Dust Collector Performance and measurement

[Chris Parks]

Why don't we measure the end result of our DE's at the exhaust? If a change is made and the flow/speed drops it was not good idea and vice versa.

[Ole Anderson]

Tough to do if you have a filter, which if removed, will affect performance. However, the same could be done by measuring the net pressure change with a manometer and using the fan performance curve. Reading the amp draw of the motor can also be a good indicator of performance change. Now if the manufacturers would only give us the amp draw curve on the fan performance curve.

[Chris Parks]

Ole, I don't have filters so that problem does not concern me. Hardly anyone in Australia uses filters so I am looking at a different way to measure from a base point of a cyclone with no inlet ducting attached and one that has had the ducting installed. It seems to me to be a no fuss way of judging what effect the ducting hood etc have had on air flow. Comments please.

[Michael W. Clark]

Chris,
Ole is right about the filter, but in your situation where you don't plan to use a filter, you could certainly measure airflow on the outlet and compare the readings versus different cyclone inlet conditions and get relative performance. Amp readings are very good indicators, as Ole said, for relative increases and decreases in flow.

One of the reasons we always measured the flow at the fan inlet or collector inlet is because we would take a SP reading at this location too. The SP along with amp readings, temperature readings, and a flow measurement would allow us to evaluate the fan selection versus what the system needs. Often, owners have modified the duct system over the life of the system and it may cause a problem at the fan. If we took the flow measurement on the fan outlet (which we did sometimes due to access and straight duct requirements) we had to go back and take a SP at the fan inlet or collector inlet. There was usually a DP gauge where we could get the collector pressure drop. It doesn't sound like a big deal for the extra readings, but that puts extra holes in the ductwork, and requires additional time.

Mike

[Chris Parks]

Chris,
Ole is right about the filter, but in your situation where you don't plan to use a filter, you could certainly measure airflow on the outlet and compare the readings versus different cyclone inlet conditions and get relative performance. Amp readings are very good indicators, as Ole said, for relative increases and decreases in flow.

One of the reasons we always measured the flow at the fan inlet or collector inlet is because we would take a SP reading at this location too. The SP along with amp readings, temperature readings, and a flow measurement would allow us to evaluate the fan selection versus what the system needs. Often, owners have modified the duct system over the life of the system and it may cause a problem at the fan. If we took the flow measurement on the fan outlet (which we did sometimes due to access and straight duct requirements) we had to go back and take a SP at the fan inlet or collector inlet. There was usually a DP gauge where we could get the collector pressure drop. It doesn't sound like a big deal for the extra readings, but that puts extra holes in the ductwork, and requires additional time.

Mike

Mike, to me that testing description sounds like industrial installations, is that right? As for amp readings my experience up to now is they vary very little but I intend to do some more testing. I think I will go back to no ducting, run it and start adding stuff and take some careful notes.

[Michael W. Clark]

Mike, to me that testing description sounds like industrial installations, is that right? As for amp readings my experience up to now is they vary very little but I intend to do some more testing. I think I will go back to no ducting, run it and start adding stuff and take some careful notes.

Yes Chris, my experience is in industrial applications. Home shop systems are just a scaled down version. I teach a class for ACGIH and we use a 1/3HP centrifugal fan connected to a duct system to illustrate all the concepts and allow the attendees to take airflow measurements. The concepts are the same regardless of system size. Amp draw will vary with flow. You should see a large difference, but it will ultimately depend on the fan characteristics and where you are on the fan curve.

Mike

[Michael W. Clark]

Chris,
How are you planning to measure the performance and are you looking for a relative increase or specific values of ACFM, SP, etc? I was just trying to explain the benefit of measuring the flow at the inlet vs. the outlet based on your initial question. All the outlet will tell you is the flow, the system requirements will have to be inferred based on the fan performance. For example, if you measure the outlet flow based on a particular inlet configuration, you get X CFM. Then change the inlet configuration, measure the outlet flow again, you get Y CFM. If you measure on the inlet of the collector for these two flows and record a SP at the same time, then you start to develop a performance curve. The benefit is that you can measure the SP only and get a good idea of the flow for other configurations. Or, you can design the duct system, calculate the losses, and get a good idea of what the resulting flow would be based on your performance test data. It just depends on what you are trying to accomplish, but flows on the outlet are certainly credible, but may not allow you to predict the performance for other inlet arrangements.

Mike

[Chris Parks]

I am trying to keep everything simple and illustrate to customers a way to measure their systems as installed. I know we can get all technical and install manometers, pitot tubes etc but in the end the customer wants to know what comes out the exhaust is sufficient to do the job. The technical amongst us will decry this approach but from my POV I want to keep it simple for those who are not technical, it is the deeply techy stuff that confuses the hell out of those who are trying top get a handle on all this stuff and that is a fact whether we want to admit or not. BP somewhere in his website says that as a rule any hobbyist size system installed with 150mm/6" pipe hanging off the end of one of his 15" cyclones will work if the installation has followed his recommendations on bends, hoods etc. Now I know this goes against the grain of all those that like to prove that maths are king and you can't possibly do the job without a Cray super computer but we must get to the point of providing a simple way of helping people understand what they have done actually works. In the end if a person follows a recipe of 150mm, no sudden changes in direction, use branches where possible it will work but if they can measure it simply with an aenometer then he can prove his work at the exit point. It is my strong belief that until this stuff is simplified everyone is swimming against the tide and at the same time creating so much confusion that people shake their head and walk away.

