Dust Collector Performance Measurements

[Larry Frank]

Some time ago I posted a question concerning the Oneida “Smart” Dust Collector. The thread received a number of different replies with a lot of suggestions. After reading the responses, I decided that I needed to start over and evaluate what I had and then what I needed.
I read a lot of the posts, read and studied the Pentz information and traded some personal messages with people on the forum. I used some of this information to do some testing on my current system which is a Jet Vortex Collector with a canister filter and has the following specs -

1.5 HP 11” impeller
10.5” Max Static Pressure 1100 CFM with 4” Duct
6” Port – with reducer to two 4” ports


My measurement of static pressure was made using a homemade manometer gave 10.25” and very close to the specs. However, the CFM measured using a digital anemometer gave only about 670 cfm at the 6” port on the collector and about 450 cfm at the 4” port at the collector. This is much less that the spec but not unexpected.

(Note: Using a digital anemometer is not real easy and I moved it around the port and obtained what I thought was representative. Even if I was off several hundred feet per minute, the numbers were still quite low with respect to the specification.)

I also checked the CFM on my ducted system about 10 feet or so away from the collector through a short length of 4” flex pipe and 10 feet of 4” PVC and found only about 268 cfm at 3100 feet per minute. Farther down the line at about 20 feet and through several elbows, I got 216 cfm at 2500 feet per minute.

Bottom line, while my collector gets the larger chips, it does not have the velocity to get the fine particles. I am looking at systems to do this along with increasing my duct sizing to 6”. I will be posting what I intend to do for ducting and also the choices for a dust collector.

It would really be nice if anyone else could post actual data for their dust collection system as a comparison to what I measured.

[Michael Weber]

That CFM seems really low. I would be interested in hearing the detailed methodology of just how you used the anemometer. Also does the anemometer you used measure CFM directly or did you calculate CFM from velocity?

[Art Mann]

I suspect you aren't interpreting the specifications properly. I looked up the unit on the Jet website. The maximum static pressure (10.5 inches) is the resistance at which the dust collector just barely works. I think the 1100 cfm is at 4 inches water column of static pressure, not a 4 inch duct. You can't say anything about the flow rate of a system with a 4 inch hose unless you also specify the length of the hose and how smooth the inside is.

Edit: The only way to measure the flow rate without a hot wire anemometer is to measure the maximum velocity and then apply a derating factor because of surface effects at the periphery of the opening. 80% is a reasonable estimate.

[David Kumm]

Based on my testing using similar methods but with a larger diameter impeller, I think your findings are reasonable. Manufacturer specs are not what you find with real world testing and a working range delivering 1100 cfm takes at least a three hp 14" impeller and perhaps larger if using a cyclone and undersized filter area. Dave

[Art Mann]

The manufacturer's specs and the actual performance of the system may be closer to a match than what you think. What you guys are trying to do is more difficult than you think. You really can't measure air flow very accurately with a little fan type anemometer because you can't get enough measurements in many small locations in the cross sectional area. The air flow near the walls of the duct is only a small percentage of the flow in the middle. This effect is amplified by small duct work. I provided a reasonable estimate based on my experience with high velocity environmental chamber air flow. The other thing is you can't just go by the maximum flow rate. You absolutely must use the performance curve of the machine in operation. Performance varies hugely with different static pressure conditions and a performance curve is the only way to obtain reasonable cfm predictions. You must also have a way to calculate the static pressure resistance of your overall system. In the OP's experiment, he had 20 feet of 4 inch duct work that included several elbows. The SP of such a system is probably close to the maximum 10.5 inch water column at which the machine hardly works at all. His measurements were about right for the system he created.

[Art Mann]

Here are performance curves for a series of dust collectors from a major manufacturer. I just picked them at random. If you can accurately calculate the static pressure of your duct work, then you can use graphs like these to read off the performance with some level of accuracy. On line SP calculators exist but they are fairly complex and require a lot of details to return an accurate number.

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[Larry Frank]

First, thanks to all who have commented and critiqued my methods and data. I started this thread in the hopes of getting some actual performance data and not just the mfg data. Concerning my measurements of velocity....are my measurements real accurate....NO. Are the measurements an approximation of what is going on...Yes. I was looking for a representative reading. If someone has a better method that is reasonably priced, I would be grateful to find out about it. I looked at the costs of using a calibrated pitot tube and digital instrument to get velocity/cfm. The price was way higher than I was willing to spend as I rather spend the $$$$ on an upgrade to my system.

An interesting comparison was made to the Oneida V Series collectors. The black line in the graph is for the 1.5 series collector. It is 1.5 hp with a 12" impeller and a 7" port. The collector lists at about $1500 compared to the Jet Vortex at about $700. The oneida unit also uses a US made Baldor motor.

