Dust Collection - my latest two cents worth

[Bill Pentz]

Emails this morning scolded me for not posting this as a new thread, plus leaving a few things off. Here is an updated version of what I shared at the end of the last cyclone thread. bill

Making a dust collection decision requires you to first decide on what it is you want to do. If you just want a shop with no chips, then just about any hobbyist 1.5 hp or larger dust collector or cyclone will work well for you because you only need about 450 CFM airflow for chip collection. If you seriously want to get the airborne fine dust in your shop under control then you have a whole different set of concerns. You can go to my web pages and study for yourself the dangers of fine dust and what it takes to control, collect and get rid of it.

Many local safety standards require putting commercial cyclones and dust collectors outside. That works well because these outside units let the fine dust blow away outdoors. For hobbyists, exhausting outside is illegal in many areas. It can be hard on the pocketbook to send our heated and cooled air outside and our air conditioning equipment will mostly not keep up. The noise and debris can upset neighbors. Some types of chips and dust kill plants. Blowing our shop air outside can also suck deadly carbon monoxide backward through the vents on our heaters, stoves, water heaters, and other fired appliances into our shop air. Putting these units outside also often requires making them a special enclosure. Many hobbyists choose to just bring these outdoor units inside.

When hobbyist started bringing these downscaled commercial dust collectors, cyclones, and small shop vacuums inside it created a serious hidden problem. These smaller units make great “chip collectors” that will leave our shops spotlessly clean except for a coating of the unhealthiest finest dust on everything. That coating comes from moving too little air to gather the fine dust as it is made and too open filters that blow the finest unhealthiest dust right through. Unlike commercial firms that blow this fine dust away outside, hobbyists trap the dust inside. This fine dust builds and lingers for months getting even more dangerous as molds, mildew, and fungus break it down. Our tools and even dust collection systems become “dust pumps” that recycle previously made dust. Government testing of hobbyist shops that turn professional shows most end up with fine airborne dust levels over ten thousand times greater than permitted in commercial facilities. We as hobbyists often receive more fine dust exposure in a few hours of dusty woodworking than a commercial woodworker will get in a year.

With almost no hobbyist tools, dust collectors, cyclones or ducting setup for anything but "chip collection" getting good fine dust collection takes a lot of work. We have to remake most of our tool hoods and tool ports. We need a good downdraft table and portable dust collection hood. We need a much bigger blower that moves a real 800 to 1000 CFM at each major tool. We need larger lower resistance ducting than most hobbyists vendors sell and cannot use commercial ducting designs because the smaller down drops kill the airflow in our mains building up dust piles. These piles pose a fire hazard and will eventually ruin our impellers, motor bearings, and filters from breaking loose and slamming around. We also need to either exhaust the dusty air outside or run it through fine filters.

We can't just run the dusty air through a filter. Meeting government commercial air quality standards that many now think are not tight enough requires filtering all particles down to 0.5-microns in size. My doctor and many other health professionals recommend filtering down to 0.2-microns. We also must have enough surface area so the filters do not plug too quickly and kill the airflow needed for good fine dust collection. Most can only provide enough filter surface area by using large cartridge filters. Fast moving wood chips quickly plug and punch holes in cartridge filters as too many are now finding with their cartridge dust collectors. Cleaning rapidly also wears holes in these expensive cartridges.

Protecting these filters can be done with a drop box, meaning a huge pipe with so much area that the airflow drops below what will keep the chips entrained (kept airborne), or using a cyclone separator. Trashcan lid separators are a type of drop box that many hobbyists find work well for “chip collection”. Unfortunately, the higher 800 to 1000 CFM airflows needed for good fine dust collection scour the cans clean unless the trashcan separators become huge. Most find a 5’2” diameter seven foot tall or larger trashcan separator too big, so instead turn to cyclones for separation.

