection barrels as those barrels get too full, any small air leak develops, or whenever airflow gets restricted from plugged filters or ducting.
   
4. Agricultural cyclone designs use a ratio of components that are easily shipped via normal carriers. The much longer cone lengths needed for good fine dust separation require use of a much bigger blower or much taller cyclone. Most hobbyist vendors choose the solution that is most inexpensively shipped and these solutions do a poor job of removing the fine dust, so end up reliant on their filters for most fine dust removal. Getting away from the agricultural cyclones requires different ratios and components:
   
   
   1. The cyclone upper cylinder diameter must increase as motor size decrease or we have a serious resistance problem that kills airflow. Using the university cyclone sizing spread sheets shows we need a cyclone diameter of 24” for up to a 1.5 hp unit, 22” for up to a 2 hp unit, 20” for up to a 3 hp unit, and 18” for up to a 5 hp unit.
      
   2. Using the swirl tube equations that govern all cyclone operation in combination with fine dust particle density (size/weight) we can compute the optimum airspeeds and dimensions for our hobbyist cyclones. Our hobbyist cyclones should be 13.5” in diameter and stand 54” tall for ideal separation and be powered by at least 7.5 hp motors turning 16” or larger diameter impellers. To leave those industry standards behind and come up with a design that can do the same job with a 3 hp motor took lots of work to develop a laminar flow using aircraft wing theory (I started my engineering schooling as an aeronautical engineer/rocket scientist). In addition to reworking the internal flows, I also had to experiment to make the compromises so we could fit the result in our typical 8’ tall hobbyist shop work areas.
      
   3. The blower outlet should be the same size or bigger than the cyclone inlet to prevent an airflow killing constriction?
      
   4. The cyclone inlet should match the supported ducting which means 6” in almost all cases with less than a 5 hp motor in which case we go to 7” to maintain ample duct airspeed.
      
   5. The cyclone outlet should be the same size as the inlet or it will either cause plugging or suck fine dust from the collection bin. The collection bin also should be metal to avoid fires.
   
   
5. In addition to pumping almost all of the finest dust into their filters, almost every hobbyist cyclone and dust collector vendor offers filters with one or more serious problems. The American Society of Heating, Refrigeration, and Air-conditioning Engineers (ASHRAE), is a non-profit group of air engineers who set the standards and certifies laboratories to provide filter testing. A certified filter test gives the filtering level and required filter area for a specific airflow with a particular particle loading:
   
   
   1. Almost all hobbyist dust collector and cyclone filters are uncertified. Every hobbyist dust collector and cyclone filter I tested freely passed particles ten to thirty times larger than their advertised filtering levels. Meeting government minimum air quality standards requires 0.5-micron certified filters. Those with allergies and other respiratory problems are advised to use 0.2-micron certified filters.
      
   2. Most supplied hobbyist dust collector and cyclone filters fall far short of the 1 square foot of filter area for every 2 CFM used for filtering relatively clean air that has already gone through a cyclone separator. We need at least 400 square feet of filter area for an 800 CFM air flow to avoid constant filter cleaning. Not only do most hobbyist cyclones pump too much dust into the filters, undersized filters rapidly plug killing the needed airflow for good fine dust collection and creating a messy cleaning chore that rapidly wears out our expensive filters.
      
   3. Many use all paper filters that quickly break down with cleaning leaving them useless for fine dust collection.

bill

[Bill Pentz]

JR, Stu, et al,

Thanks for the kind words..

bill

[Bill Pentz]

JR,

If you want the fine dust you need to move 800 CFM at most larger machines, adding a second open gate for an identically sized run splits the airflow in half. Runs of different sizes require significant balancing to ensure the larger does not leave the smaller with little to no airflow. That kind of balancing as Allan has said takes some work and exceeds what should be discussed here.

