Dust Collection Research - Blower

Dust Collection Research - Blower

You need to know a few things before you chase down your parts.

HAIYANG supply professional and honest service.

1. Motors

   Barry owns Electric Motor Warehouse and he has decades of motor experience. He volunteered his time to help me learn more about electric motors to help me select the best motor to power my cyclone. I told Barry I like Baldor motors because my earlier projects used Baldor motors extensively. Barry warned me that Baldor imports most under 10 horsepower motors now. He said these imported Baldor motors provide poor quality and they fail often. Now he recommends the American made Leeson motors.
   
   Barry asked me to define my needs. I explained I needed a motor to power my cyclone blower. Because blower technology is mature most blowers of the same type and motor speed have near identical performance. This means we can size our blower and motor using any good fan table. A fan table will tell us the required impeller size, motor size, and ducting size if we know the static pressure and required airflow. We have the cubic feet per minute requirement tables from vendors who guarantee their customers a particular air quality. These tables show we need at least 1000 cubic feet per minute airflow at our larger stationary tools to get good fine dust collection. Also, my Static Pressure Calculator shows a typical two car garage sized shop generates 4" to 10" static pressure resistance meaning the friction and overhead from our ducting, fittings, hoods, and filters. We also know we want to use a backward curved (BC) type impeller to minimize noise. The Cincinnati Fan pressure blower table shows we need at least a 14" diameter BC impeller turning at 3450 RPM. At the minimum 4" resistance level this 14" impeller uses 3.27 horsepower to move a maximum 1377 CFM airflow. At the maximum 10" resistance level this 14" impeller only uses 2.34 horsepower but it then only moves only 846 CFM. Clearly the 1000 CFM minimum requires at least a 15" impeller, but 15" impellers proved near impossible to find, so early on I decided to just use a 14" diameter BC impeller and settle for less fine dust collection. I now have a few impellers custom made with the compression arbors, or you can buy a commercial blower and impeller. The 15" diameter works well, or you can upgrade to a 16" for even more airflow and better use the capacity of a full 5 hp motor.
   
   Barry explained that dust collection motors tend to be the heaviest we use in our shops so he recommends buying the best quality possible. Unlike a fan, dust collection equipment uses very large heavy impellers with lots of air resistance that cause very high starting loads. Any except heavy duty motors built to handle these high startup loads will burn up. Even these heavy duty motors come with a caution to not start them more than about 6 times an hour. The startup load is so high that it takes at least ten minutes of running to get rid of the extra heat. If started too often that heat builds too fast and the motor will burn up. Most compressor, pump, and farm duty motors will handle these high startup loads and up to the six starts an hour. He said the normal single phase heavy duty motors come in 1, 2, 3 and 5 horsepower models. Most with larger needs use 5, 7.5, 10 and 15 horsepower three phase motors. Three phase requires three-phase power or a phase converter, but these motors don't need the special starting circuits that often fail on smaller single phase motors. Additionally, all quality motors come with different service factors. A 1.0 service factor motor can run at 100% of its rated amperage without overheating. A motor with a 0.5 service factor should never be run more than half time or it will overheat and can burn up. These low service factor motors are often used for fixed purposes such as opening a gate and have heat sensors that limit how much they can run. Alternatively, a 1.10 service factor motor can run at 110% of its maximum rated horsepower without overheating as long as it is not used in an already hot environment. The warmest place in a shop is at our ceilings or between rafters. Why buy a 1.10 service factor 3 hp motor when I knew that with the typical 14" diameter backward curved impeller that almost all cyclone makers use we would regularly pull 3.47 hp? Add that to mounting this motor in the hottest place in our shops and 3 hp motors will eventually burn up. Buying a 3 hp motor made no sense when it cost only $20 more to buy a real 5 hp motor that could handle the load, heat, and startups. Since motors need the same power to turn the same sized impeller, the operating costs are near identical without having to worry about replacing motors from being overheated too often. I opted for the 5 hp Leeson motor which not only lets our motors stay cool by running well below its rated horsepower, but also lets us configure with a larger blower impeller to use some of that extra horsepower. Although most do not need the larger 15" or 16" impellers if they use the all 7" diameter ducting and port sizes I recommend, you really should use a 15" or 16" diameter impeller if you use 6" duct. Otherwise, there is not enough pressure to move enough air through your duct. I found using a 16" diameter impeller makes a big difference in my shop, as I have a number of tools that just could not be modified to accept bigger ports. This larger impeller allows use of all 6" diameter ducting and so increases the pressure that it pulls enough air through my pairs of smaller 4" ports on machines with two ports. It will not move enough air with a single 4" port. Regardless, these Leeson motors are real 5 hp motors, not the inflated hp motors used on some vacuums and inexpensive air compressors.
   