The huge cyclones we see outside most large commercial woodworking facilities are agricultural cyclone designs that work well. They provide almost exactly the same 85% separation efficiency by weight that our far less expensive trashcan separator lids provide for “chip collection”. These cyclones were designed to separate dirt and sand from cotton. They use very high internal turbulence to smash the dirt and sand loose from the cotton fiber. After breaking the heavier stuff loose it gets slung by spinning air off to the cyclone sides and gravity pulls it into a collection bin. Close to 100% of the fine cotton fiber blows right out the top of the cyclone. When used for woodworking, high internal turbulence smashes the fine dust from the heavier chips. Close to 100% of the heavier chips and sawdust drop into a bin and near 100% of the fine airborne dust away into the outside air.

Sadly hobbyist vendors discovered that if they feed their cyclones only large heavy chips, say from planers, they can advertise close to 100% separation efficiency for cyclones that provide 85% separation efficiency. Feeding these same cyclones all fine dust, say from MDF, puts close to 100% of the dust into the filters.

It is no secret that almost all hobbyist cyclones are downscaled copies of agricultural cyclone designs sold by Delta to small commercial shops for decades. These units require a 7.5 to 15 hp motor for the same sized cyclones that hobbyists try to power with 1.5 to 3 hp motors today. With lots of help we worked through countless design changes to improve these hobbyist agricultural cyclone separation efficiencies. We learned most hobbyist vendors did not know the cone on the bottom of the cyclone requires just the right shape and proportions to keep that heavier material from causing plugs or getting sucked back into the exiting air stream. We learned inlet size, shape, length, and angle is critical. We also learned that the incredibly high turbulence was not needed if we wanted to separate off all the dust. With clever modifications we got these cyclones from 85% efficient by weight to the low nineties.

That was just not good enough. In spite of adopting many of our recommended changes, hobbyist vendors continue to sell cyclones that require more time to fix than building a cyclone from scratch, plus cutting up a brand new unit just hurts too much. Hobbyist cyclones still constantly plug their undersized filters, pass much of the finest unhealthiest dust right through their too open filters, fail to move enough air for good fine dust collection, and fail to move enough air for good separation with anything less than 3 hp or larger motors.

Larry Adcock with his WoodSucker II design, my design plans available off my web pages for free, and cyclones based on my design sold by Clear Vue Cyclones made major steps forward. Larry used a more efficient caged impeller and I used an airfoil impeller. Both move 3 hp air volumes with a 2 hp motor. We also both got our separation efficiency up into the middle ninety percentile before filtering. My continued testing moved me away from the caged and airfoil impellers. They generate so little air pressure they only have enough power to collect from small shops plus they need regular cleaning. I refocused my design enhancements into building an overall more efficient cyclone and blower. Everyone who uses the result can attest to their air movement and separation efficiency.

Meanwhile, if you won’t use large enough ducting, upgrade your machine hoods, move enough air and use fine enough filters, just buy a good 1.5 to 2 hp dust collector and be happy, because your cyclone is not going to give what is needed for good fine dust collection.

bill

[George Robin]

Hello Bill,

As your website is, so are your posts.....full of valuable information.
Thank you.

Regards,
George

[Ed Lang]

I am unhappy to hear that you received negative email.


I am very happy you took your time to post at the thread I started, and again here.

In fact, after your post to my thread, I went back to your web site and started to read again. I liked the experiment with the small clear tube and breathing. I will pour through the information again this afternoon and this weekend. Maybe some folks think like I did... it is only dust. Seems mother nature has a way of removing those from the gene pool.

[Bob Marino]

Thanks Bill for this very usefull information and your tireless efforts in this area.

