Cyclone dust collector blower position

[Carl Beckett]

Its hard to imagine this hasnt been covered already, so just ignore if so.

But shouldnt the blower go BEFORE the cyclone, and not after?

Blowers can push more than pull, so any pressure drop through the cyclone would be handled better by putting the blower in between the equipment and the cyclone (and as close to the machine as possible - to where it 'T''s off to other machines) - to put as much of the pressure drop on the outlet side of the blower.

(yes, there is convenience of mounting the blower right to the cyclone)

I wonder how much effect this would have? Maybe the cyclone itself is negligible pressure drop?

[Michael O'Neill]

It can be done..... But do you really want all the chaff going through the blower??? If it gets ahold of a big knot or a tool of some kind, it could-most likely would, damage the impeler.... Imagine a tape measure passing through the blower........

Might not be to good for the tape.....


Michael

[David Kumm]

It can be done..... But do you really want all the chaff going through the blower??? If it gets ahold of a big knot or a tool of some kind, it could-most likely would, damage the impeler.... Imagine a tape measure passing through the blower........

Might not be to good for the tape.....


Michael

They are made both ways. Alan Schaffter has a push through. Performance doesn't change all that much and there are likely a million other factors that you would have to get exactly right for the difference to be apparent. If you look at the Aget systems with the impeller set along side the cyclone you will have a push through. Dave

[Clint Olver]

A proper cyclone can suck up a 25' tape measure. I wouldn't want something that size hitting the impeller. For that reason alone, I'd put the blower AFTER the cyclone.

C

[Bruce Wrenn]

First I don't put tape measures in my DC system. (I don't flush golf balls down my commodes either.) A blower can "push" no more air than it can "suck." As for trash though impeller, most if not all, two bag systems are through the impeller first. Manufacturers figured out early on that some one is going to suck stuff up that isn't chips or fines. That is why inlet side of impeller blades are tapered, plus they usually have those "cross hairs" in the inlet to stop large items from entering blower. A simple "drop box" could take care of large items. It could have inlet and outlet straight across from each other to reduce suction losses due to changes in direction.

[Michael W. Clark]

This premise is not true. A fan does not push more than it pulls. What goes in the inlet, comes out the outlet. The fan is on the outlet so it handles minimal material. When mounting a fan on top of a cyclone, make sure it is rotating the proper direction, or your air volume will be reduced.

Mike

[Carl Beckett]

Ok.... as much as I dislike starting another DC question thread - here it is:

Does anyone know of a good (meaning cheap/simple, without use of a hot wire anemometer) way to measure air flow?

I would like to test some different configurations - with the hope of increasing air flow and improving separation of the cyclone. (at least my thinking is that the system can benefit from better (higher) air flow - the cyclone isnt doing a great job at separation)

(although this rotation effect has me wondering.... I dont have it mounted on top, but there might be an effect going on there so that another consideration)

In trouble shooting mode.

[Bruce Seidner]

you can buy or make a water manometer.

I did a quick Google and found this: http://www.obairlann.net/reaper/motorcycle/manometer.html

[David Kumm]

you can buy or make a water manometer.

I did a quick Google and found this: http://www.obairlann.net/reaper/motorcycle/manometer.html

I use a fan blade hand held anemometer. You can find them for $75-125 and well worth it to know what velocity you really have at each machine port. The only cfm or velocity numbers that mean much are measured at each machine. Get the type that allow for speeds of 6000+ fpm so you don't shatter the blades. I try to be consistent and hold it against the edge of the flex or fitting and if larger than 5" you need to move it around the opening and average out the readings. If I read from 5100-5500 on a 6" port I assume the flow to be 5200 and do the math to convert to cfm. You don't need absolute numbers here but a range that you can convert. You will find that the ports closest to the cyclone read higher than those farther away and a pattern develops that allows you to judge how the bends and pipe affect velocity. I found that I could pull the same velocity through a 7" pipe that I could through a 6" which increased my cfm by about 1/3. You do need to measure amp draw as well to determine whether you are running the motor at capacity as the gates open. Dave

[Alan Schaffter]

They are made both ways. Alan Schaffter has a push through. Performance doesn't change all that much and there are likely a million other factors that you would have to get exactly right for the difference to be apparent. If you look at the Aget systems with the impeller set along side the cyclone you will have a push through. Dave

Yup, as David says, I've been doing that for over 10 years. While I haven't intentionally tested my fan/impeller I have sucked up many chunks of wood, and yes, at least one tape measure and a DP chuck key, with no detriment to my 14" steel impeller.

