Dust collector blower mod - anyone try this?

[Alan Bienlein]

So what your saying Carl is that maybe it might perform better with out the impeller overlapping the exit of the blower housing?

[Carl Beckett]

I dont know Alan. If that's been designed with some validated software you should definitely lean towards that. I'm going off old memory from the days of centrifugal pump design, so not exactly transferrable but some basics should translate.

As Michael states, it might be fine to drop velocity a little at the outlet, but I would try not to drop it too much, especially if it then increases when it enters the duct. I would start at the outlet cross section same as the tangent point, and then taper this out to the duct cross section area.

Th fan tip clearance I mean is where the front edge of the vane clears the front face housing. Think of It this way: the inlet is at slightly negative pressure, which is towards the center of the diameter. Then the outer diameter is at max pressure. So a high to low gradient across that impeller which drives 'slippage' of air. A loss. If you tighten down the gap to the front face, less slippage (some small pumps we did we let it ride directly on the front face with a bearing material)

Those closed vane impellers have another dynamic. The od of the impeller is at high pressure. Which makes its way around to the back of the impeller. But if the front of the impeller is open, then a pressure gradient on the front. The net pressure force is higher on the back which creates a thrust force pushing the impeller to the front. Need a bearing that can take this. But closing off the vanes makes the same pressure on front and back, which balances the thrust. But then you need a seal around the intake to again limit the slip loss from the od to the id

It 'might' have a different curve if you close off that overlap a bit. My gut says likely. Although again if you can dial it in to where it just touches the face plate and then back off, that might be a bigger gain

The reason most of these designs don't do these things is pure manufacturing costs and simplification. But this design looks pretty good and there seems to be some real thought put into it, so I wouldn't presume to know how to improve it.

Also, I'm not sure what and increase in current means in and of itself. It might mean its pulling more air. A good thing if efficiency is maintained. So really you need to map some curves (pressure vs flow vs torque/speed ideally) to understand the effect, and also to understand your operating target.

[Michael W. Clark]

The other thing to consider in pressure vs. flow is the diameter and width of the wheel. David was correct in that larger wheels with straight blades tend to handle higher SP better. Also consider the pressure blower arrangement (fans rated in ounces/in2), they have larger diameter wheels, but the wheels are very narrow. They have much tighter housing tolerances, but are also much noisier.

Just a guess here, but I would suspect that the tighter the housing tolerances, the higher the SP you will be able to develop, less leakage. The fan wheel design (blades) are going to have more of an effect on fan efficiency.

Alan, some of the industrial fans and particularly the pressure blowers, have the "overlap" designed so it looks like it would peel the air off the wheel as it turns. In otherwords, the overlap is less, but the outlet area expands after the outlet take-off. I suspect this is to maximize the max SP and may not be for CFM efficiency increases.

The squirrel cage blowers I'm familiar with are for light duty clean air only. They will not develop much SP and any dust will quickly erode the blades.

[Jim Andrew]

The squirrel cage fans in combines are anything but light duty. And they move huge volumes of air to clean the huge amount of grain these machines thrash. What I referred to is the volume of air they move. Combine technology has really advanced in the last few years, each time these machine companys come out with new models, they have considerably more capacity. And it takes a lot of air to clean grain, especially at the speeds these machines move.

[Michael W. Clark]

The squirrel cage fans in combines are anything but light duty. And they move huge volumes of air to clean the huge amount of grain these machines thrash. What I referred to is the volume of air they move. Combine technology has really advanced in the last few years, each time these machine companys come out with new models, they have considerably more capacity. And it takes a lot of air to clean grain, especially at the speeds these machines move.

Jim,
We may have our terms mixed up. This is a squirrel cage wheel as I've seen them.


This one would be a BI type



This one would be a straight radial, material handling




The only squirrel cage fans I have seen in industry are in HVAC systems. They may be on a large hp motor, but if you put any particulate in the fan, you would be lucky if it lasts a month. Maybe the squirrel cage fans are different in combines/agricultural applications. I'm not familiar with the blowers on combines, if they are squirrel cage, then they would have to be much beefier than the industrial versions to handle the material loading.

