CV1800 - What's wrong?

C

craigclick

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​ I'm very happy with the system I installed a couple of years ago. Although it's my first system and I've nothing to compare it to, when we're humping we'll fill 10-15 208ltr bags a day.

My problem is with sanding dust. We recently bought a sanding calibrator and are two weeks into using the heck out of it. But a lot of the fines are being blown into the shop underneath my clean-out box and the upper back where there are some gaps between the cabinet and the wall.

We cleaned the filters before using the sanding machine. We do this by disconnecting them, taking them outside and knocking them against the ground and finally blowing compressed air through the pleats. Since then, you can see by the photos what's happening. Perhaps it's always happened, but hasn't been noticeable until now. We've always had the occasional problem of keeping the cyclone clean to allow the light sensor to pass.

When we turn on the blower there is always a huge puff of fines that come out of the vents below the cleanout box. There are no fines in the cleanout box. The door that encloses the bag section shuts against doorseal.

What am I doing wrong?

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I would recommend that you check your dust collection bin and its connections and any penetrations that may be allowing slight leakage. Any infiltration will impact the settling of all solids into the bin because of air coming back up from the bin into the base of the cone. That (even slight) airflow will cause the finest dust to be re-entrained into the exhaust air moving up into the blower and out to the filter bank. Use a smoke stick or a lit cigarette to trace all of the seams and penetrations in the bin for leaks and seal them with silicone sealant.

Hope this helps.
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We call it a 'calibrador' here in Mexico; it can be either a belt sander or drum sander that 'calibrates' solid wood panels or dressed lumber to an exact overall thickness.

McRabbet - the bin area is tight. I did use a smoke source to test. So what - it has to be in the connections above - right? I thought I had sealed it well when assembling. I would have to dis-assemble and re-assemble the entire unit - two days - which would be difficult in scheduling.

Could it be the hole with the grommet next to the intake that is supposed to balance the "dead space"? Perhaps some dust build-up on the inclined piece inside that is affecting the airflow? I suggest this as there is an occluded section next to the grommet on this inclined piece of acrylic that is inside the cyclone. It's hard to see through the exterior whether it's only a small layer of dust that built up from static action, or indeed there is a bunch on the inclined piece itself. I hope this making sense. Thanks for your input.
 
Craigclick,
The hole with the grommet is under negative pressure so dust should not leak out there. More likely the leak is from the positive pressure area from the blower housing down through the filter stack including the cleanout at the bottom of the filters. Since you see dust at the mount I suspect the blower housing.
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Craigclick,

We cannot see the pictures that you posted in your opening post, so I can only suggest other possible sources for the fine dust bypass you are observing. Please try to post pictures as *.jpg or *.png images. If possible, show us the configuration of ductwork as it enters the cyclone -- if there are any bends within 4 - 8 feet, the incoming dust-laden air may be very turbulent which will greatly decrease the efficiency of separation down the spiral inlet ramp and into the cyclone. Your symptoms indicate incomplete separation of dust within the negative pressure sections of the system -- very little dust should be getting to the positive pressure side (from the blower outlet through the filters). But you have also stated that you are removing 10-15 208 Liter bags of bin dust daily and even at 99.99% removal efficiency, you will get some fine dust bypassing the filters (I'm guessing about 0.4 Liters using your numbers). I would recapture that bypassed dust with an additional small collection duct where your most serious leakage occurs and recycle it back for reprocessing through the cyclone. At least you would be capturing it at "the source", rather than having it discharge into your woodshop space. Just my two cents worth.
 
The flex hose before the cyclone is worse than the bends. If at all possible you should replace it with a rigid ducting.

I don't know if you have a leak inside the sound enclosure or if the dust around the bottom gets stirred up after changing the bag. I think you need to do a really really good cleaning of the inside of the enclosure so there is no dust anywhere in it even to the extent of removing the insulation temporarily, possibly replacing it later. With it cleaned out you'll be able to see where it may be leaking from after a number of short runs, checking between.

With the filters up against the fibreglass/mineral wool you are blocking the airflow out of them to some extent.

The exit port of the presumably filtered air back into the shop is too small adding to the back pressure. The area should be 2 to 3 times bigger than the area into the cyclone.

You mentioned taking the filters outside and cleaning them. If you are not close to other buildings or people, exhausting outside or moving the entire DC out there will make it safer for you and your workers. Something to consider later if it is allowed.

Pete
 
Thanks for all of the comments; I'll work on all of them, with the exception of moving the DC outside, which is not possible. Also, the flex hose before the intake is only 18" long;do you think that's an issue?
 
What I do notice now, after the dust has settled inside the cyclone, is that there is a buildup of fine dust on the inlet ramp, from the grommet all the way to the top, several inches thick.
 
Craigclick,

Several aspects of your configuration are causing the problems you are having. 1) The inlet ductwork with both flexible duct and elbows within the last 6-10 feet are causing turbulence and decrease the efficiency of separation in the inlet ramp and upper section of the cyclone; 2) Your bin sensor will never detect a full bin situation until the entire box below it (your bin) is entirely filled. The sensor relies on the lowest portion of the inlet to be blocked for about 8-10 seconds before tripping the alarm -- with the bin inlet allowing free-fall of dust to the bag, the bin inlet cannot ever fill until the bag has completely overflowed and the entire box gets filled; 3) The dust bin box as configured will not be tightly sealed during operation even though it is under negative pressure. If your picture is typical when the bin door is open, dust will contaminate the gaskets around the door will make it very hard to seal. Any leakage will produce re-entrained dust in the main cyclone and dust-laden air will pass through the blower into the filters as you are finding. Once the filters get a dust cake on their surface, your entire extraction system efficiency drops significantly; 4) as already pointed out, the return air port is much too restrictive and will cause back pressure.

Solutions: 1) Replace the inlet side duct with a straight duct section; 2) Cut the bin inlet duct off flush with the inside of the box and use a large heavy plastic bin (like those made by Rubbermaid under the Brute brand name) with a gasket on its upper surface (and perhaps a dolly with casters under it) that will make tight contact with the underside of the plywood top of the bin. While the bags you are using may be convenient given the number of bin changes you make daily, the plastic drum will have larger capacity and if on a dolly, will be easy to maneuver (it may be prudent to have two such barrels so the cyclone down-time is reduced). Be certain that you procure a heavy wall plastic bin -- I have seen common garbage bins collapse due to the strong suction of the cyclone. One benefit of this new configuration is that your bin sensor should work -- just be certain that the optical path between the two sensors is cleaned off. I would recommend that you also thoroughly clean off the cyclone, blower and closet interior so you can monitor if you continue to have dust accumulation there -- they should stay clean if the configuration is correct.

Hope this helps.
 
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