Bob

[John Stevens]

These smaller units make great “chip collectors” that will leave our shops spotlessly clean except for a coating of the unhealthiest finest dust on everything. [snip]

This fine dust builds and lingers for months getting even more dangerous as molds, mildew, and fungus break it down. [snip]

Government testing of hobbyist shops that turn professional shows most end up with fine airborne dust levels over ten thousand times greater than permitted in commercial facilities. [snip]

We as hobbyists often receive more fine dust exposure in a few hours of dusty woodworking than a commercial woodworker will get in a year. [snip]



Bill, it seems like you've done quite a bit of research in this area. I've done some searches on google and pubmed, but I guess I'm not good at framing search terms, because I came up with no references to reliable scientific sources of info on these issues. There are some books and magazine articles for hobbyists and small shop operators, but the ones I've read fail to cite the sources of their info. I've been on your web site a few times and was unable to find it there.

Would you mind posting your sources for this info? Thanks in advance.

[Bill Pentz]

John,

I used to keep many links to medical articles on my web pages, but keeping them up became overwhelming, so I now suggest people do their own searches. Finding about the health risks of fine wood dust is pretty easy. Just do a few Google searches (fine wood dust hazards (http://www.google.com/search?hl=en&q=fine+wood+dust+health+hazards)) and (PM 2.5 health hazards (http://www.google.com/search?hl=en&lr=&q=pM2.5+health+hazards&btnG=Search)). Reading and making sense of the better medical articles is not quite so easy, but still doable.

The second part of your question is the same one that threw me when I got started. I only did a little woodworking now and then and already used most of the best available in hobbyist dust collection with fine filter bags, so figured my exposure and risk was tiny. Yes, I ignored the coating of fine dust everywhere on my tools that also joined us inside our attached home. It was not until an OSHA inspector friend came over and educated me by showing with his test gear that I could believe the problem was so bad. Just turning on my cyclone with no woodworking at all raised the airborne dust levels in my shop thousands of times over allowable limits in commercial facilities. Do I have credible reference studies to back this up, no just my test results because nobody else has spent the time and money to do independent testing. Regardless, if you think about why this is a problem most don’t question these results:

Unlike commercial concerns that have long blown fine airborne dust outdoors, hobbyists keep the dust trapped indoors.
Our tools and hoods fail to control and protect the fine dust before it can spread.
Our dust collectors move too little air to capture the fine dust at the source.
Our small ducting will not support the airflow needed for good fine dust collection.
Our too open filters turn our cyclones, dust collectors, air cleaners, and shop vacuums into “dust pumps” that constantly blow the finest unhealthiest dust right through.
This dust builds and lingers for months getting cycled back into the air every time we turn on our dust collection or other tools.
While sitting around this fine dust builds up irritating molds, mildew and fungi that break it down into smaller even more dangerous airborne particles.


The third part of your question you did not ask is do we really need to move 800 to 1000 CFM for collecting the fine dust while 450 CFM does a great job collecting the heavier dust? The answer is yes and we all know why from using our shop vacuums. Sucked air only collects over a tiny area because airspeed drops off at pi times the cube of the distance. Getting the needed 50 FPM airspeed out far enough to capture the fine dust requires moving a lot more air than just gathering the chips forced by our tool hoods right into our collection pipes. My web pages share more information with the calculations and testing results.

Hope this helps.

bill

[David Less]

I refocused my design enhancements into building an overall more efficient cyclone and blower.
l

Bill,

Is this the same cyclone/blower type that can be purchased through Clear Vue using a 5 HP motor??

Thanks for the help and the wonderful research that you have done and provided.

David

[Michael Gabbay]

Bill - As usual your inforamtion is greatly appreciated. I have a Jet 1.5 DC with the AFF aftermarket bags. My duct work is 6" to 5" main run and either 5" or 4" at the machines (Oneida designed). It's in a small basement shop so the longest run is maybe 18'. I also run a AFS to clean the air. I know the AFS discussion has been somewhat controversial but my guess is it can't really hurt since it is picking up dust in the air.

The cyclone would be a better setup and will be on the short list of upgrades.

What does this type of setup present in terms of health hazards? Are you comparing dual bag DCs to cyclones based on the 30 micron stock bags?