If you look at the fan curves for most hobbyist cyclones the 2 hp barely move 800 CFM at the minimal 7” of ducting resistance in most average shops and barely move enough air for good chip collection when you add the overhead of filters and an agricultural cyclone. Stepping up to a 3 hp just barely provides the needed 800 CFM. We know we need a real 450 CFM for good chip collection, so splitting our 800 CFM into to two roughly 400 CFM airflows works but leaves us a little shy for chip collection and about half the air needed for good fine dust collection.

You are exactly right in saying "duct sizing seems to be more important to balance air flow". For instance, the reason I keep harping on no smaller down drops is an 800 CFM airflow in a 6" pipe gets killed by just 40" of 4" pipe to only 349 CFM. Smaller ports are not quite as bad but really do make a huge difference depending upon size.

The Fan Law formulas with a little algebra let us calculate the expected behavior for most airflow situations. You can use these formulas to compute just about anything from pressure drop to expected performance changes with varying impeller size:

1. FPM varies CFM divided by duct area: FPM = CFM / Area measured in square feet.
   
2. CFM varies Directly with RPM: (CFM1 / CFM2 = RPM1 / RPM2)
   
3. SP varies with the SQUARE of the RPM: (SP1 / SP2) = (RPM1 / RPM2)^2
   
4. HP varies with the CUBE of the RPM: (HP1 / HP2 = (RPM1 / RPM2)^3
   
5. Noise volume changes with speed: N2 = N1 + 50log10 * (RPM2 /RPM1)
   

The amount of air moved depends upon pressure generated. In simple terms a pressure blower works by slinging the heavier air off the impeller blades. The more air sent away the higher the volume and higher the pressure. Adding a top ring to a blower impeller to turn it into a caged impeller and spinning it much faster is exactly the difference between a shop vacuum and a blower. Clearly blade height, shape, impeller width, rotation speed, blower housing, blower inlet design, and blower outlet design all come into play in defining how much total air gets moved at what pressure.

Your big blower designed to move metal chips needs more suction than a typical dust collector or cyclone, plus must move the air faster in the ducts to ensure the material stays entrained, meaning kept airborne. I recommend study of the Study of the Cincinnati Fan Pressure Blower PDF Pages for more information. In fact, most hobbyists would be well off to carefully read and understand these pages because it is our chore, not our vendors to come up with dust collection blowers ample to power our shops.

Enlarging the blower inlets and outlets without carefully protecting the blower from trying to move too much air with restrictive ducting is a recipe for disaster. Our blower motors do the most work when they move the most air. Giving them too much air by opening all up too much

bill

[Bill Pentz]

Cecil,

A big enough air return should minimize having the air compress because any compression will steal blower horsepower. If you use a filter box that pushes the air through the outside to the center of your filters, then the inlet going back to your shop should be as big as the outlet from that box, typically 8” to 12”. If you use my recommended filter setup you release the air from the entire area of your filters so unless you put the filters in your shop will compress the air a little to put it through a smaller opening. Bigger is better.

bill

[Allan Johanson]

The topic of multiple drops is a tough one for many folks to understand and it applies in the case mentioned above with two people using machines at once as well as a single tool operating with two drops like a tablesaw with one drop going to the base and another to an overhead guard.

I'll attempt to clarify this a bit with a shop-tested example.

For those folks whose eyes haven't glazed over at the mention of static pressure loss (SP) in duct runs, here's what happens with multiple drops to a tablesaw (just an example):

The SP loss in each of the branches will equal out to be the same value. Since the "resistance" (as I call it) is the same for each branch above and below the tablesaw top, what happens is the airflow goes up or down in each branch to balance the resistance.

You've heard that higher airflow in ducting can raise the resistance in the ducting, and lowering the airflow will reduce it. Well, the same thing happens here - just another layer of it.