   Barry also explained that when we make a blower, we need to use a face frame motor mount instead of a normal base mounted motor. The two pictured motors show the difference between a face frame mount and normal mount. The one on the left is a face frame mount meaning the front of the motor, that aluminum area, bolts directly to the blower housing. Note how the air holes wrap around to the side of that face so the needed cooling air can blow off to the side. The motor on the right is a standard mount and it has its cooling holes in front next to the motor shaft. These holes would be blocked if you mounted its face right to the blower housing as we need to do to keep the heavy impeller as close to the motor bearings as possible. Barry was willing to setup these motors with a face frame mount for no additional charge. I said go for it.
   
   That 5 hp Leeson heavy duty real 5 hp motor has been my motor of choice ever since. Barry not only provided these motors to small shop woodworkers with the face frame mounts, he also provides them at a considerable discount and waived all commission to make that pricing even lower. They offer the Leeson Model # P145K34DB1B, 3450 rpm, 5 hp, 7/8" shaft, 20.8 rated amp motor with the added face frame mount: Leeson Motor Part #120554.00 part #175181. Electric Motor Warehouse as a favor to hobbyists prices this below what other dealers must pay in quantity 100. If you order this one, be sure to ask for having the face frame mounted for you and setup for CCW rotation. The next best and most affordable alternative is to buy a refurbished 3450 RPM pump motor locally. Most motors require careful installation to ensure ample airflow to keep from overheating. Click the following link to see the custom Electric Motor Warehouse 5 hp motor setup up for fellow woodworkers! http://rover.ebay.com/rover/1/711-53200-19255-0/1?icep_ff3=2&pub=5575168271&toolid=10001&campid=5337860386&customid=Electric+Motor&icep_item=400342556275&ipn=psmain&icep_vectorid=229466&kwid=902099&mtid=824&kw=lg).
   
   If my pocketbook said otherwise, I once could have made do by going to my local Harbor Freight (HF) store with my discount coupon and grab on sale their 5 hp compressor motor. These used to be only 3 hp motors, but HF had so many returned they for a short time sold real 5 hp compressor duty motors. They had shaft sizes that were too small, so required a special arbor for our impellers which made the costs nearly as high as just getting a good Leeson motor. Unfortunately, Harbor Freight quit selling these, so you are going to have to look elsewhere.

2. Impeller Material

   I strongly recommend use of steel backward curved material handling impellers. Material handling impellers are made of heavy steel, are self cleaning, and handle the hits and impacts of a normal dust collector that passes all through the impeller. Unfortunately a full dustbin, a plug in the cyclone cone, clumps of debris, a large surge of dust, or an air leak turns our cyclones into little more than a pipe that passes all right through the blower. This heavier junk we can suck up can severely damage any lightweight impeller and even cause them to explode. It can also rapidly build up on non self cleaning impellers, create a bad out of balance condition, and cause our motor bearings to fail. Between the potential for material hits, need to move a high volume of air, need for self-cleaning, and need to provide higher pressure, most available fans, aluminum impellers, plastic impellers, squirrel cage impellers, vacuum impellers, and airfoil impellers will not work to safely power a dust collector or cyclone.
   
   I wish I could drop it right here, but our small shop dust collection market continues to be bombarded with just plain bad information and equipment that ends up with my either having to answer innumerable email questions or respond on these pages. The same magazine top rated vendor who sold cyclones with plastic impellers and still produces expensive cyclones that provide little better separation than trashcan separator lids has overwhelmed small shop woodworkers with their advertizing the benefits of their aluminum alloy impellers. So many believe that nonsense that my choices are to either respond here or have to deal with far too many emails addressing the serious issues with aluminum impellers that leave me only recommending heavy steel impellers. This vendor correctly shares that because of their light weight aluminum alloy impellers come up to speed faster with a smaller starting load on our blower motors. What this vendor fails to share are the many important reasons why we should not use aluminum alloy impellers to power either a dust collector or cyclone.

