Cyclone issues - shavings won't drop?

[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.

[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.