Oneida does a very good thing as it lists the max actual CFM of 949 cfm at 1.8" SP. It also lists the free fan cfm at 1549 cfm. I suspect that Jet is giving a 1100 cfm at a free fan test and not actual cfm.

One can compare the two collectors and see that there is a pretty big difference in them. I have provided a fan curve from Jet that was in the literature for the Vortex collectors. Given this sample curve, the 670 cfm that I measure at the collector does not seem too far off.

I had some problem interpreting the Jet information concerning what was given as "Air Flow @ 4" (CFM)" of 650 cfm. It does not appear from the curve that the 4" refers to SP as the chart would suggest more like 200 cfm. This is why I interpreted it as at the 4" port. I maybe wrong but all other mfg typically report such data at around 2" SP.

Again, I am asking for people to post some of their actual measurements for their systems. This type of information could be very useful for other in picking a system. While a system may do a good job at getting the larger particles, it is the smaller ones that are a health hazard. In order to collect as much of these fine particles as possible, you need certain levels of air velocity in a system. While, a dust collector may not get all of them, I would like one to be able to get as much as possible.

Thanks

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[John Lanciani]

I've posted this a few times before, but it must not come up in searches so I cut and pasted the important parts;


My dust collector is an Oneida V3000. It is a 3hp system with a 14.25” backward inclined cast aluminum impeller and a HEPA filter. The filter is well seasoned and was cleaned prior to the testing. Ductwork is 6” PVC.
I used the following test equipment; UEI EM151 digital manometer, and a Dwyer 471 hot wire in duct anemometer.
The Claimed CFM numbers are extracted from an Oneida published system curve for the V3000. SP measurements were taken just before the cyclone inlet. Air velocity measurements were taken from the longest straight piece of pipe in my system, following Dwyer’s guidelines as closely as practical. All FPM measurements were rounded down to the nearest 25, and I used a divisor of 5 to calculate CFM from FPM. Since the accuracy of the Dwyer 471 is +/- 4% I didn’t feel compelled to calculate to the exact decimal.

The results were as follows;

SP -Claimed CFM -Measured FPM -Calculated CFM
12.4------100--------------375------------------- 75 (this number reflects my system leakage)
12 --------200------------- 925------------------ 185
11-------- 400------------ 2050------------------ 410
10-------- 525------------ 2950------------------ 590
9 ---------650------------ 3700------------------ 700
8 ---------775-------------4050------------------ 810
7 ---------900------------ 4550------------------ 910
6-------- 1000------------ 5100----------------- 1020
5-------- 1100 ------------5450----------------- 1090
4 --------1200------------ 6100----------------- 1220
3.8------ 1250 -----------6200----------------- 1240 (this is with all gates open on my system)

[Larry Frank]

Thanks to John Lanciani for reposting his data. It is quite interesting that his calculated CFM and the claimed CFM are so close together. Also, the information on the instrument used to measure the CFM. I had not considered this instrument which is around $350.

[Michael W. Clark]

Larry, an inexpensive flow set up is a mini pitot tube and Dwyer magnehellic gauge. Mini Pitot tube is about $50 and the gauge is about $60. Get a 0-2" gauge. Pick up some rubber hose and hose barbs at the hardware store. I think they are 1/8" NPT on the gauge.

You will be reading velocity pressure. This converts directly to velocity using the right equation (V=4005 x VP^0.5). Calculate velocity for each reading across the face of the duct and average them. Then it is Q= velocity x duct area. This is why John was dividing by 5 to go from velocity to CFM. A 6" duct is 0.196 ft2 which is ~1/5.

I've done hundreds of pitot traverses (maybe more) for a living, its the best suited and most accurate way to take flow measurements.

[Ben Rivel]

GREAT info in this thread! Thanks you guys!

[Larry Frank]

Michael Clark.....can you provide some product numbers for the items you mentioned?

Since many of us have not done this or seen it down, could you provide some pictures and more explanation of how to actually do it. I think that there would be interest in this method.

Than k s for the info.

[David L Morse]

If you're willing to make your measurements in the middle of a length of duct you can use a simple homemade pitot tube and your homemade manometer to get some decently accurate data. Post #79 in this thread (http://www.sawmillcreek.org/showthread.php?197861-How-to-measure-dust-collector-performance) shows how I did it. Post #73 shows the data I got for a DC similar to yours (the infamous Harbor Freight unit).

Also in post #73 is a chart showing motor current versus CFM. Using that chart I can now determine the flow in my system by merely checking motor current, no need to drag out the manometer or stick my pitot tube anywhere. This has been very useful.

[Michael W. Clark]

Michael Clark.....can you provide some product numbers for the items you mentioned?

Since many of us have not done this or seen it down, could you provide some pictures and more explanation of how to actually do it. I think that there would be interest in this method.