   1. Although aluminum alloy impellers are cheaper to make, the major commercial blower makers strongly recommend against use of aluminum alloy impellers for dust collection. Their main concern is when the inevitable heavy block, knot, tool, nail, screw or other item gets sucked up and goes through the impeller these aluminum alloy impellers can explode.
      
      A number of small shop woodworkers complained on the major Internet based dust collection forums because their expensive cyclone blower aluminum alloy impellers exploded when hit with wood knots and other stuff sucked up by their cyclones. Sadly, all of those kinds of posts rapidly vanished from the major Internet woodworking forums whose livelihood depends upon vendor advertizing.

   2. This same cyclone vendor strongly puts down steel impellers on their web pages implying that steel impellers are so heavy they ruin motors from the high starting loads. This vendor uses undersized motors with high service factors meaning they can run at 125% of maximum power. This in the most open air configuration which is what they use for advertising, lets them claim far over 1000 CFM airflows. In real use with ducting, tool hoods, and filters, these units don't move nearly as much air. In fact you will be lucky to get 785 CFM when pulling through a 6" duct and barely 349 CFM when pulling through a 4" duct. As discussed before if you choose to use the gravely undersized motors this vendor sells, this startup load is a serious problem because it can quickly cause a motor to burn out from overheating. With a properly sized motor to handle the startup loads this concern is irrelevant.

   3. This same vendor also states on their web pages that steel impellers are a major fire risk and do not comply with the National Fire Protection Association (NFPA) guidelines. That is double nonsense.
      
      This same NFPA guideline also requires either putting our cyclones and blowers outside behind a suitable explosion barrier or using certified fire and explosion proof cyclone equipment. This vendor makes an indoor cyclone that is not certified as either fire or explosion proof. They would never pass that certification process because they use steel instead of aluminum blower housing and a plastic hose connected to a cardboard dust bin.
      
      Worse, if you look up the current warnings you will find that the experts on ventilation recommend against use of aluminum impellers. From the ACGIH's Industrial Ventilation: A Manual of Recommended Practice for Design, page 7-22, 26th Edition, 2007:
      
      "For many years aluminum alloy impellers have been specified to minimize sparking if the impeller were to contact other steel parts. This is still accepted, but tests by the U.S. Bureau of Mines and others have demonstrated that impact of aluminum with rusty steel creates a Thermite reaction and thus possible ignition hazards. Special care must be taken when aluminum alloys are used in the presence of steel."
      
      For those who don't recognize what a thermite reaction is, you already know because Fourth of July sparklers are made from powdered aluminum that when lit burn with a very bright, hot, high intensity flame. In other words, if you sucked up a rusty nail it could knock off a small piece of aluminum creating the equivalent of throwing part of a lit sparkler into either your dust bin or filter. Since I first wrote this page NFPA has acknowledged this thermite generated fire problem and now no longer recommends the use of aluminum and aluminum alloy impellers. So much for one vendor's touting their non-sparking impellers.

   4. Another frequent complaint with the aluminum impellers which also gets quickly deleted if shared on the Internet forums is the problem with these light aluminum alloy impellers slipping down the motor shafts then self destructing when they hit the blower housing. The major commercial blower makers use special star tipped set screws and a keyway to secure their aluminum impellers. They also warn that these impellers are not to be used on a vertical motor shaft because set screws cannot carry the weight of the impeller. When these impellers are mounted on a horizontal shaft the shaft carries the weight and there is almost no side to side pressure. When mounted on a vertical shaft the commercial blower makers strongly recommend using a tapered shafted motor with a bolt which screws into the motor shaft to lock in the impeller or use a compression arbor similar to what we use in our routers to hold bits securely when mounting impellers on a vertical shaft.

   In short, I strongly recommend against buying any cyclone with an aluminum alloy impeller and instead buying a good well balanced steel impeller.

