Cyclone issues - shavings won't drop?

[Cyrus Brewster 7]

I have nearly completed the duct installation for my new CV. I fired it up at the end of the day yesterday to see it run:D. I noticed that the PVC shavings that were in the pipes would not fall out of the the cyclone body. Thinking the lightness in weight was an issue, I put a 1/4" think cutoff piece of handrail in the system - to my surprise it kept spinning around.

My next thought was a leaky trashcan. Today I filled the trashcan with water and witnessed no leaks (I had sealed it ridiculously). My next check was the seal for the lid - it is sealed with 1" wide weather stripping. First check was place the can upside down on my assembly table to make sure the top (lip) was flat - good there. I then put another 1/4" weather strip around the rim to take up any deviations in the trashcan lip.

I put the can back in place. (Before doing this I put a handful of the PVS shavings in the can.) To do this I have to lift the lid a bit, compressing the 6" hose so the initial seal is good to begin with. I then turned the CV on and watched the trashcan and lid get sucked together. Looking through the window in the trashcan I noticed the PVC shavings swirling around - none went back up into the cyclone body. I then sucked up the same 1/4" piece of handrail, and it again did not drop in the can.:confused:

Am I missing something? I am wondering if the hose connecting the cyclone body to the lid is too short causing the swirling in the can (it is the piece supplied by Clearvue). But I do not think this explains why the handrail piece will not drop in the can. The only explanation I have is a leak somewhere.

I am going out now to investigate a little further. Any suggestions would be greatly appreciated. Below are two photos for reference.

260961260962

[Bob Wingard]

Just a wild guess, but, if the debris is being lifted and swirled about AFTER it has settled in the bin, it sounds like the bin is leaking at the bottom. Is there any chance the suction is pulling on the can so hard that it is opening up a seam or a crack somewhere ??? I have a CV with a fibre drum, and have never seen this type of action in my system.

Can you install a trash bag in the bin with a simple tension/weight device to hold it in place ??? I've seen people make such a device out of a length of roll fencing or a strip of light plastic or sheet metal. It just has to be strong enough to keep the bag in the bin, and to keep it from collapsing. For temporary use, even a rolled up piece of heavy cardboard should work.

With the system running, you can also try using an ear plug in one ear, and place a length of rubber fuel line in the other ... then move the open end of the fuel line all around the drum ... you will hear ANY leaks that might be present with pinpoint accuracy.

[Prashun Patel]

Pvc shavings? Could be static electricity if you are ure it is not a leak.

[Phil Thien]

I think Bob may be right, you may have a sneaky leak.

Try this: Get a plastic garbage bag large enough to hold your entire can. Put the can in the bag, attach the can to the cyclone, and now wrap the top of the bag around the bottom of the cone and tape it there with electrical tape with enough wraps to prevent leaks.

Now try it again.

[Cyrus Brewster 7]

Pvc shavings? Could be static electricity if you are ure it is not a leak.

No, I just used the PVC shavings for visibility. I also saw this with a little sawdust.

[Cyrus Brewster 7]

I think Bob may be right, you may have a sneaky leak.

Try this: Get a plastic garbage bag large enough to hold your entire can. Put the can in the bag, attach the can to the cyclone, and now wrap the top of the bag around the bottom of the cone and tape it there with electrical tape with enough wraps to prevent leaks.

Now try it again.

Yeah, a sneaky leak is what I suspected - but no leaks with 31 gallons of water.

I am going to try the plastic bag now.

[Cyrus Brewster 7]

Plastic bag proved the can is airtight. The bag stayed completely neutral when the cyclone was turned back on - same results though. The hose connection appears fine but I am redoing it.

I used construction ply for the lid - lots of voids, splits, etc. I have a suspicion it may be that. Since it is already made (wish I used MDF) I am going to skim coat the underside with silicone. I am hoping to have better results tomorrow.

[Dick Mahany]

Sounds like the CV would make an interesting observational chamber for the study of golf ball flow dynamics. Wish I could offer some help, but this one is a stumper big time.

[Alan Bienlein]

Here is a shot of my dust bin connected to my cyclone. Depending on how many blast gates I have open will determine how much the dust swirls around in the dust bin.

http://www.youtube.com/watch?v=ufolmCfvDXI

[Phil Thien]

Plastic bag proved the can is airtight. The bag stayed completely neutral when the cyclone was turned back on - same results though. The hose connection appears fine but I am redoing it.

