Pellvac virvelvind (whirlwind)

[jalar]

Hi, thanks for making the plans available to us all. I was thinking to build this for myself but found http://www.pellvac.com/s/askcyklon.php. Different, but similar. It isn't cheap, though. Apparently from the 70's, see http://www.pellvac.com/pdf/artikel%20uppfinnaren%20och%20konstrukt%f6ren.pdf. Now, to the question: The aperture is much larger in the whirlwind, and has no solid part. What difference does this make, if any?

[phil (admin)]

Hi, thanks for making the plans available to us all. I was thinking to build this for myself but found http://www.pellvac.com/s/askcyklon.php. Different, but similar. It isn't cheap, though. Apparently from the 70's, see http://www.pellvac.com/pdf/artikel%20uppfinnaren%20och%20konstrukt%f6ren.pdf. Now, to the question: The aperture is much larger in the whirlwind, and has no solid part. What difference does this make, if any?

I think the battle with that unit would be that it would only marginally improve scrubbing.  The aperture is just too wide and as the unit fills, too much stuff is going to make it through to your filter.

If you notice, there is a line on his bin, the "fill-line."  Anything above that will probably just make it to your vac.

If you watch the entire video, at the end they remove the bag from their vac, but they're careful not to tip or shake it.  And it seems to have some weight to it already, too.

[jalar]

They do list their separation to be 99% so I'd expect some dust to make it to the bag, yes. But they claim it is efficient for fine dust too. What is the efficiency of your construct?

[alan m]

jalor
i dont know the efficiency of phils design . iv ran mine with no filter(will be vented outside) for a while (i am only setting it up)
i dont notice any dust  in the shop (other than what was already there)

i put some ploistyreen into the pipe to see what would happen.
it was all seperated . . there was none anywhere esle . i was expecting a shower of balls but nothing

just because they say 99% efficient doesnt mean anything.
they are bount to say that. i would like to see a review by a trusted reviewer


i like the look of that seperater.
its a shame the top part isnt the size of the whole lid. it would probably seperate better
the baffel plate part is easily fixed

[jalar]

I suspect a larger radius would make it worse for the fine dust. There are larger versions, for "industrial" use, biggest tank they use is 25 cubic metres  8). Pellvac's own use is for ash and wood-pellet dust in their vacuum wood-pellet-handling system, so it is aimed for fine dust, not coarse.

They claim 99 percent for talcum powder, I'd expect larger chips to be better separated. There is a video on youtube where they use it on wood-pellet ash: 1 kg of ash through the thing, and 8 grams make it through. There is also a referece to a test at Chalmers (technical university), but I have still to see the report.

I do want to use mine for ash, so it makes a big difference if it handles fine stuff or not. I might buy one and try it out.

[alan m]

maybe this company is teling the truth. there have to be a few at least
if you buy one please let us know.
i too could do with a seperater for ashs and sut

[phil (admin)]

I suspect a larger radius would make it worse for the fine dust.

There are "sweet spots" for the size/mass of the debris you're separating, and the amount of CFM you're using.  The "sweet spot" will dictate the size and shape of any baffle, and the radius of the separator.

As the debris becomes finer, the baffle's slot width can be reduced.  The slot should be sized to about 1.25 to 1.5x the largest piece of debris you envision separating (with exceptions for extremes).  That is, if you're separating ping pong balls, you don't size your slot for tennis balls.  I sized the slot of my original unit at 1.125" to accommodate typical hand-plane shavings.

Provided one sizes the slot appropriately, you can increase the radius and experience a reduction in resistance introduced by the separator, and reduce short circuiting (where incoming debris immediately moves to the exit port and leaves, without entering rotation).

The unit you linked seems to use a relatively small hose (1-1/4"?).  Upsizing it to 2-1/2" (with the corresponding increase in CFM you might expect if connecting it to a higher-powered shop vac) may result in quite a hit to CFM (lots of resistance, which is proportional to the speed of the airstream squared).  In that case, increasing the R would decrease resistance, and it might even increase the separation rate (by reducing short-circuiting).

With the 1-1/4" hose, it may be right-sized (radius-wise), but not baffle-wise.

The baffle is just way too small, and baffles should never be symmetrical as that one.  It allows the air above the baffle to couple to the air below the baffle too effectively, and spin that bottom air mass.  With the baffle being as small as it is, and being symmetrical, I can imagine running it for long periods would allow scrubbing.

The best way to detect scrubbing is with your ear.  Put your ear to the hose between the separator, and your vac.  Those "tics" you hear are debris sneaking through the separator.  You should hear no "tics."

[alan m]

phil.
im thinking of building a seperater for my vac (festool ct22) and building a boom arm.
from reading that last post (some of which i hadnt read before .
i have a 50 gallon drum (same as i used for my 6 " version.)
if i made the top hat the fulll size of the lid but with a 3/4 "(maybe) slot all around.
would that work and have the lowest resistance and less losses

[phil (admin)]

phil.
im thinking of building a seperater for my vac (festool ct22) and building a boom arm.
from reading that last post (some of which i hadnt read before .
i have a 50 gallon drum (same as i used for my 6 " version.)
if i made the top hat the fulll size of the lid but with a 3/4 "(maybe) slot all around.
would that work and have the lowest resistance and less losses

I never really went to the extreme of a 50-gallon being fed by 1-1/4" hoses (which restrict the CFM).  I think it would work fine, though.

The problem with a 3/4" slot the full circumference of the baffle is the coupling of the air masses above and below the baffle.  As the level approaches the bottom of the baffle, you will see more scrubbing.