[David Kumm]

Chris, I use a fan blade anemometer and measure the velocity and convert to cfm at each machine port and because i run on a vfd I can see the amp draw that corresponds. I adjust the fan speed to acheive a certain flow at each machine and find that two or three setting cover my 20+ drops. Not going to give perfect numbers but close. Dave

[Chris Parks]

David, not meaning to be critical but that is exactly the sort of stuff I want to get away. Most of the stuff in Oz runs on VFD's but all the owners know about them is switch on and hit run as I do all the programming before they get them to keep it simple. I get the same story over and over, this stuff is so complicated I don't know where to start, in fact they are totally bamboozled and it is about time that we who are a bit tech savvy about all this stuff try to find a way to help and by doing that more people will take it up. Does that sound reasonable?

[David Kumm]

Chris, feel free to be critical as I'm anxious to learn. I thought you were looking for ways to measure actual systems in place. For those not technical holding a fan anemometer over the end of the flex that attaches directly to the machine is about as simple as it gets. You want a minimum of 4000 fpm and more is better. I shoot for 6000-7000 fpm with my old machines. I have added the vfd to adjust the cfm but most won't go that step. Dave

[Michael W. Clark]

Chris,
If this is something installed by the OEM, I would suggest either using the differential pressure across the cyclone or the fan motor amps for flow indication.

If this is something installed by the homeowner, then more information would be needed from the DC manufacturer to install something. David's approach is probably the simplest and cheapest with the information available. DC and tool manufacturers could make it simpler, but they don't. (Tell me a minimum SP I need at the machine port for DC, and let this be part of the tool setup.)

I don't think you will be able to meausure "works" or "doesn't work". If you put a 3HP system in my shop, it would be great, but in David's shop it would leave something to be desired. In addition, the definition of "the DC works well" varies among WWs just like opinions about shop layout, tool purchases, finishing techniques, etc. I think your flow indication would need to be relative to the intended performance of the equipment, not whether it "works" or not. At some point in the equipment selection phase, someone (the OEM or the end-user) will need to determine what they need based on the machines they are trying to connect and how far they are located from the DC. This involves CFM and SP whether we talk the actual values or think about it qualitatively.

If the cyclone DP or motor amps appeals to you and you want to set up a test rig, I can give you some advice. I did this for a customer that had existing units with no performance information. You need a duct on the inlet of the cyclone. Don't worry about a data point with no duct at the inlet. You will have to do some testing at some point to confirm the relative flow relationships if this is OEM installed. Once again, this would tell the user where the flow value is relative to the intended design. I'm thinking in terms of a red and green light for indication. If you do actual flow values with a needle, then you would need to tell them where it should operate, but that may be over the person's head you are discussing if they don't want to talk about CFM, FPM, "wg, Amps, etc. Mike

[Ole Anderson]

Chris,

No matter how you do it, they will need some device to measure performance, whether an anemometer, ammeter or a manometer. I suppose the anemometer will give the most direct result once you convert duct velocity to flow rate. Personally I would prefer some type of gauge that was permanently mounted in a convenient location and with a simple conversion curve, would give me an approximation of the flow rate. I would think that an anemometer would be the most difficult to mount and read. If the duct discharges outside, you would need to go outside each time you wanted to take a flow reading. And if you had some sort of a hood on it to keep out rain and critters, you would have to factor that in. An ammeter is good because it could be mounted anywhere, presuming it is not a handheld clamp on style. However you will need to do some calibration with a borrowed anemometer, plotting a curve of amps vs flow rate for the full range of flows, including one point with all gates closed. Opening a large blast gate varying amounts will allow you to obtain enough additional points to plot a curve, measuring amp draw vs flow rate. Three points will be a good start, five would help you dial in the curve accurately. Then you simply post the curve next to the amp gauge. I would think that a manometer calibrated in a similar manner would be even better as the range of readings of the manometer would be greater, beginning at at almost zero no ducts connected and ranging up to 12-16 inches (or equivalent metric for folks on the metric system) at all gates closed and no effective flow. Now a water manometer would be a very low cost option, but a analog or digital meter would allow the gauge to be located in a convenient location. One advantage of a manometer or static pressure (SP) gauge is that you can take the manufacturer's fan curve and simply post that next to the gauge, presuming you have a curve from them you can reasonably trust. Having a anemometer would not be necessary.

[David Kumm]

Where the anemometer helps is with finding the sweet spot when running on a vfd. As you get higher in pressure the amp draw and the velocity or cfm do not increase proportionately. Seems that every type of fan and housing combination has speeds it is most efficient. Sounds more complicated than it is but again a reason for using a vfd. Dave

[Chris Parks]

I think that VFD's are a great device and are the only way that we can rub at 60hz. Running at 50hz entails too much loss.