I used construction ply for the lid - lots of voids, splits, etc. I have a suspicion it may be that. Since it is already made (wish I used MDF) I am going to skim coat the underside with silicone. I am hoping to have better results tomorrow.

Was the bag not large enough to attach to the cyclone cone, above the hose? That would have told you if you had a leak in your lid.

[Ken Fitzgerald]

The cyclonic action works by slowing down and reversing the direction of the air within the cyclone funnel. In doing so, the air reduces its particle carrying capability. Gravity works on the larger particles and they fall to bottom and into the can. The smaller dust particles remain trapped in the slower moving air, go through the blower and into filter.

The shavings should fall due to gravity. If they aren't falling, you have a leak between the top of the can and cyclone.

I would us wood shavings rather than PVC shavings. PVC can be affected by static electricity and could be suspended.

[Cyrus Brewster 7]

Was the bag not large enough to attach to the cyclone cone, above the hose? That would have told you if you had a leak in your lid.

Well Phil, I only isolated the can. The bag, indeed, would not have fit over the lid onto the cyclone body. However, it did tell me that the can was not the problem. I am actually glad I isolated it and narrowed it down to either the lid or connecting hose, although the hose really was not the problem (I think). As of now (as I stated earlier) I have coated the entire underside of the lid with silicone and will be redoing the weather stripping - my fingers are crossed for tomorrow.

As for the weather stripping, I picked up the black 1 1/4" stuff at HD.

[Cyrus Brewster 7]

jThe cyclonic action works by slowing down and reversing the direction of the air within the cyclone funnel. In doing so, the air reduces its particle carrying capability. Gravity works on the larger particles and they fall to bottom and into the can. The smaller dust particles remain trapped in the moving air go through the blower and into filter.

The shavings should fall due to gravity. If they aren't falling, you have leak between the top of the can and cyclone.

I would us wood shavings rather than PVC shavings. PVC can be affected by static electricity and could be suspended.

Ken,

After I posted I put a 4" piece of cable tie into the system. It made it down to the last 8" of the cyclone body, at which point it kept bobbing up and down - definitely air coming up.

[Phil Thien]

Well Phil, I only isolated the can. The bag, indeed, would not have fit over the lid onto the cyclone body. However, it did tell me that the can was not the problem. I am actually glad I isolated it and narrowed it down to either the lid or connecting hose, although the hose really was not the problem (I think). As of now (as I stated earlier) I have coated the entire underside of the lid with silicone and will be redoing the weather stripping - my fingers are crossed for tomorrow.

As for the weather stripping, I picked up the black 1 1/4" stuff at HD.

1 1/4? Is that 1x1/4 or 1-1/4 by something?

If the silicone doesn't fix it, next time you put the lid on the can, give it several wraps of 2" wide masking tape around the rim of the lid, and the can, to make sure it is sealed there. That way you can eliminate the weather stripping as a possible culprit.

[Michael W. Clark]

Are you saying the cutoff is suspended in the cone or in the trash can?

[Cyrus Brewster 7]

Are you saying the cutoff is suspended in the cone or in the trash can?

Suspended in the cone.

[ian maybury]

Can't say for definite as my connection hose is quite long (about 15in), and my cone is steel, so who knows what goes on in there.

There have been occasional reports about that a very short connection (although yours looks much like what CV recommend) can lead to problems. It does seem the drum is a functional part of the cyclone - some of the air rotation continues down into the drum, and the debris drops out when it expands into the drum.

Another possibility is that some report that dust can appear to be hung up in the cone/hose even though it's actually working through. As though there can be a sort of residence zone can form that delays the passage of the dust. My hose does this, i thought for a while that it wasn't working but it in fact seems to be just fine.

There's others about with more experience.....

ian

[Cyrus Brewster 7]

Ian,

I could live with just some dust swirling around, but it seems that a small piece of cutoff should drop.

As per Phil's advice I taped around the junction of the lid and bin (it has a weather stripping gasket). I also taped the outside of all of the seams on the bin for good measure. The inside of the lid has been coated with silicone and I put rubber splicing tape on both sides of the connection hose to ensure a good seal. I have not had any improvements.