3. Impeller Sizing

   This is one of those areas where I provide far more information than many want or need to know, so the bottom line is if you use the Leeson 5 hp motor I recommend you use a 16" diameter impeller to get the maximum airflow and pressure from your motor. This added airflow and pressure are important. The increased airflow does a much better job collecting the fine dust and the increased pressure permits you to use all 6" diameter ducting and still move over 1200 CFM to any tool in your shop. How I got to this recommendation is a touch complicated.
   
   My engineering professor friends who helped me test every major brand and size of small shop dust collector and cyclone a few years ago were appalled at how poorly our small shop blowers were made. We actually had one small shop vendor who supplied exactly the same sized impeller with their 1.5 hp, 2 hp, and 3 hp dust collectors and cyclones. With our motors all turning at the same 3450 RPM for U.S. 60 cycle current, every one of those blowers moved exactly the same amount of air. What was very disappointing was finding only the Delta, Jet and Powermatic impellers were actually properly sized for their blowers. All others were either way too small or too large. An undersized impeller just spins leaving a good portion of your motor's horsepower unused. An over sized impeller is required if you have a high resistance, but if it is tested without that resistance you get the incredibly high CFM numbers that so many of the less reputable vendors advertise. Worse, at these high CFM numbers from running in "free air" meaning with no resistance our motors are doing the most work. In our testing we found a number of cyclones 3 hp and smaller that frankly were running such over sized impellers which cased the motors to run so far above the motor horsepower we had two motors burn up. Talking with the testing groups that ran some recent woodworker magazine cyclone tests they had the same problem and burned up three cyclone motors when testing. Vendors simply used way over sized impellers and then choked them down in real use with undersized ducting to save their motors. Unfortunately, they had to so choke down their impellers that not one in real use working against typical shop higher resistance levels with real ducting sized as they recommend moved a real 800 CFM let alone the 1000 CFM we need for good fine dust collection.
   
   Because blower technology is mature, blowers of the same type and size provide near identical performance regardless of which commercial vendor we use. This means we can look at any good commercial fan table and use that table to size our impeller, our ducting main and our motor horsepower requirements. To use one of these fan tables we need to know three things, required minimum air volume, maximum resistance and minimum resistance.
   
   Air engineers long ago learned we must capture the fine airborne dust as it is made. A few of the newer tools such as the circular powered hand saw from Festool have proven that if tools are built from the ground up to totally contain all of the dust being made we can get excellent fine dust collection with a large shop vacuum. Unfortunately, almost all stationary tools come with little to no fine dust collection built in. As a result these tools make so much fine dust that spreads so rapidly normal exhaust fans and air cleaners cannot pull the airborne dust level down fast enough to ensure passing an air quality test. As a result, we have to collect the fine dust as it is made.
   
   Because almost every customer wants good fine dust collection without having to replace all their tools, air engineers long ago worked out how to ensure our typical stationary tool designs got good fine dust collection. To collect the fine dust at each source they found we have to start by making sure each tool is equipped with hoods that block all fast moving air streams. Additionally, we also must surround the working area of each tool with a "bubble" of air moving at least 50 FPM to overcome normal room air currents. The size of this bubble is defined by what level of fine dust collection we want. Air engineers did years of testing to determine how big of a "bubble" it takes to pull in the fine dust. Once we know the size of that "bubble" we can use the sphere surface area formula to compute the area of that sphere where A=4*Pi*r*r then put in our 50 FPM airspeed and that area with a little algebra into our air formula FPM=CFM/Area to calculate our needed CFM air volumes. A couple of decades of testing and experience have verified we need at our larger stationary tools that have upgraded hoods about 800 CFM to create a minimum "bubble" ample to meet OSHA air quality standards, roughly 900 CFM to meet ACGIH recommended air quality, and about 1000 CFM to meet medical and EPA recommendations.
   
   Sadly most small shop woodworkers and even most vendors wrongly assume that the roughly 350 CFM that provides excellent "chip collection" at our larger tools will also provide plenty of airflow to pull in the fine dust we know we can move with the lightest breath. The problem with this assumption is we are thinking in terms of blown instead of sucked air. Blowing a directed stream of air will hold together for quite a distance, but sucking has the airspeed fall off at roughly twelve times the distance squared because the air comes from all directions at once. You can easily test this. Wet a finger and see how far you can move it from your lips and still feel blown air. Try it again while sucking. Almost all can feel the blown air as far as they can reach. Conversely, we can only feel the sucked air out to a couple of inches. To cover a large area with sucked air we have to move a large volume.
   