Unlike water pumps some of which push better than they pull, our material handling DC blowers work the same both ways.

http://www.ncwoodworker.net/pp/data/1329/medium/P10100382.JPG

[Michael W. Clark]

For airflow measurements, try a Pitot tube and manometer if you don't want the anemometer. Dwyer Instruments has some of this stuff that I have used. There may be some other places that have something similar, but cheaper.

Dwyer Pitot Tube #166-12 http://www.dwyer-inst.com/PDF_files/124.pdf
Dwyer manometers http://www.dwyer-inst.com/PDF_files/430.pdf
Instead of the manometer, you could use a magnehelic gauge http://www.dwyer-inst.com/PDF_files/2000.d.pdf If you are only doing flows, get the 2002AV with the velocity scale. If you want to measure SP, then maybe 12" range or whatever you think your collector can develop. A lot of people use two gauges, one for flows, the other for SP measurements.

[Carl Beckett]

Thanks for all the ideas (simple home made manometer is more my speed(budget))

The basic problem is this: I purchased a Clearvue cyclone and connected my current 2hp blower to it. The separation is not good (I think it may be inadequate air flow - just too low!). I do have a lot of 4" pipe, including substantial flex tubing (all stuff I got for free)

I took a chance on trying to get all the free stuff working before going out and spending another $1000 on a 5hp, 15" impeller and 6" ducts everywhere. I dont need perfect separation (I do vent to the outside), but its pretty dismal at the moment and not adequate at the tool anyway (all my tools have 4" ports, and upgrading these would not be trivial - but I would do this if it allowed the current blower to work).

Yes I may be fighting a no win battle, but its a tricky (and easily philosophical) topic. I want to see just how close I can get with the current equipment at hand (currently unacceptable, so wanting to learn if I can upgrade it to acceptable status). Maybe start with a very minimal run of pipe and if that doesnt do it then nothing will. (the bare blower/clearvue combination). The clearvue gets good reviews so I know its possible, but I havent found any direct data on how the clearvue does with low flow rates.

[Alan Schaffter]

Cyclones are sized to the blower. 2 hp with what is likely a 12" impeller is not sufficient to properly drive a ClearVue.

[Carl Beckett]

Cyclones are sized to the blower. 2 hp with what is likely a 12" impeller is not sufficient to properly drive a ClearVue.

I think this is the fundamental problem. ( kinda thought was up against some fundamentals)

I do think the impeller is 12" ( or maybe 12.5.... But definitely not 15)

Hmmm.... Might have to back up a bit and look at choices of a different cyclone, or different blower ($$$)

[David Kumm]

don't spend money on a different cyclone. You need to look for a 3 hp blower with a 14" fan or something like the clearvue 5 hp 15". Look at Pennstate as well. they have a 3.5 blower unit that would fit as well. Dave

[Michael W. Clark]

Thanks for all the ideas (simple home made manometer is more my speed(budget))

Carl, you can definitely build the manometer, but not sure how you intend to measure flow with it? You could measure SP and know that if you increase your fan flow, and the system does not change, you will see a higher SP at the fan inlet. I may be mistaken, and it won't be the first or last time, but my experience is that manometers only measure differential pressure, they do not measure flow or velocity directly. You will need a pitot tube, orifice, or some device that creates a certain DP that corresponds to a CFM.

It sounds like you may have an undersized fan. Low flow through the cyclone has a dramatic effect on efficiency. This is where it would be nice if manufacturer's would at least give you a cyclone DP at a given CFM. If you had this information in your case, then the water manometer could be used to measure DP across the cyclone then calculate the resulting CFM. Maybe Clearvue would give you this? The other thing you can do is measure your fan motor amps. If they are pretty much maxed out (approximately equal to FLA on the fan motor nameplate), then you probably have too small of a fan. If the fan amps are low, then either the motor is oversized or you have a flow problem caused by your system.

Its tricky to trouble shoot a system when manufacturer's don't provide any performance data. How do you know when it is working like it should? I would start with checking the fan amps if you have an amp meter.

You probably don't need to build the manometer for 96" of DP. My guess is that you would have a max of 10-12" at the cyclone inlet. If you build it for 24", that should be plenty.

[Carl Beckett]

Carl, you can definitely build the manometer, but not sure how you intend to measure flow with it? You could measure SP and know that if you increase your fan flow, and the system does not change, you will see a higher SP at the fan inlet. I may be mistaken, and it won't be the first or last time, but my experience is that manometers only measure differential pressure, they do not measure flow or velocity directly. You will need a pitot tube, orifice, or some device that creates a certain DP that corresponds to a CFM.