The shop-tested example:

7" main duct for a while, then branching off into two drops.
6" to the base of the saw (about 10' of 6" pipe and 10' of 6" flex)
4" to the overhead guard (about 4' of 4" pipe and 12' of 4" flex)

I set up my test case where I had Dwyer-approved lengths of straight ducting in each branch so I could take my measurements.

airflow in 6" branch: 850 cfm
airflow in 4" branch: 285 cfm

************

All right....now let's play around and dramatically reduce the resistance of the 6" ducting by removing most of it. So I now had my 7" main duct branching into 6" and 4" drops with the 4" branch going to the overhead guard and the 6" drop was running through a length of straight pipe and then in the open air.

The entire 6" branch was now about 5' long. The 4" branch was the same as before.

What happened?

If we think about it for a minute, the 4" branch had an obvious potentially high level of resistance due to all that ducting and the 6" obviously didn't. How is it going to balance out?

By increasing the airflow in the 6" ducting and dropping the airflow in the 4" ducting.

The test results:

airflow in 6" branch: 1205 cfm
airflow in 4" branch: 215 cfm

********

Not only did the lower overall resistance increase the total airflow in the main duct by almost 300cfm, but the low resistance in the 6" ducting allowed it to flow much more air and it cannibalized the airflow from the 4" duct since that drop lost 25% of its airflow.

*******

If you will be using multiple drops (or multiple tools), and if you are concerned about maximum performance, you really need to consider balancing out the airflow. This isn't only about duct size and length, it's also about hood design/placement and about the particular brand of tool. Some are very restrictive and if you don't know how restrictive the tools are themselves, then you might have poor performance.

If it's a critical situation for you, then you might want to get someone in to properly balance your shop and set things up for you. That's beyond the scope of these forums.

Cheers,

Allan

[Bill Pentz]

Allan,

Sharing the testing of your system is a huge help. I often end up feeling like the one in far right field all by myself. Thanks!

bill

[Dan Forman]

David---With the new stand, what is the minimum required ceiling height for the clear view cyclone?

Dan

[Jim O'Dell]

Dan, I just went and looked at Ed's site, and I don't see the page that had a line art drawing of the cyclone with lengths listed, but IF I remember correctly, using a standard 33 gallon metal trash can for the chip/dust collection, it will fit under an 8' ceiling. Hopefully someone else will drop a note to be sure. If not, I know I have a printed copy of the page I can't find out in the shop, I'll go find it. Jim.

[Jim O'Dell]

Well, I just went out and looked...can't find said piece of paper! I measured mine...75" from the top of the motor to the bottom of the flex hose that goes to the trash can. That leaves 22" or so for the can. My metal trash can is 23 1/2" tall. BUT!!! The flex hose at the bottom of the cyclone is a good 5 to 6", so it should fit under an 8' ceiling fine. Jim.

[Dan Forman]

Jim---Thanks for measuring, unfortunately my ceiling is just under 7' to the bottom of the joists, with an additional 9" between the joists. According to the Clear Vue site, I would need 8' of space allowing 29" from the bottom of the seperator to the floor. With a 23" can and 3" of flex hose, looks like the motor would still be hitting the ceiling (93"). I know that Oneida recommends at least two inches of clearance under a ceiling to allow the motor to breathe.

Bill or David---Are you saying that the motor and impeller can be mounted to the side of the seperator in a way that would let me use this within my height restriction?

Incidentally, something seems to be up at the Oneida site, There is no info available now for either of the 2 HP Gorilla systems. They just say "coming soon"

Dan

Dan

[Jim O'Dell]

Jim---Thanks for measuring, unfortunately my ceiling is just under 7' to the bottom of the joists, with an additional 9" between the joists.
snip
Dan

Ouch! And I thought my shop ceilings at 7'9" was low. You must be in a basement?? Let's see what the others have to say about separating the blower. Maybe if it was turned 90 degrees to the cyclone and some gentle radius piping used, it would still work well.
Bill P., what would tilting the whole ensemble say 30 or 40 degrees do to the operation of the cyclone? That might gain some space. Jim.