   We can pick which air quality level we want and then use that required CFM value with our fan tables to pick our impeller size. Although many recommend the OSHA air quality levels that we can get with 800 CFM, I strongly recommend using medical and EPA recommended air quality levels that instead require at least 1000 CFM airflow to our larger tools.
   
   Before we can use our fan table we also need to know the highest and lowest resistance levels in our shop. The resistance is a measure of how much work our blower has to do to overcome the friction in our ducts, to turn the corners through wyes and elbows, to pull through a restrictive hood, and to push through a dirty filter. We measure this resistance in what are known as water column inches, meaning how high a blower would have to push or pull a column of water to overcome that resistance. We can add up the various resistance numbers by hand or do testing once we get our shop ducting built, but the most convenient way to calculate shop resistance is to use an already setup spreadsheet that lets us put in what we have then calculates the overall resistance levels. A good static calculator such as the one shared on these pages shows that a typical two car garage sized shop will have a minimum resistance of about 4" when connecting to an adjacent tool with a new clean filter.
   
   Calculating the maximum resistance is a little more difficult. We have to calculate our highest resistance ducting run then add the resistance of our filter, which changes over time. We normally calculate the worst case ducting situation in our shops to allow us to later move any tool to any location. Otherwise we would be forced to wheel our dust collector or cyclone right next to each tool. The maximum ducting resistance is for a distant tool that has two collection points like a table saw with both cabinet and over blade collection for a typical two-car garage sized shop ends up being right at 7 water column inches in most shops that use a 6" main and downdrops. A 7" main often drops this to only 5 water column inches. Next, we have to add the resistance of our filter which changes over time.
   
   As our filters age, they build up dust trapped in the filter pores that does not come out with normal cleaning. This is called seasoning. The stuff trapped in the filter pores improves filtering by up to twenty fold in a fully seasoned filter, but also increases our resistance significantly. It typically takes nine to twelve deep cleaning cycles meaning as much as a couple of years before small shop woodworkers fully season our filters. Our having to breathe the finest invisible dust known to cause serious health problems for a few years while waiting for our filters to fully season is why I strongly dislike most small shop vendors advertizing "seasoned" filtering levels. The American Society of Heating, Refrigeration, and Air-conditioning Engineers (ASHRAE) is considered the world authority on filter measurement and performance. Our small shop vendors almost universally ignore the ASHRAE standard that requires all indoor filters, meaning those used in our shops, must be rated when clean and new. Our small shop vendors instead rate their filters after becoming "fully seasoned". Anyhow, in terms of resistance most small shop fine filters start out brand new with only about 0.5" of resistance then as they season their resistance will climb to 2.5" to 3" just after cleaning.
   
   While in use our filters also build up a layer or cake of dust on the filter surfaces and this cake rapidly kills airflow. The smaller the filter area the faster the dust builds, the more the airflow gets killed, and more often we must clean our filters. Unfortunately, the more often we clean our filters the shorter they last. Most larger woodworking facilities use pressure sensors that set off a cleaning buzzer when the filter resistance gets more than 2 to 2.5 water column inches higher than the seasoned filter resistance. Letting the dust build any higher kills the airflow needed for good collection.
   
   Additionally, they also use these meters to show when it is time to change out their filters. As our filters age, they wear out meaning the pores get larger and larger until they no longer trap the finer particles. As the pores get larger the filter resistance drops as the air goes through with less resistance. As soon as the after cleaning pressure drops more than 1 water column inch below the maximum seasoned rating, the filter has become so open it must be changed out. Most commercial shops must change out their fine filters roughly every three months of full time woodworking.
   
   So, to calculate maximum pressure we add the 7 water column inches for our maximum ducting resistance then add 2.5 inches more for our seasoned filter, plus 2.5 inches more for a maximum resistance of about 12 water column inches in most typical two-car garage sized shops and about 14 water column inches for most three-car garage sized larger shops.
   