Mike

Edit, my pictures will not show up. If its squirrel cage type, I would suspect it is cast and that is a different animal than an industrial HVAC version. I would not use an industrial HVAC version of a squiral cage wheel in a material handling situation. JD an Case probably have these wheels cast at a foundry because of the volume of parts. Industrials are custom built and fabricated, wouldn't pay to have a foundy make a one-off.

[Bryan Rocker]

Being a retired jet engine mechanic and well versed in a number of different types of jet engines, I can tell you that the optimum performance when it comes to moving large amounts of air requires tight tollerances. Some of the engines I worked on had as little as .005" of a gap. If I were to suggest design that should work well for this application I would suggest that you look at the J-69 jet engine.

[Carl Beckett]

If I were to suggest design that should work well for this application I would suggest that you look at the J-69 jet engine.

YES!!!! And pictures please!!!

I wonder if a J-69 Jet engine will be adequate air flow for everyone here. I can imagine it would satisfy 'most' of us, but there are a select few that might want more.......

How much back pressure does a cartridge filter add on the exhaust of a J-69 jet engine? Do we have to vent that to the outside? I wonder if my 4" duct will be adequate on the intake. (actually, Im thinking my shop walls might implode....)



But Im with Bryan, tight tolerances means less blow by loss (slippage).

[Bryan Rocker]

When I have more time I will get a better pic. The J-69 produced anywhere from 500lbs of thrust to 1500 lbs depending on the model. While I am not advocating a jet engine as dust collector, I am advocating that the rotary compressor with its inducer disc in front moves air faster and more efficiently than any dust collector currently made. The J-69 compressor is a rotary design and it is very robust and handles unexpected things very well. Take a quick peak at this link....not a good pick of the compressor. I will say that the inducer impellor bolted to the front of the compressor had a diameter of around 12".

http://www.usafa.edu/df/dfan/researc...lities/j69.cfm

[David Kumm]

How well would any of those close tolerance designs work with wood chips passing through them? eventually every cyclone overfills and sends the wood into the impeller. Dave

[Curt Harms]

How well would any of those close tolerance designs work with wood chips passing through them? eventually every cyclone overfills and sends the wood into the impeller. Dave

Use a venturi setup right in back of the exhaust. It the chips & dust didn't catch fire there'd be plenty of air (well, gas) flow .

[Carl Beckett]

. While I am not advocating a jet engine as dust collector, I am advocating that the rotary compressor with its inducer disc in front moves air faster and more efficiently than any dust collector currently made. ".
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Understood Bryan. I was just running with it ..... (and you never know with this group, someone might have one laying out back!!).

To be sure there are better designs for moving air

As for passing chips, the close tolerance I am advocating is between the impeller face and the face of the housing cover. I think here the closer the tolerance, the fewer chip clogs so a win win in this way.

If you wanting it to pass small chunks of wood (I have sucked these up), then of course it has to have a way to get through so again just look at crosss section through the entire flow path.

[David Kumm]

Any ideas on cost? Hobby cyclones are manufactured cheaply to hit a price point. A cyclone designed to more efficiently separate costs several times more but no one seems willing to pay the extra. I'm wondering if there is a market for any improvements that add to cost. Would be great to have some choices though. Dave

[Bryan Rocker]

As to the tolerance of those centrifugal compressors,they are very damage tolerant, the J-69 is rated at around 40K rpm. they have been known to suck all sorts of things and still keep on trucking :0

[Alan Bienlein]

So to get back on track here. Is it possible for me to make a pitot tube out of some 1/8" copper pipe and connect it to a home made manometer? I really don't want to spend the money on a single use item If I can whip up something myself.

I know it won't be calibrated but wouldn't it help to show if the changes I was making where helping or hurting the system?

[Phil Thien]

As to the tolerance of those centrifugal compressors,they are very damage tolerant, the J-69 is rated at around 40K rpm. they have been known to suck all sorts of things and still keep on trucking :0

Agreed. See picture.

jet.jpg