The only information I forgot to add was that I opted for the 16" blower and hosing from CV. I wonder if the extra suction has something to do with it, although I do not think it does.

Quite frustrated now but I will stop worrying about and finish the duct work. I may just buy a fiber drum from McMaster and see what happens.

In the video the two pieces do not drop until I turn off the blower.


http://www.youtube.com/watch?v=atgPMq45jPk&feature=youtu.be

[Michael W. Clark]

Suspended in the cone.

I would suggest one of two possibilities: 1) you have a leak as others have suggested. Use tape to cover the joints and isolate the problem. 2) the cone diameter is small compared to the size of particle you are trying to pass through it, so it stays suspended due to the clean vortex coming back up the middle of the discharge.

Particles are captured by moving them to the wall of the cone. As the spinning air and particles enter the drum below, the particles fall out, the vortex breaks, and the clean air goes back up through the middle of the cyclone. High efficiency cyclones use a separate dust reciever/vortex breaker to perform this function, the the dust is stored below in a separate bin or conveyed away. When the dust bin is directly below the cone (absent a vortex breaker), there is a lot of funky stuff happening at the cone discharge and in the top of the dust bin. This is why you can only fill your dust bin to certain level before you get carry over. If you have a longer hose to the top of the dust bin, it helps, but it can get abraided fairly quickly.

Mike

[Michael W. Clark]

Just saw your video. Too much flow can be a problem too, but didn't CV design the cyclone for the flow? Try varying the flow by opening/closing the gates to see if you get the peices to drop. Do small pieces (dust) go out like they should?

[Cyrus Brewster 7]

Just saw your video. Too much flow can be a problem too, but didn't CV design the cyclone for the flow? Try varying the flow by opening/closing the gates to see if you get the peices to drop. Do small pieces (dust) go out like they should?

The model I have - CV1800 - was designed for their 15" impeller. I opted to up it to their 16" impeller that comes with the CV-MAX - this is designed for 8" mains. I am running all 6" (plan to upgrade in the next couple of years with a bigger shop) so the flow should be cut down quite a bit.

Anyway, I sucked up another piece of poplar and it drop when I closed the gate half way. The swirling in the bin also dropped dramatically with all gates closed. I did a bunch of cuts on the bandsaw (the only hookup finished) and it appeared (?) to work OK. I may put a gauge after the blower now to measure how fast the filters plug up before doing any other cutting.

Thanks for the tip.

[ian maybury]

Just wondering Cyrus. You mention 'finish the duct work'. It seemed like the drop at which you put the test pieces in was open and very close to the cyclone.

It is normal as above (at least judging by my set up) to get a a fair amount of swirling around of dust, and i know from the noise made that larger pieces can spin around in the cyclone (but they seem to run against the walls) for a few moments (or quite a lot longer) before they drop. My duct runs are in 160mm spiral, and the shortest (purely as a result of the shop layout) is of the order of 40ft from the cyclone. They in addition pull through lengths of flex hose, and through machine hoods. My fan runs on a VFD at 55Hz (about 3,150rpm) rather than 60Hz to reduce the noise a bit too. The result must be that there's a lot more resistance and less flow than would be the case if it was running at 3,450rpm through an open drop and a very short run of smooth duct to the cyclone.

As Michael said cyclones are designed for a specific air flow, and there may be a possibility of problems when it gets too high - although i've never heard of an issue with a CV. It seems the step up to the larger rectangular section in the CV inlet chute is there to ease the entry to the cyclone by matching the square section of the ramp and also to drop the velocity a bit. There's also a view that a good long (say 7ft) straight run into the cyclone improves it performance by smoothing the flow, although many seem to be run with bends close in - but maybe in lower air flow/higher resistance scenarios.

Wonder though if it's possible that in your test situation that you're getting more air flow than the cyclone likes? Before you do anything maybe try throttling the flow as he suggests by part closing a blast gate by progressively increasing amounts. It would be a good trial - if the behaviour changes significantly as the flow reduces it might well suggest there is an upper limit. Bearing in mind that is that a reduced flow must eventually (?) result in stuff dropping through anyway.

This may be a red herring - in that so far as i remember (?) the 16in CV impeller is designed to run more than one machine at a time if necessary - it seems likely therefore that the cyclone should be well proven on on higher airflows. It'd be worth asking CV what they think.

