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Cyclonic Dust Separation – Overview

How does a cyclone work?

Essentially the function of a cyclone separator is to remove the majority of the dust and debris that you suck up, and separate it out from the air stream that carries it. It does this by introducing the dust filled air to the cyclone chamber via an inlet mounted tangentially to the cylinder at the top. This causes the air and dust to circulate around the outside of the container, and as such centrifugal forces keeps the particulate mater to the outside edges. The ‘air ramp’ forces the air stream and dust particles down into the conical shaped container where the cone shape creates a cyclone with higher centrifugal air speed.

If the cyclone works well, the higher air speeds in the cone will throw the dust particles, both large and small, off to the side. Finally, near the bottom of the cone the air reaches a ‘turn-around point’. This is the crucial point when the clean air changes direction, hopefully leaving behind the particulates that it was carrying, and goes up the centre of the upper cylinder and off to the vacuum cleaner. The dust, by virtue of its inertia (and to some extent gravity) continues on down, falling into a large settling chamber where the air is almost completely still. Thus, in a helter-skelter stylee, dust goes down the chute, while the clean air moves away up the central inlet to the vacuum.

In short, the cyclone prevents your filters from clogging with dust particles, preventing the loss of suction that most casual DIYers experience when they hook up their houshold vacuum, or even their dedicated shop vac to a woodworking tool.  For a quick look at how cyclones work, play this video of my first prototype, having its test run.

What cyclones are not:

So called ‘cyclonic dustbin lid’ separators, like this, work ok for what they are, but would actually be more accurately marketed as drop boxes.  As with many upright vacuum cleaners that call themselves things like ‘cyclone power daemon’ they suffer the same few major problems: the ‘cyclone’ is not actually a cyclonic separator at all, just a drop box that happens to swirl a bit, and/or that the cyclone assembly is not separate from the collection point, so while air swirls, it is not necessarily a good thing because it disturbs any collected dust, which is thus likely to be sucked up into the extractor where it clogs the filter or, if small enough is thrown back out into the atmosphere – cough cough!

This double cyclone build:

real cyclonic separator, does just that, it separates off the dust into a separate holding chamber, where the air is relatively still and the dust can settle.  In these pages we consider the cyclone in a number of parts:

  • The upper body – the part that is simply cylindrical in shape and provides a mounting for the air inlet and outlet.
  • The cone – the section that is cone shaped (surprise surprise). It channels the dust down through the dust chute (on the end of the cone) and into the collection chamber.
  • The air inlet and ramp – the inlet brings in the dust filled air, the air ramp reduces turbulence by directing that air downwards into the desired spiral.
  • The air outlet – is another cylinder that sits in the centre of the upper body. The clean air is sucked out the air outlet.

I wanted to make the cyclone clear, so we could see what was going on inside. This was important to me, because despite the amount of reading I have done around the subject, cyclonic filtration still seems a bit like black magic to me and I wanted to watch it actually happening in detail. Having it transparent also means I can observe the performance differences when I tweak the design, change the airflow, or vary the waste matter being separated. Plus we can instantly see if the collection chamber is full or if there is a blockage or a similar problem.  Basically having it clear is just a lot cooler!

The cyclone is based on an ‘upper:cone ratio’ of 1.64 (the length of the cone is 1.64 * the diameter of the upper section), which has been shown to work very well. If you are making a cyclone out of sheet steel Bill Pentz’s fantastic excel spreadsheet can scale the design and calculates all the dimensions for you. I experimented with different materials so the actual construction varied substantially, because I wanted to see through to the inner workings. Still, the spreadsheet provides an excellent starting guide if you want to use steel- you can download and checkout the spreadsheet here (it is near the end of the page). If you want to replicate the DS cyclones, you don’t actually need it because for each step I have included all the measurements in SketchUp diagrams (if you want to download the actual SketchUp files they are included in the Resources and References step at the end). Either way, if you are considering any kind of dust related antics I recommend you check out his site, there is a real trove of information there.
The two good features of Pentz’s design, other than the upper:cone ratio, are its tall and thin rectangular section sloping inlet, and air ramp.  Both of which help to direct the air stream in a turbulent free way into that characteristic desirable helter skelter shape.  Pentz says that using such a cyclonic filtration system:

Even shops that make multiple 55-gallon drums of MDF dust daily find they can go six months and still see almost no fine dust in their filters. The same is also true in terms of scaling this design to much larger. I designed one of these for a huge cement processing facility and they went from having to replace filters monthly to every five to six months, plus were able to use a much smaller horsepower motor.” (Bill Pentz)

For the dust sniper, we need to consider how this will integrate with the rest of the system. I made two cyclones. Why? Because that way we can keep the airflows of the two vacuums we use separate. Separate airflows gives us more flexibility, it means we can store different waste materials in separate containers – useful if you plan to re-use the sawdust or wood chips for anything (like composting or PVA-wood dust casting). It also means we can use one or both vacuums at once depending on the extraction requirements at hand. I have had good results, for example, using both at once to extract dust from a bandsaw (from modified collection points), where as a lot of of my tools are quite happy with one vacuum going (no sense having two going if we can do a good job with one right?).

This is Mk1 in action almost ready to be integrated into the Dust Sniper project.

Previous Cyclone Step Next Cyclone Step

Responses to Cyclonic Dust Separation – Overview

  1. Matas

    Well, seeing you have this layed out so simply for us to grab, i would only kindly ask where is the Resources & References page you refer to. Since there is only a question WHEN will i be doing this, not IF, that page would be most beneficial :)

    Thanks

  2. Bongo

    Hi Matas,
    Thanks for pointing this out. The page you are looking for can be found here ttp://www.floweringelbow.co.uk/projects/the-cyclone-dust-separator/resources-and-references/
    You can also see some of the rest of the dust sniper details here.. The ‘dust sniper’ is the whole unit I ended up making, which included the two cyclone separators described here on Flowering Elbow.

  3. Nate

    Hi there — I love your projects: cleverly conceived, expertly done, and well documented.

    I have closely studied your Dust Sniper project and am marveling at all of the different components/strategies you included in the single design (cyclones, dampening, tortuous path, etc, etc, etc…). Very comprehensive!

    I wonder if you’d give me your opinion on which sound suppression techniques you’d consider most effective and applicable to my situation? I build guitars in my basement workshop and noise and dust control are high priorities inside and outside the house. I modded a standard two-bag dust collector to use a Thein baffle separator (http://www.cgallery.com/smf/index.php?topic=251.0), and I vent the exhaust air outside.
    The link shows the project in the early stages; I have since dialed in the dust collection performance so that the exhaust air is very clean. The problem I’m trying to solve now is the noise – inside the shop and especially outside where the exhaust vent is positioned within earshot of several neighbors. The exhaust transitions from the blower to 6-inch round HVAC metal duct (about four feet long with two 45-degree bends) and then to a 4×10-inch exhaust port with a sheet metal weather flap. The noise escaping is quite loud outside. I am considering making improvements in stages to see what helps, and I would greatly appreciate any suggestions on what to try first.

    Options before me could include 1) adding something after the exhaust, 2) modifying the airstream inside the shop, 3) building an enclosure around the existing set-up, all the way up to 4) building an elaborate enclosure outside that contains the machine and exhaust path. I am hesitant to start with option four because of time/money/space constraints. Any advice? I’d be happy to provide any detail photos if your are interested.
    Thanks loads, Nate, OR US

  4. Bongo

    Hay Nate,
    I let this one slip and just re spotted it, so sorry for the delayed reply…
    Has the situation changed? Have you implemented anything?

    I would probably be tempted to try option 1 first. Use a cardboard box, cut a few flaps in it (don’t actually remove any material, just cut slits and fold them out so the air can get out) and try sticking it over you exhaust outside. Try with different size boxes, it’s an easy way to see whether just adding a little enclosure at the exhaust is going to cut it. If it sounds promising with the cardboard, build a weather proof box – mdf is good (though obviously needs weather protection), a big slate on top would help too. You can expect this to preform quite a bit better than the cardboard of course… Lots of options…

    Hope that helps, let me know where your at.
    Cheers,
    B.