I actually find the two worst offends for dust collection are the CMS and the table saw. My CMS dc needs to be redesigned to surround the saw better. With the TS I get more dust coming off the top of the table than I woul dliek to see. That can be corrected with an overarm guard.

Thanks, Mike

[Bill Pentz]

David,

Yes, Ed Morgano with Clear Vue Cyclones makes his plastic cyclones based upon my designs. Unlike other vendors who just plain lift my work, Ed is kind enough to pay me a small commission on sales to help with the fairly high overhead of my continuing dust collection testing, design, and web page work.

bill

[John Stevens]

Bill, thanks for the links. It's amazing what a difference it makes when you change the search terms on google. This area is of personal interest to me, because my wife has a pretty severe respiratory condition.

[Bill Pentz]

Michael,

Your 1.5 hp dust collector makes a great unit to hook with a short 6” diameter flex hose directly to your tools and then blow all outside, otherwise it quickly becomes challenged as a fine dust collector. The typical 4” of resistance from just a large hose, hood, and filters reduces the typical 1100 maximum CFM to a working bare 800 CFM for this size collector. Adding ducting and fine minimal resistance filters, or a smaller 4” hose or small 4” tool port pushes the overhead up enough that you lose the airflow needed for good fine dust collection.

Many hobbyists get “sucked” into using commercial ducting designs that look nice but work poorly. Unlike a commercial shop designed with a blower big enough to power all down drops open at once, most hobbyists only have the power for a small dust collection blower. These hobbyist blowers can only move enough air for a single run at a time. With air at typical dust collection pressures more like water that will hardly compress at all, any obstruction or short length of pipe acts just like our valves on our garden hoses and kill the flow. The Dwyer Instruments testing pages show that ten diameters of a smaller duct will kill the overall system airflow down to what that small pipe can support. For example my Jet DC-1100 dust collector that moves a real maximum 1100 CFM will only move 452 CFM through a short length of 4” pipe. The velocity is more than ample to keep the vertical down drop clear, but when that 452 CFM hits the main the airspeed is too low to keep the duct from building up dangerous dust piles.

I have long used a good air cleaner in my shop. It is worthless for protecting me as I work, but it does keep the volumes of fine dust from building up and helps keep my cars that get parked in the same area cleaner. Although I could do the same job with my cyclone and fine filters, the cost to run it the six plus hours needed would be prohibitive, plus unlike my aircleaner, the cyclone fails to properly stir the air, so keeps cleaning the same "racetrack" of air over and over.

ASHRAE recommends that we use a pre-filter or separator before our fine dust filters to keep them from plugging too quickly. They also recommend the filter area be at least 1 square foot of filter area for every 2 CFM of airflow. We use the cyclones to protect these fine cartridge filters from getting plugged too quickly and from material hits punching holes. My doctor and many other health professionals recommend those of us with respiratory concerns use 0.2-micron filters. Again, you still need to upgrade tool hoods, ports, ducting, and cyclone to make these filters do the job on fine dust collection.

I fully agree with you on our table saws and miter saws pumping out lots of dust. Both need collection at the blade guard and either under or behind the blade. I suggest on my web pages use of 6” down drop that goes to a 5” lower port and 3.5” upper hose for both types of saws. The worst dust producer in my shop is not any of my big iron, but instead my powerful hand held power sanders that swing from 5" to 10” sanding discs. They make so much fine dust, the only way to avoid a fine dust problem is to work outside with a mask on.

bill

[Allan Johanson]

Thanks again for all your efforts, Bill.

I've been testing some of the DCs for the local guys and every time I do, their eyes open wide when they can see for themselves the penalities of using too small ducting or poorly constructed duct runs.

Restrictive tools are another issue that I've been trying to make people aware of which leads to better hood design. You know something can be made better when I have a strong DC and have measured over 1400cfm in my 7" main duct.....then add on a 7x6 reducer, some flex hose and bolt it up to a custom made 6" port on a benchtop planer and the cfm will drop to 780cfm.