   This 4" to 12" average pressure range coupled with the 800 to 1000 CFM is what requires us to use pressure blowers for dust collection. The other types of blowers either move too little air like vacuums or like most squirrel cage fans and airfoil impellers just cannot generate enough pressure to overcome our normal ducting, tool, and filter resistance. We also know we need heavy duty steel material handling impellers to ensure we do not break our impellers with inevitable material hits. We also need these material handling impellers to keep strings and shaving from getting caught on our impellers that would cause them to go out of balance and quickly ruin motor bearings. For our indoor dust collector and cyclones where noise is a serious consideration, we also want a backward curved (BC) impeller blade to minimize noise problems.
   
   Finally knowing our airflow and pressures we can look up our needed information from a good fan table. Because material handling blowers are a very mature technology, looking at almost any major commercial blower maker gives near identical results. So if we go to the steel pressure blower fan table shared by Cincinnati Fan we see by looking down the 12" pressure column the first blower that will move at least our needed 1000 CFM is SPB15 blower housing with a 15.5" diameter impeller that has 3.5" tall blades. The blower table shows this impeller will move a real 1022 CFM at 12" and draws a real 3.44 hp. That table also shows it will move this much air through a 6" blower opening which matches our main duct. If we look a few entries lower in the table we see this same impeller and blower with a 8" opening and 8" main will move 1108 CFM and draw 3.61 hp. This sizes our ideal impeller at 15.5" based on that blower table. It also sizes our main at 6", 7" or 8" and it also sizes our minimum down drop size to 6". Anything smaller for a down drop will reduce the flow enough that there is not enough airspeed to keep the mains from plugging or building up ducting dust piles that pose a serious fire risk. To size our blower motor we simply look at this same impeller at our minimum resistance level. This 15.5" diameter impeller at 4" of resistance moves a real 1957 CFM and draws a real 4.88 hp which is why I have long recommended use of a 5 hp blower motor with at least a 15" diameter impeller and at least 6" diameter ducting.
   
   Almost all small shop vendors error by supplying their larger cyclones with only 14" diameter impellers and only 2 or 3 hp motors. We can use the same blower table and see that a 14" diameter impeller is so challenged by resistance that it does not even perform once over 11" of resistance. At 9" of average resistance it only moves 767 CFM and draws 2.05 hp. This tells us clearly we don't ever want a 2 hp motor because during normal average every day dust collection it is working at over 100%. That 767 CFM provides good chip collection that only requires 350 CFM but is far short of the 1000 CFM needed for good fine dust collection. Next, look at what kind of airflow we get at the expected 12" of resistance with the typical two-car garage size shop longest ducting run. At 12" resistance this 14" impeller moves so little air with such an unsteady flow that it does not even have a value in this table and will not even move enough air to provide the needed 350 CFM needed for good "chip collection". Next look at that same table and see what happens to the horsepower demand when the resistance is at a minimum meaning only 4" with that 14" diameter impeller. At 4" of resistance that impeller moves 1543 CFM while pulling 3.09 hp. Now look at that same table at what happens during the vendor supplied tests that instead use the 8" opening and main that the more popular cyclones use and recommend. At 4" static pressure the airflow climbs to 1893 CFM while the horsepower climbs to 3.68 hp which is well over 3 hp motor ratings even with large 1.1 (110%) service factors. Because the normal fixed speed 3450 RPM induction motors we use to power our dust collectors are made to pull starting loads six or more times their running loads, our vendors can get by with quick tests at these kinds of horsepower loads. Unfortunately, if these loads go on for a few minutes the motors will quickly overheat and burn up. The bottom line here is I have a really difficult time as an engineer wanting anything less than a 15" diameter impeller and good solid 5 hp motor for the heaviest used motor in my shop.
   
   I know that most don't want to spend more than needed. When I first put up this web page in 2000 the only affordable sources for impellers were the 14" diameter impellers we could buy as replacement parts for the larger 3 hp dust collectors. My 18" standard cyclone plans work with these 14" sized impellers, but are best with the 15" and 16" impellers I designed. Since we now have good sources for larger impellers I strongly recommend using one of them to get the larger airflows required for better fine dust collection.