Than k s for the info.

Here is the gauge http://www.dwyer-inst.com/Product/Pressure/DifferentialPressure/Gages/Series2000
Here is the pitot tube http://www.dwyer-inst.com/Product/TestEquipment/PitotTubes/Series160#ordering

2002 on the gauge
167-12 on the tube

This is a quick starting point for how to take airflow measurements with a pitot tube. I'm sure there are better articles but this is the first one I found. Let me know if you have any questions and I'll be glad to answer.
http://www.trutechtools.com/Measuring-Airflow-with-a-Pitot-Tube_c_253.html

[Alan Bienlein]

Here is a link to the thread but I'll post my measurements here. http://www.sawmillcreek.org/showthread.php?213202-Preliminary-test-measurements-on-my-dust-collection-system&highlight=With all the discussion on dust collection systems lately I figured I would take John Lanciani up on his generous offer of borrowing his test equipment. He sent the following test equipment for me to take readings on my home built Pentz design cyclone.

Dwyer 471 hot wire anemometer, a UEI EM151 digital manometer, and a basic analog clamp-on ammeter but I substituted my Sperry digital clamp on amp meter.

My system is home built from plans on Bill Pentz's website. It is a 20" diameter cyclone with the Leeson 5 hp motor turning a 16" backward incline steel impeller. It has a 5" x 10" rectangular intake and exhaust into 2 seasoned Wynn 9L300 filters. I did not clean the filters before taking these measurements.

Here are a couple of photos of my setup. I put numbers on each drop to make it easy to follow exactly what part I am testing.

This picture shows where I connected the manometer and the hole circled in red is where I inserted the hot wire anemometer.
http://www.sawmillcreek.org/attachment.php?attachmentid=280836&d=1390758994&thumb=1 (http://www.sawmillcreek.org/attachment.php?attachmentid=280836&d=1390758994)

Here are the pictures with the corresponding numbers for the test. All measurements were taken in the 8" duct and opening and closing the blast gates on the various branches. Talking with John he said to divide the FPM by 2.85 to get the cfm.


http://www.sawmillcreek.org/attachment.php?attachmentid=280838&d=1390759004&thumb=1 (http://www.sawmillcreek.org/attachment.php?attachmentid=280838&d=1390759004)http://www.sawmillcreek.org/attachment.php?attachmentid=280837&d=1390758999&thumb=1 (http://www.sawmillcreek.org/attachment.php?attachmentid=280837&d=1390758999)

Blastgate-----SP-----FPM------CFM------Amps---------Tool

All closed-----14.9"---700------245-------11.8---------None

All open-------3.6"---6250-----2192------18.5----------All

#1-----------10.9"---3400-----1192------16.5---------SCMS

#2-----------11.5"---3125-----1096------16.3--------8" jointer

#3-----------12.4"---2900 ----1017------15.6--------Ridgid TP1300 Planer

#4-----------6.21"---5600-----1964------17.9--------End of duct work

#5-----------10.2"---3600-----1263------16.9----------Table saw

#1 & #5------6.51"---5200-----1824------17.8--------Table saw & SCMS

#2 & #3-------8.3"---4300-----1508------17.4--------8" jointer & TP1300 Planer


These readings are with the machines connected like they are normally used. Number 4 is an end of duct run that I thought I might use one day to expand.


I do want to plot a graph of SP and CFM for my system but want to make sure I do it correctly so I don't waste my time repeating it so any help would be appreciated.

[David L Morse]

Alan, here's what I get when I plot your data:
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I left out the all closed data point, it looked a bit odd.

[Joe Jensen]

I didn't get the anemometer to determine the exact fan curve but rather to measure objectively relative changes. The engineer in me spent a couple of hours last reading and considering installing a pitot tube and gauges. Then I realized that I just need to measure to see in changes help or not.

[John Lanciani]

One piece of advice for anyone who is looking for test equipment is to keep an eye on eBay. I got my Dwyer hot-wire anemometer for under $100 in as new condition. There are still deals to be had if you're patient.

[Scott DelPorte]

I took a little different approach to computing the CFM for my dust collection system. My dust collector is in a separate room adjacent to the shop with the air returning through a grate. The grate manufacturer publishes the pressure loss through the grate as a function of CFM. So I connected a magnehelic gauge to measure the static pressure difference across the return grate (between the room with the collector, and the shop), and then computed the overall system CFM based on the grate's loss curve from the manufacturer. A manometer would have worked instead of a magnehelic, but it just seemed easier for my eyes to read off the needle on the gauge.

[Michael W. Clark]

A magnehellic setup to read static is ideal for monitoring changes. Connect one port to the duct and leave the other one open. A change in flow give a large change in static because the SP varies with the square of the flow change. You probably want at least a 0-10" gauge, depending on your collector and system.