It'd be good to hear some input from others running these systems in that as before there is a tendency for dust to swirl around quite a lot before dropping which can be misleading - i can't remember specifics, but one or two definitely mentioned having as a result been worried when they first ran theirs....

ian

[David Kumm]

There will be lots of swirling in a small diameter cyclone. Mine is similar in that I run a 7.5 hp in a 20" Torit but a piece of wood will bang against the cyclone forever before finally dropping out. When you go to 8" mains you may get worse as the cfm can exceed what the cyclone is designed for. Just will men separation won't be quite as good. Dave

[ian maybury]

Here's a few links to the CV forum - the second i think from Ed Morgano who was the original owner of CV. It's pretty clear from them that quite a degree of dust swirl is normal - even when there are no leaks. Seems like maybe there's a degree of recirculation that goes on - that dust that doesn't drop into the drum gets picked up in the upwards centre flow, only to get thrown out to the wall again and again before dropping through. It gets worse/the turbulence becomes problematical with leaks. It's worth noting too from the last that dropping the flow below a certain level stops the spin but also stops the cyclone working...

The acid test logically enough is whether or not you are getting any carryover into the filters or the dust tray.

ian

[Alan Bienlein]

Cyrus if you look at the video I posted of mine you will see the dust in the dust bin start to swirl as I open a blast gate. It gets progressively worse as more blast gates are opened but settles right back down when I shut them. I have the 16" impeller from clearview but I built a 20" diameter cyclone and I sometimes experience pieces of wood swirling around in the cone until I shut the cyclone off or enough saw dust goes thru to knock the piece down into the collection drum.

[Cyrus Brewster 7]

Cyrus if you look at the video I posted of mine you will see the dust in the dust bin start to swirl as I open a blast gate. It gets progressively worse as more blast gates are opened but settles right back down when I shut them. I have the 16" impeller from clearview but I built a 20" diameter cyclone and I sometimes experience pieces of wood swirling around in the cone until I shut the cyclone off or enough saw dust goes thru to knock the piece down into the collection drum.

Hey Alan, I tried to reply to your post last night, but for some reason was having problems. I tried some different scenarios with the gates open at different degrees. I am fairly confident that I do not have any leaks now. Thanks for this - it pretty much describes what is going on. I checked the clean out after dumping some saw dust in and doing quite a bit of cutting on the bandsaw - nothing. Hopefully it is not in the filters. I will blow them out tomorrow to find out.

[Cyrus Brewster 7]

Ian... The first drop where you see me put the pieces in was closed after doing so. The air flow was coming from an opening about 35' away. However, you are correct in your assumption of my short run into my cyclone. It is less than 3'. I knew going in this was not optimal but am now starting to reconsider this. Going to around 7' of straight intake will add 6 - 8' to the total length of all runs - not a big deal as this was the reason I went with the 16" impeller.

I am debating on doing this now or waiting to see what happens. The set up is such because of existing cabinets. As I write this, though, I think I know what I will do and I think it will be worth it.

[ian maybury]

We only know what we see on our own set ups Cyrus, so this is just conjecture - but it does seem that there's plenty of recirculation that goes on in the hose/bottom of the cone when the cyclone is working right. So that it may not be obvious if (and this may or may not happen) the flow can get so high on some installations that it transitions to some different flow pattern that causes less effective separation.

I'd for this reason be slow to tear too much apart or form too firm a view that there is a problem until you run it for long enough to properly check whether or not you are getting significant amounts of dust and chip carry over into the filters. i.e. into the drop out drawer at the bottom of your filter stack. Maybe talked to CV too.

Conjecture, but judging by the fluid flow patterns that arise in other devices it's possible that if a high flow problem of this sort can arise that any such transition could happen pretty suddenly. i.e. that dropping the flow just a bit could change it.

Also conjecture, but several of us have seen that larger pieces of material like blocks of wood can take a while to work through. We instinctively feel they should immediately drop because they are 'heavy', but it's possible that the extra area they present makes it easier for them to stay in suspension. If only because the low(er) speed circulating boundary layer attached to the surface of the cone and the hose than captures dust and chips and 'spirals' them down the wall is likely very thin. i.e. a block may because of its size struggle to avoid projecting out enough to get caught in the upwards flow in the centre as it nears the bottom.