It sounds like you may have an undersized fan. Low flow through the cyclone has a dramatic effect on efficiency. This is where it would be nice if manufacturer's would at least give you a cyclone DP at a given CFM. If you had this information in your case, then the water manometer could be used to measure DP across the cyclone then calculate the resulting CFM. Maybe Clearvue would give you this? The other thing you can do is measure your fan motor amps. If they are pretty much maxed out (approximately equal to FLA on the fan motor nameplate), then you probably have too small of a fan. If the fan amps are low, then either the motor is oversized or you have a flow problem caused by your system.

Its tricky to trouble shoot a system when manufacturer's don't provide any performance data. How do you know when it is working like it should? I would start with checking the fan amps if you have an amp meter.

You probably don't need to build the manometer for 96" of DP. My guess is that you would have a max of 10-12" at the cyclone inlet. If you build it for 24", that should be plenty.

Thanks Michael,

I was simply going to chase around the piping with the manometer, to get an understanding of the relative restrictions. If there was a particular segment that was creating a high pressure drop, I would first focus on that.

I dont have a good amp meter for those currents.

Kinda shaking my head about all this (and will admit up front that I want to cheap it). But by the time I buy an amp meter, a anemometer, and a dust particle counter - all for the purpose of analyzing/designing the system - there is no $$ left to purchase the actual equipment.

Im understanding more why some choose to just get a really big blower, attach really large dia ductwork, and be done.

[Michael W. Clark]

Yes, take a SP at multiple places and look for anything abnormal. This is what we would do when trying isolate a section of duct that may be plugged. You can drill small holes in the duct and cover it with tape.

[ian maybury]

There's a mountain of truth in what you said Carl: 'Im understanding more why some choose to just get a really big blower, attach really large dia ductwork, and be done.'

Not only does marginal CFM leave you struggling to get even decent chip collection, it also means that (if you do manage to find the sweet spot where it will work) that quite small changes in resistance caused by filter blinding and that sort of thing have a disproportionately larger effect than is the case with a larger diameter impeller which gives not only higher CFM but also has a lot more pressure capability....

It's possible too to build a system using larger capacity stuff for not a lot more money if you put the time into digging up used or discounted stuff too.

I don't mean to brag - but honestly: moving from a 1kW mobile bag filter to a Pentz style 160mm ducted/16 in impeller has been such a breath of fresh air. All of the fuss, bother and pernickedtiness just falls away. It works so much better even on stuff like a router table that doesn't seem to need so much airflow. The Incra port is only 2 1/2 in, and airflow through the fence is fairly restricted - as is often the gap down through the router plate around a cutter.

It doesn't really matter though, because the extra pressure/suction the big impeller delivers means it's pulling a lot more CFM than it would on more typical systems - and even at that there's more than enough spare puff to run a supplementary 4in flexible with an intake hood that can be placed where needed...

ian

[Michael W. Clark]

I definitely agree with Ian. There are not many situations in woodworking dust collection systems where more CFM hurts. DC is getting to be more like other tool purchases (if not already) where you may try to buy the best you can afford at the time. The newest may not always be the best. If you come across a good buy on a used cyclone and fan, then add a good after filter, you would likely be better off than buying a new single stage system. Sure, you will have some time configuring the used equipment like you want, customizing the setup to get the dust drum out, etc. However, you will have less time invested trying to squeeze every CFM you can out of an undersized fan or system.

But homeowners are not alone in this, many industrials try not to spend money on dust collection. I worked the past few years for a company where we mostly tried to improve DC systems that were undersized to start with. Sometimes the owners were willing to invest in major modifications, but most of the time, they wanted to optimize their existing system and make comprimises.

[Eric Tyira]

I'll add that the air going into the blower is at standard conditions (normal temps, sea levels, etc.) while the air coming out is compressed. That's why the "push" from the blower feels like more air than the intake. It's the same amount of air molecules being moved, just more compacted on the outlet side.

[Michael W. Clark]

Yes there is a slight density difference on the inlet and outlet due to the difference in SP. However, the "push" you are feeling is a pressure known as velocity pressure. Velocity pressure can be equated to duct velocity, this is how a pitot tube is used to get duct velocity and then CFM (knowing the duct area). Its the same force you feel when you stick your hand out the open window of a moving car. If your air velocity is 4000 FPM on the inlet and outlet, you will feel basically the same "push" in both ducts.

On the inlet of an open duct, velocity goes down drastically as you move your hand away from the duct. This is mostly due to the fact that the open duct is drawing air from all directions, i.e. front, back, side, behind it if possible. On the outlet, all the air is basically moving in the same direction, out. This is the premise for the "straw example" to illustrate how close your hood needs to be to the source to capture the dust. The better your hood design, the less wasted air being pulled from around the hood, and the more air being pulled from the dust source.


Mike