4. Impeller Sourcing

   A few have made their own impellers but you need to know that the forces involved with a 14", 15" or 16" impeller turning at 3450 RPM are measured in the tons. I have already had one welded impeller I was testing fly apart from those turning forces. I have not hit the ground so quickly since in the Vietnam War. There was little left of my blower and I was amazed that the heavy PETG plastic used in Clear Vue Cyclones actually held up far better than the 18-gauge steel. The plastic was only scratched while the steel was punched clean clear through and badly ripped. Unless you really know what you are doing, making your own impeller or grabbing just any old impeller can be potentially life threatening. I see no reason to take this risk trying to save a few dollars while making my dust collection system, so strongly recommend use of a good quality impeller designed for this type of use.
   
   With no other affordable sources available I used to recommend ordering the Jet DC-1900 14" diameter impeller part number 431006 from Jet Customer Service at 800-274-6848. My cost in 2001 was $57.76 plus $15.00 more for shipping. Costs now are about double that after a huge increase in the price of steel and much higher shipping costs. To attach this impeller to your motor shaft you need a custom arbor. With too many unable to build their own arbors, I had a machine shop make up arbors and sold them at cost. These arbors worked but even with their special star tipped set screws that dig into the motor shaft they could let the impellers slide plus these screws need replaced every time you remove the impeller. Otherwise the impeller can slip on the shaft, so I shifted to a good compression arbor. My machinist bought the compression arbors then welded a round plate with holes to match the Jet impeller. My machinist retired after being there for me for over thirty years, so the supply of these arbors stopped. One of my local friends Roy does a little machining and made his own Jet impeller arbor. He is a very busy fellow and making arbors is not his priority, but he also likes to help others out. You can contact him at RMcbra@aol.com to see if he can make one for you, but you need to work out your arrangements with him.

   After a few years of a steady supply, Jet ran out of impellers and those of us wanting to build our own cyclones and blowers were left waiting for months. After looking all over others found Cincinnati Fans sells a very heavy aluminum material handling impeller and a lighter air movement impeller. Both came with warnings not to use them for dust collection because material hits could cause the impellers to explode. Many ignored my advice and used the less expensive lighter Cincinnati Fan cast aluminum alloy impellers. When challenged with all going right through the blower which happens with a plugged cyclone, full dust bin, bad air leak, or big surge of dust, these impellers were damaged with a few even exploded. Even their heavier cast aluminum alloy material handling impeller should not ever be exposed to impacts, which means this impeller should be used after the cyclone and filter cartridges. Regardless, I worked out with their corporate headquarters an arrangement to let small shop woodworkers buy these heavier impellers from their local dealers for reduced costs. Because of the way their dealer arrangements work, most dealers still charged almost double plus shipping. And yes, I know two other import firms sell impellers for less, but their quality just did not pass my inspection and with over twenty tons of force involved with a spinning impeller going with low quality or a poorly balanced impeller just makes no sense. The main advantage of these impellers is the light aluminum alloy construction permits the impeller to come up to speed quicker with less wear and tear on the motor. The biggest disadvantage of the aluminum alloy impellers is the NAFTA no longer allows them in new systems for commercial use because when hit with metal aluminum impellers launch white hot sparks that can cause fires.
   
   These impellers cannot be used directly as delivered because they need a different way to mount to the motor shafts (see impeller mounting below). These impellers are designed for mounting on horizontal motor shafts. They use special Allen set screws with star points that dig into the motor shaft to hold the impeller from moving sideways. These screws must be replaced every time they are loosened. With our cyclones we mount our motor shafts vertically. These screws do a poor job and were never meant to support the whole weight of the impeller. Cincinnati Fan, one of the top impeller makers warns to not use impellers mounted with set screws on vertical shafts as these impellers can and will slip with catastrophic results! Many including me learned the hard way that set screw mounted impellers slip down the motor shaft and destroy the blower housings. In one of my test runs, I failed to replace those special star set screws as recommended and my impeller slipped down the shaft doing bad things to the impeller, motor, and blower housing. This is why I made my housings with deeply recessed screws so the impeller blades hit wood instead of metal first, hopefully giving time to turn all off before a disaster. Anyhow, I quit recommending these aluminum alloy impellers after too many had problems.
   