It's hard to say for definite whether or not a long straight inlet will have a big effect given that so many seem to be running without them, but it's unlikely to do harm.

Keep on posting, i'm dead interested to hear how this shakes out...

ian

[Tony Rodoracio]

Cyrus,

I have been running a CV for a couple of years now and it has always done what you describe. The larger offcuts will spin for awhile but eventually drop. The regular dust spins and drops out rather quickly.

[Prashun Patel]

Mine has been doing it for a while but i notice it does not effect efficacy.

[John Lifer]

The problem is not with a leak, I really don't think you will find one. The problem is the design of the cone vs the flow. As others have hinted at, you have too high a flow to drop out the particles. From my view, the cone is too long in relation to the diameter. If the velocity of the air remains too high at the wall of the cone, the chips will not fall out of suspension. The larger the diameter, the slower the velocity of the air and the chips would slide on down as gravity would be larger component than the axial rotation.... I note you cut flow and things started dropping. Until filter loads up, you might have to do this.

[Bob Wingard]

If you want to be certain that there' no leak in the chip bin ... take it out. Put a small (6") disc made of non-porous material on the bottom of the cyclone ... tape it up thoroughly to keep it in place and to seal any leaks. Turn the system on, and try the same pieces that won't fall out of suspension now. If they go right to the bottom of the cyclone, you have a barrel leak ... if they still stay in suspension, it may be "normal" for your system.

[Michael Dunn]

Has anyone seen the CV video demo where the guy sucks up a 25' tape measure into the cyclone? I'm pretty sure it was a CVC. The tape measure dropped immediately. I know some have followed my cyclone install. Mine is sheet metal so I can't see what's happening. All I know is that there is a ton of chips in my steel trash can beneath my cyclone. I kind of wish I could see it. 1. Because that would just be awesome and cool. 2. So I could know if mine is doing the same thing.

I'm so tempted to try the tape measure trick. It shouldn't damage anything, right? Maybe I'll use my 16' Fast Cap tape.

I'm certainly no expert here, but those pieces you fed into the system were quite small. I can't imagine that the force of gravity is stronger than the air movement in the cyclone. Try something heavier. I can't imagine small wood chips or even large wood chips from a planer would be able to just drop while the air is still moving.

My $.02.

[Michael W. Clark]

If the cyclone is working with dust, I would let it run. These peices you are putting in are very large with respect to the cone discharge diameter. In addition, they are also very light. It is easy for them to get caught up in all the air currents at the bottom of the cone, especially with no other loading. You will have swirling in your barrel, the vortex continues past the cone, the particulate drops out (slung to the outside of the barrel) and the clean air goes back up the middle. This is important, becaue if you fill your barrel to the top, you will get re-entrained material pushed into the filters, especially the small stuff.

Mike

[Cyrus Brewster 7]

If you want to be certain that there' no leak in the chip bin ... take it out. Put a small (6") disc made of non-porous material on the bottom of the cyclone ... tape it up thoroughly to keep it in place and to seal any leaks. Turn the system on, and try the same pieces that won't fall out of suspension now. If they go right to the bottom of the cyclone, you have a barrel leak ... if they still stay in suspension, it may be "normal" for your system.

I just tried this with the sane results - so no leaks in the bin. Thanks.

edit: not pun intended with sane but...

[Cyrus Brewster 7]

I'd for this reason be slow to tear too much apart or form too firm a view that there is a problem until you run it for long enough to properly check whether or not you are getting significant amounts of dust and chip carry over into the filters. i.e. into the drop out drawer at the bottom of your filter stack. Maybe talked to CV too.

ian

When I woke up I thought the same thing before I read this. To extend the intake would require moving a cabinet that would encroach on the only place I can store a full sheet of ply (20' x 20' shop). I am going to let the system run, get results and go from there.

Funny how when one gets involved, knee deep, in a project, that the thoughts (or frustrations) involved sleep right next to you. My wife will be happy when it is all done.

[Michael W. Clark]

When I woke up I thought the same thing before I read this. To extend the intake would require moving a cabinet that would encroach on the only place I can store a full sheet of ply (20' x 20' shop). I am going to let the system run, get results and go from there.

Funny how when one gets involved, knee deep, in a project, that the thoughts (or frustrations) involved sleep right next to you. My wife will be happy when it is all done.