[alan m]

sorry i meant with the solid part like normal.
i wrote it a bit funny because i was thinking about tapered slots


if i was doing it it would probably be 50mm inlet and outlet to suit my ct22
i would mostly be using it on my festool portable power tools and my12" disk sander
it would be mostly sanding dust or small saw dust.

im not sure what to do
1. use the 50 gallon drumm . (i have 6 sitting there. one for the 6" seperater and 5 spare). it would mean having the same type drum so if the 6" filled and i needed another rum quick i could swap over. but it would take a year to fill  or more

2. use a small drum but when its full i would have to empty it  straight away. i would also have to find said drum

[phil (admin)]

All I know is I wouldn't want to lift a 50-gallon drum filled with sanding dust.  Chips from a planer wouldn't be that bad, but sanding dust packs a drum much better and the weight would get more than I'd want to lift.

[jalar]

I'm not sure it needs a big baffle.

As I understand it from your explanation here, the baffle is meant to separate the air mass above the baffle from the air mass below. This is to keep stuff from re-entering up through the aperture, and perhaps make it out the exit. I think that is a sound idea.

But there may be a good reason that separation is good in this "short cyclone" too. There is a big aperture instead, so that the air below the separator also moves, perhaps somewhat slower than the air above. And importantly, there is an outer rim to the lid at the same height as the separator (the cyclone is not as big as the lid). This means that dust that has gone below this level is forced out, and is hindered from entering the air stream above that height (perhaps not completely, but anyway). The center vortex is blocked by the disc, which this guy calls "vortex breaker" (rather than baffle), so stuff cannot be lifted in the center either. Since the two air masses move at approximately the same speed, I suspect this reduces the turbulence in the interface between the two air masses (above and below the vortex breaker), and this is a good thing. I think the principle is sound here too.

Different principles, similar end result. Now I'm wondering whether there would be a benefit to using both mechanisms in the same device. Perhaps put a baffle at a distance below the vortex breaker, with the appropriate diameter. I might try this out.

[alan m]

i dont know if it will help but try it and report back.

[phil (admin)]

I'm not sure it needs a big baffle.

Definitely bigger baffles work better than smaller.  I've tested both, there is no comparison, in this case bigger is always better.

As I understand it from your explanation here, the baffle is meant to separate the air mass above the baffle from the air mass below. This is to keep stuff from re-entering up through the aperture, and perhaps make it out the exit. I think that is a sound idea.

It is a little more complicated than that.  Once debris falls below the baffle, we want it to settle and stay settled.  Any reanimation of debris (especially fine dust) gives it a shot at re-entering rotation and being sucked out.  So the baffle decouples the air masses above and below itself, and we try to keep the air below spinning as slowly as possible, relative to the air above the baffle.  This makes it much more difficult for fine dust to be resuspended and exhausted.  It also causes the greatest differential possible along the slot, so the slow-moving air below the baffle literally "snatches" fine dust from the fast air moving above the baffle.

Beyond that, we want the baffle to keep anything that IS resuspended as far from the outlet port as possible.  Close to the outlet port, things get pretty chaotic, with slow-moving areas, rotation changes, etc., allowing fine dust to sneak right into the outlet stream.

But there may be a good reason that separation is good in this "short cyclone" too. There is a big aperture instead, so that the air below the separator also moves, perhaps somewhat slower than the air above. And importantly, there is an outer rim to the lid at the same height as the separator (the cyclone is not as big as the lid). This means that dust that has gone below this level is forced out, and is hindered from entering the air stream above that height (perhaps not completely, but anyway). The center vortex is blocked by the disc, which this guy calls "vortex breaker" (rather than baffle), so stuff cannot be lifted in the center either. Since the two air masses move at approximately the same speed, I suspect this reduces the turbulence in the interface between the two air masses (above and below the vortex breaker), and this is a good thing. I think the principle is sound here too.

Different principles, similar end result. Now I'm wondering whether there would be a benefit to using both mechanisms in the same device. Perhaps put a baffle at a distance below the vortex breaker, with the appropriate diameter. I might try this out.

I've made at least 50 separators, and I've done designs very similar to the Virvelind, it isn't an academic question, I'm speaking from experience.

The reason they have that max fill line painted on their bucket is because they need it.  Above that line, a similar design I was testing passed pretty much everything to my shop vac.  And even below that line, there was plenty of scrubbing going on.

Remember that the Thien separator allows you to fill right to the bottom of the baffle (and a little above, actually).  And you can run it continuously without fear of scrubbing.  Test designs with small baffles scrubbed like mad, you certainly wouldn't want to run them when you are not running tools.

You can go the Virvelind model if you like, just mind that fill line, and turn the unit off as soon as you stop generating dust.

[jalar]

Definitely bigger baffles work better than smaller.  I've tested both, there is no comparison, in this case bigger is always better.

In constructions based on your principle, yes. And as I said, that principle is sound.

It is a little more complicated than that.  Once debris falls below the baffle, we want it to settle and stay settled. 

Agreed, I just didn't write that.

Beyond that, we want the baffle to keep anything that IS resuspended as far from the outlet port as possible.  Close to the outlet port, things get pretty chaotic, with slow-moving areas, rotation changes, etc., allowing fine dust to sneak right into the outlet stream.

Yes, and in the short cyclone, this is achieved by a tangential inlet far from the vortex breaker.

I've made at least 50 separators, and I've done designs very similar to the Virvelind, it isn't an academic question, I'm speaking from experience.

So is this guy. He's not an academic, he's a hands-on inventer.

The reason they have that max fill line painted on their bucket is because they need it.  Above that line, a similar design I was testing passed pretty much everything to my shop vac.  And even below that line, there was plenty of scrubbing going on.

That's because the top part of the container is part of the cyclone. Which is why I was wondering if a baffle at the bottom of that would improve things further. But as you pointed out, there is nothing like an experiment to find out.