Over 600 cfm was lost! A chunk of that will be through the ducting, but even more was lost because of the hood design and the limited openings in the tools.

You get the same loss of airflow if you use the factory port on a Performax 16-32 sander.

I've exchanged several e-mails with Don Beale about hood designs and he has encouraged me to get more into this area. He wanted to do it but has no time and wants me to run with it. I'll do that when I get the house renovations done and I'll keep you posted.

Cheers,

Allan

[Jim O'Dell]

Bill, good to see you posting again here at the creek! I think I can safely say we are all very appreciative of the work you have done in this area. There will always be debates as to which unit is best, we all know that. But if the awareness you have raised about this problem helps some of us healthwise, then you have done a marvelous service to us and our families.
By the way, I now have my Clear Vue up, but still no power to the shop to get it running yet. As a side note, the motor on my unit is about 3 inches from the roof decking at the peak of a gabled end. Is there a "best" method of getting air on it to keep it cool? After some discussions here at the creek with several others, I have decided to put a powered roof vent close to the unit that will help expel heat from the attic, but am curious if there is a preferred method from your experience.
Thanks again for your valuable information. Jim.

[Bill Pentz]

Jim,

You probably will not need to do anything for extra cooling, but should keep an eye on the motor temperature. If it gets too hot, then wire up a little muffin fan to blow more air over the motor top.

*smile*

bill

[Dan Forman]

Bill---I suppose a number of us new buyers would be interested in your opinion of Oneida's 2 HP Gorilla cyclone. For those of us working in basement shops, there aren't a lot of options due to low ceilings. Your design was ruled out for lack of height. I must go back to your site to refresh my memory on ductwork recommendations. Is anyone making larger than stock dust ports for things such as table saws? For those of us who don't work with metal, tool modifications are a daunting task.

Dan

[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...:o... 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 (http://www.ablett.jp/workshop/cyclone.htm) <-- 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.


http://BillPentz.com/Woodworking/Cyclone/CycloneSideOutlet.gif

http://BillPentz.com/Woodworking/Cyclone/CycloneSideOutlet2.gif

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 (http://billpentz.com/woodworking/cyclone/CycloneMods.cfm) , 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:


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.

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.

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.

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:


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.

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.

The blower outlet should be the same size or bigger than the cyclone inlet to prevent an airflow killing constriction?

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.

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.


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:


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.

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.

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:


FPM varies CFM divided by duct area: FPM = CFM / Area measured in square feet.

CFM varies Directly with RPM: (CFM1 / CFM2 = RPM1 / RPM2)

SP varies with the SQUARE of the RPM: (SP1 / SP2) = (RPM1 / RPM2)^2

HP varies with the CUBE of the RPM: (HP1 / HP2 = (RPM1 / RPM2)^3

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 (http://www.cincinnatifan.com/pdfs/PB(R).pdf) 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.

[Stu Ablett in Tokyo Japan]

Turning the blower and mounting it off the cylone is what I did...........

http://www.ablett.jp/workshop/images/cyclone/filter_stack_mock_up.jpg
The blower is the big red thing to the right.

http://www.ablett.jp/workshop/images/cyclone/overall_view_with_blower_flex_hose.jpg

Not the best situation, but then again, neither is this for getting into and out of my shop.....

http://www.ablett.jp/workshop/images/dc/getting_close_to_lift_off.jpg

Cheers!

[Dan Forman]

Stu---What's it measure floor to highest point? I don't envy your shop entrance!

Dan

[Jim O'Dell]

Stu---snip I don't envy your shop entrance!

Dan

That's not an entrance, that's a trap door for potential burglers!!! Jim.

[Stu Ablett in Tokyo Japan]

I think it is right around 250 cm, so just a smidge over 98", but I did not go out the side of the cyclone like Mr. Pentz shows you can do, I just used two 45 elbows to make the corner.

Cheers!