Straight on the inlet is helpful, but the main thing is that you do not put a horizontal elbow counter-current to the rotation of the cyclone. Elbows in other directions will have much less of an impact (if any) on the efficiency.

Mike

[Cyrus Brewster 7]

If the cyclone is working with dust, I would let it run. These peices you are putting in are very large with respect to the cone discharge diameter. In addition, they are also very light. It is easy for them to get caught up in all the air currents at the bottom of the cone, especially with no other loading. You will have swirling in your barrel, the vortex continues past the cone, the particulate drops out (slung to the outside of the barrel) and the clean air goes back up the middle. This is important, becaue if you fill your barrel to the top, you will get re-entrained material pushed into the filters, especially the small stuff.

Mike

Mike... I was getting started on enlarging the hood of my jointer to 6". When I opened the plate I noticed a pile of chips/dust in the dead spot. I scooped them in a container and fed them into the system about 25' from the cyclone. The cyclone worked as I that it should have - a little swirling around (previously stuck by static) until a handful went in. Everything dumped right into the bin.

Everyone else... From the posts that Ian linked from the CV forum and from what I seen posted here (thanks), what I witnessed at first was normal. Because I wanted to check for leaks (even tough I was confident I did not have any), I only sparingly put material into the system (PVC shaving - bad, and a light piece of poplar - bad) so I would not clog the filters on my first go around.

The fact that the Clearvue is, well, clear, is a double edged sword. If I could not see what was going on I would have saved quite a bit of time tinkering around these past two days and would have been able to relax with some BBQ and a cold beer.

As I stated earlier, I will be adding a gauge on the exhaust side of the blower so I can visually see when the filters need to be cleaned. I will also be taking notes on what is going into the system - material being cut (MDF to wood), duration of cutting (as best as I can estimate), gauge results, dust run lengths to each machine, etc. It most certainly will not be anything scientific, but I am hoping to get a "feel" for my system. Maybe I will change a thing or two... or maybe I will finally just get to woodworking and forget about shop setup for a while - it has been going on for almost two years.

[Cyrus Brewster 7]

Straight on the inlet is helpful, but the main thing is that you do not put a horizontal elbow counter-current to the rotation of the cyclone. Elbows in other directions will have much less of an impact (if any) on the efficiency.

Mike

I actually read this somewhere else (made sense) so was not worried with the elbow going down.

[Clay Crocker]

Cyrus,

I think that may be normal. I have a Super Dust Gorilla (metal cone, so you can't see what is going on inside) and every once in a great while my compound miter saw will send a small off cut into the cyclone and I can hear it rattling around inside the cone. Sometimes I have to shut off the cyclone motor to get the offcut to drop into the drum. Clay

[ian maybury]

That sounds like a good move Cyrus. Please report if you can manage it.

One to be cautious about is testing the cyclone with the outlet at the bottom of the cone blanked off. It may function in this situation, but watching and reading about cyclones suggests that the drum pays a significant part in dropping out chips and dust. As in the swirling and downwards moving flow is maintained right down through the hose. The solid material really only drops out when this flow (which carries it) expands into the space at the top of the drum and slows right down. Which explains why they prefer to have a little empty space always left above the chip fill.

I have a long (roughly 15in) clear connecting hose between the cone and the chip drum, and the swirl (or at least the movement of dust and chips in it) is visually obvious right down the full length of it. It all suggests that the spin is pretty intense. Since air 'stuck' to the wall of the hose seems to be moving down into the drum, there presumably must be a balancing flow of air moving back up the centre of the hose and up the centre of the cyclone into the fan inlet tube. Pretty amazing really that it's able to maintain such a structured flow in this situation, and maybe a reflection of just how much energy/velocity gets concentrated up in it.

One thought I've had is whether the corrugations on the flex hose matter or not - or whether a smooth walled (hard to organise - we rely on the flex of the corrugations to lift the top off our chip drums) hose would help. The corrugations might conceivably help 'screw' debris down it's wall if they match the direction of spin of the cyclone, or oppose if not. (as in my own case) They may not matter, in that fast moving air has a way of forming stationary boundary layers that in effect 'fill' surface irregularities (at the expense of reducing the effective diameter of the port or whatever) when it enounters surface roughness.

That the direction of spin of the fan matches the layout of the cyclone is by the way something else to check if it seems to be acting up....

ian