  5. Doug T

    Do you know the effects of the dirty air being forced into the cyclone as opposed to a normal set up of the cyclone being under vacuum. In otherwords, the fan is upstream of the cyclone instead of downstream.

  6. Bongo

    Hi Doug,
    Obviously this wouldn’t work with a vacuum cleaner or shop vac, but if your using a material handling impeller from a ‘dust collectors’, then yes that works.

    In that instance there isn’t much difference in the way they would function either way. Lots of people like the impeller after the cyclone so that if they accidentally suck up big objects like a small spanner, it wont go straight to the impeller and get stuck/ cause damage. But most material handling impellers can deal with the occasional blunder, and you can add a wire grill at the impeller inlet if worried…
    Personally I would still go for positioning the impeller after the cyclone, for extra protection ;)

  7. hemant

    hi sir,
    i want to make cyclone with filter bag as my project for woodworking saw dust,
    here i calulated the outside diameter of cylone is 300mm. and inlet hose is 5″*5feet long,
    so the 1HP motor will be sufficiant for my cyclone separator…. if not then suggest me as early as possible…

    thanking u…

  8. Ian

    Hi Bongo,

    Very inspired by your research and methods. I’m sourcing out the materials to make my own but there is one thing I’m confused with. This could be obvious.

    ‘The cyclone is based on an ‘upper:cone ratio’ of 1.64 (the length of the cone is 1.64 * the diameter of the upper section)’

    does this symbol mean multiply (*) or is a ratio 1 to 64?

    Also would you say that your measurements for the cyclone is good for an orbital sander? Or will it need to be bigger?

    Thanks

  9. Bongo

    Hi Ian. Thanks for the comment. It is a ratio that refers to the cone dimensions – the height of the cone is equal to the diameter at its widest point (in this case the top) times 1.64.
    So for example a small cone for vacuum cleaner might be 150mm in diameter at its widest point (which is also the diameter of the upper body of the cyclone), so the length of the cone would be 150mm x 1.64 = 246mm.
    Hope that helps?

  10. Ian

    we are using a pre filter before getting to the cyclone so can I put the fan and motor before the cyclone and push the air into it, or do I need a vacuum to suck the air out of the top of the cyclone

  11. Bongo

    Hi Ian – Yep, you could push through the cyclone in that case.

  12. Toby

    I have a large dust collector(cyclone style) recently it started blowing all the wood dust out the exhaust. I emptied the collection barrel and made sure the blast gates are open and the cone is clear. When they run the system it blows everything outside. How can I fix this?

  13. Bongo

    Hi Toby,

    It is hard to de-bug your system from afar, but if you are still getting enough airflow, and all the pipes are clear and the collection bin has plenty of room left, it sounds like you might have an air leak somewhere (between the collection bin and cyclone maybe?).

  14. Ken

    Hi, I’ve just come across your site and have been reading up on the cyclone and the related links you have posted. All looks good and I’m with you all the way about the requirements etc to get this to work efficiently and to all possible extents quietly. Have a look at the link here; http://billpentz.com/woodworking/cyclone/index.cfm

    This gut has on his site explanations, the theory, the maths and everything else with regards to cyclones and the required fans to move the air in sufficient amounts to be effective and afficient. The site also lets you use any of the information available there to download and use at your own discretion so long as its not for profit, this includes plans that will change as per your specifications, ie, air flow rates, hose size, blower size (and this includes a vacuum cleaner as the blower) etc.

    There is a lot of reading there, but we all know there’s no such thing as a free lunch, there is always some work involved somewhere.

    Have a look and keep up the good work.

    Ken

  15. Bongo

    Hi Ken,
    Thanks for the comment. Yes Bill’s site is amazing. Don’t worry I have read through it many times! Most of the dimensions and math theory for the cyclone here comes from his research findings – you will see links to his site scattered amongst these pages.
    In fact the only really interesting thing about this build over ones already documented on Bill’s page is that it is targeted at shop vacs rather than large dust collectors, and the use of clear material rather than sheet metal. Oh and an unusual emphasis on making it quiet.

    So yeah, Bill’s stuff rocks, everyone should check it out.

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