[Boyd Gathwright]

Hello Bill,

.... Just wanted to say hi. It's good to be reading your “post” once again. Your “posts” are a very good reminder to me of how serious this problem is and can be. I treat it with the utmost respect, especially after reading some of the comments “posted” here. I have known people in my past who have been on and off of oxygen and in one particular case let me know he felt like a “dog tied to a tin can”. Of course, when you're young, you have your health and with time and the environment and bad habits you wake up one day without your good health especially when the safeguards are NOT in place.

.... Since you're now finding that we need to be down around .01 / .02 microns. I think I will take another look at my system.

.... Thanks again, it has been good hearing from you and the best of luck to you :).

Boyd



Emails this morning scolded me for not posting this as a new thread, plus leaving a few things off. Here is an updated version of what I shared at the end of the last cyclone thread. bill

Making a dust collection decision requires you to first decide on what it is you want to do. If you just want a shop with no chips, then just about any hobbyist 1.5 hp or larger dust collector or cyclone will work well for you because you only need about 450 CFM airflow for chip collection. If you seriously want to get the airborne fine dust in your shop under control then you have a whole different set of concerns. You can go to my web pages and study for yourself the dangers of fine dust and what it takes to control, collect and get rid of it.

(too long but Con't).

bill

[David Less]

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

Dan

Dan,

Sorry I didn't get back sooner. My ceiling height at the bottom of my rafters is 80". The height at the bottom of my ceiling (excluding rafters) is 87".
The cyclone unit will be 76" tall. I will run 9" diameter flex hose from the cyclone top to the blower top. This will produce about a 12" radius which will be between the rafters.

Hope this helps,

David

[David Less]

I forgot to mention that I will have to make a custom chip can. The height will only be 18" tall. I will have to empty often but it's a small price to pay for being able to use a good system. I would use caution, according the the master (Bill P.) short cyclones are not effecient for propper dust/air separation. I would rather change a chip can rather than deal with a dirty and constantly plugging filter canister. Not to mention the loss of CFM's.

David

[Bill Pentz]

Boyd,

Nice to be back, but my health remains less than stellar so don’t expect much. After most of a year in bed on oxygen, my employer required me to retire a year ago June. I've slowly recovered enough that I am now back on my feet a couple of hours a day and only on oxygen at night. I’ve been spending my up time fielding emails and slowly working on my web pages that seem to improving along with my knowledge. Again my goal is not to get wealthy, but to help others avoid landing in the same place.

Between my age, disposition, and health this thread and the Festool thread left me a little exhausted and frustrated. Instead of the normal few hours of emails, I easily had more than twenty hours worth of work since last Friday which is more than I can do, so woke up today pretty out of it.

bill

[Peter Gavin]

Bill,

I only have a 1.5 HP blower that is currently connected to a bag filter system. If I exhaust the air outside (without any bags), and use a 6" diameter solid run (about 6' long) to a central drop in my shop, and then use 6" flex hose (one machine connection only) to connect to my Machines (I guess I would need about 8' to reach all of them), how badly underpowered am I?

Thanks for all of your advise.

Peter Gavin

[Bill Pentz]

Peter,

Using the Static Calculator (http://billpentz.com/woodworking/cyclone/StaticCalc.xls) that Don Beale and I built you end up with 3.3" of static pressure for 1 6" hood and 14' of smooth walled flex hose with no filters. Depending upon your blower model (impeller size and blower housing size/configuration) you could have anything from 900 to a reall 1100 CFM maximum. That leaves you with a real airflow of between 690 and 793 CFM.

bill

[Allan Johanson]

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

You're very welcome, Bill. A long time ago I decided to try and help folks in a small way by trying to provide some "real" numbers instead of excessive theory, guessing or my ultimate favourite, "doing _____ will really hurt your performance". Really? How much will _____ affect things? I really wanted to know. So I set out to discover this for myself.