   When Jet ran out of stock I paid to have a custom 14" material handling impeller built and certified by Sheldon's Engineering with a far better compression arbor. After three years of sales I was about one third paid back when the engineer I worked with left Sheldon's and that firm was sold. The new owners stopped honoring our agreement and stopped carefully packing the impellers they shipped so most arrived damaged and people complained to me. This never was intended to be a money making proposition, but I was not happy at covering that considerable loss and then having to do it all over again with another firm. Foolish or dedicated, I did so anyway for two more firms. I again subsidized the costs for test gear, testing, blower housing, and provided the engineering specifications. The first firm sent me an impeller that exploded due to poor workmanship in their welding and refused to make repair, so I moved on.
   
   I now have a machine shop make impellers for us and also have another firm CNC cut MDF top and bottom pieces to easily make a blower to work with that impeller. Electric Motor Warehouse provides discounted motors with the right face frame mounting. In a cyclone this 5 hp motor actually was left with over 1 hp of unused capacity, so I engineered a 16" impeller. It uses that extra horsepower, but does require a few changes to the cyclone design to get full use of that extra flow. As shared above if you step up to a bigger impeller, you also need to use different dimensions for your blower opening and motor plate from those shared below. Remember that these firms I have helping do small shop owners a favor. Please don't chase them away from helping us by burying them with questions and special orders.
   
   After considerable experience and lots of testing with the 15" impellers I decided there was enough unused capacity in our 5 hp motors to turn a larger impeller. My testing showed standard 16" impellers exceeded the capacity of our standard 5 hp motors, so I engineered a special 16" diameter impeller with slightly lower blades that provided additional pressure to move more air without putting our motors at risk. This is the impeller that is now used in the Clear Vue Max cyclones. I recommend using this impeller with a left handed version of my cyclone design for both optimum airflow and separation efficiency.
   
   Alternative Impeller When Clear Vue closed for a short while my son went back into making cyclone kits. Over the years I had improved my impeller designs and had four really good options both left and right hand rotating 15" impellers and 16" impellers. My son would only make one cyclone design, a single left handed 18" diameter cyclone optimized for both airflow and separation. Our blower template made blower housings for 15" diameter impellers. It was too small for the 16" impellers, so I engineered a special 15.5" impeller that my machinist, Inchs Machinery in Loomis, CA (916) 652-0628 built and sold directly. These have the advantage of fitting in the existing 15" blower housings with only tiny modifications to the hole that lets the blower housing slip over the mounted motor and impeller. Anyhow, these move the same air as the 16" diameter impellers which is as much air as you can move without putting your 5 hp motor at risk. They are really great well built impellers made of heavy steel built like tanks and use the best compression arbors. They are ideal to upgrade your existing 15" impeller or to use in place of the 16" impellers. I was talking with my machinist about my new cyclone project and he is still makes a few of the 15.5" impellers that he balances and powder coats. You will need to talk to them about pricing, availability and delivery.

5. Blower Housing

   I was stunned when my professor friends and I tested every major brand and size of small shop dust collector and cyclone a few years ago. Most of the impellers and especially the blower housings were incredibly poorly designed and even more poorly made. A blower impeller needs a shape that minimizes turbulence, but most small shop blowers had lots of rough edges, protruding rivets, etc. that cause lots of internal turbulence and disrupts flow. A blower housing requires a smooth spiral shape to provide a good steady airflow without causing pulsing which kills blower efficiency and raises sound levels dramatically. Most small shop dust collector and cyclone blowers, in fact all the major brands except for Delta, Jet and Powermatic had blowers with very poorly made housings. Many did not even use spiral shaped housings but instead round housings with the impeller offset to one side. Most blower housings forced round into square ducting and had very rough ridges, loose metal, and other junk pushed right into the air stream. The engineering professors I did this testing with were amazed. They said blower technology is mature and just about any engineering graduate can look up what it takes to make a far better material handling blower. What we found with our testing is only those three vendors had performance that matched industry norms and all others were below, some very badly. The worst was that highly rated aluminum impeller cyclone that used a circle shaped blower with an impeller that had the support castings for the blades in the middle of the airflow.

HVAC Fan: Should You Keep It Running on Auto or On?