This Saturday I'll be at a friend's place where we installed a brand new Lee Valley aftermarket filter bag on his 2HP DC a while back. Now that he has a typical dust cake on it, I'll bring out the same piece of pipe I used many months ago and measure the airflow.

With the old factory bag after a good shaking it flowed 700cfm.
With the brand new LV bag it flowed 930 cfm.
What will it flow now???

Some folks think that giving a typical filter bag a quick shake will restore 100% of the airflow. My spider sense is telling me otherwise, but I do wish that were true. We'll see what the testing gear says. I'm looking forward to it.

Take care of yourself, Bill.

Allan

[Allan Johanson]

Peter and Bill,

Here's some test info that might help:

With my friend's 2HP DC I just mentioned in the other post, we also wanted to know what was the impact of the bags - period. So we ran a couple tests without the bags hooked up. We disconnected the blower outlet hose at the blower, so it still had the rectangular to 5" round adapter on the blower, just no flex hose on it. It just blew the air straight up towards the ceiling.

2HP DC with a 12" fan and factory 5" blower inlet/outlet

- short length of 5" solid pipe with factory bag....630 cfm
- short length of 5" solid pipe with new LV bag....810 cfm
- short length of 5" solid pipe with no bag..........900 cfm

Replace factory 5" blower inlet cover with a homemade 6" version so we could hook up a 6" test pipe:

- short length of 6" solid pipe with factory bag....700 cfm
- short length of 6" solid pipe with new LV bag....930 cfm
- short length of 6" solid pipe with no bag.......>1100 cfm

BTW, the more restrictive the ducting and tool, the less benefit you'll get to removing the bags. When we choked the 5" test pipe with a 5x4 reducer, the airflow went like this:

- 5" test pipe with 5x4 reducer and old factory bag....550 cfm
- 5" test pipe with 5x4 reducer and no bag...............700 cfm

********

If you want to really reduce the restriction of the exhaust pipe to outside, you should make it as large as possible. Replace the typical rectangular to 5" round blower exhaust adapter with something much, much larger. 8" solid pipe can be purchased at the BORG. Try that (or larger!) for max benefit.

If you can wait a bit maybe I can run another test for you (if I remember :D ). I can see about taking a measurement with no bags attached and with a 5' long 5" diameter solid pipe hooked up to the blower exhaust. I'm way too curious for my own good. :eek:

Good luck!

Allan

[Jim O'Dell]

Bill, when we get to be too much for you, tell us!!! Take some time out. We don't want to wear you out or take all your "feeling good" time, I'm sure you have other interests. We'll be here when you can get back to us!! Jim.

[Bart Leetch]

[

If you can wait a bit maybe I can run another test for you (if I remember :D ). I can see about taking a measurement with no bags attached and with a 5' long 5" diameter solid pipe hooked up to the blower exhaust. I'm way too curious for my own good. :eek:

Good luck!

Allan[/QUOTE]


Did you check what the max amps the motor is allowed to pull & then check what amps your are pulling with each one of these changes?

[Allan Johanson]

Did you check what the max amps the motor is allowed to pull & then check what amps your are pulling with each one of these changes?

Hi Bart,

I didn't bother checking the amp draw at that time. This particular DC (Trademaster - a Canadian "generic import" brand) has a massive motor rated for 12 amps @ 230V. When we did the "no bag" airflow test the DC only ran for a few seconds before we shut it off.

Most 2HP DCs have an 8-9amp motor so your concern is indeed valid and one that anyone messing with their DCs might want to think about.

My old 2HP DC (Samona - another generic Canadian brand) had a 9amp motor and 5" inlet/outlet. With the factory bag and some 5" flex hose it drew 7amps. With the added resistance of a duct network you'd be able to do a few mods to help compensate for the ducting before potentially running into trouble. But on that DC, running a 6" inlet with no bags might shorten the lifespan of the motor due to excessive current draw. I wish I still had that DC for testing purposes.

Cheers,

Allan