Shop Vac Style Thien separator - design questions

[Lael]

Wow! just started looking at ways to reduce bags on a shop vac and stumbled across the thien baffle - it looks great!

I've been looking at:
woodgears.ca/dust_collector/cyclone.html

and

youtube.com/watch?v=avVyCBht8VY

as models for a shop-vac style system. The efficiency claimed by Cosmas B is 99.5% - of course it was a limited test with a small volume of material.

www.youtube.com/watch?v=S7B-2TtKqJc - this guy claims that a increased vertical height in the chamber results in better fines separation, and an increased vertical height seems to be common to all three quite efficient systems.

It seems like both Cosmas and Matthias are getting very high efficiencies with what seems to be a taller separation chamber. Any thoughts on whether Cosmas design with an open 360 degree circumference for the baffle is better than a traditional 1/3rd closed thien baffle?


So... I've looked at a bunch of threads in this discussion forum and there seems to be suggestions scattered all over the place - but there doesn't seem to be one place where anyone has collected all the suggestions about the ratios and characteristics that are needed to make a thien separator the 'most' efficient it can be. Any thoughts on some ratios or principles to follow? - I did find the pdf diagram here: http://woodgears.ca/reader/hector/shopvac.html




I was also looking at reducing fines prior to the filter and thought about water filtration as a 2nd stage - send output from thien through water and then into the shop vac. Here are some ideas other people have implemented:
youtube.com/watch?v=ZLL0Qha5NOk - sending air from exhaust into a bucket with water - bubble out of water to exhaust.

youtube.com/watch?v=FKlbc2BYy9I -'bong vac' - vac head with inlet taped off bucket, pvc pipe going into bottom of bucket, holes in pipe going into bottom of bucket (across bottom), water, flywire on top, aluminium straps to hold it in. white vinegar to stop foaming, spiral lid with slit on top of all that to reduce foaming and bubbles.

youtube.com/watch?v=l17CLdqyuts
3 stage - dust deputy centrifuge, into water bucket, into and through shop vacuum with filter - looks effective.

I'm unsure if I can be bothered to do the frequent (daily?) water changes needed to make this work - though bleach / vinegar would help with that  :) ... so a bag and hepa filter post Thien baffle might be the way I go. I do like the idea and cost of filtering through water. Has anyone tried it?

[Clark Savage Jr]

Since no one else seems to have answered and I think I know why I'll bite the bullet.

I, and I am positive many others have considered water as a filter medium. It is widely used in some specialized larger scale separation units [mainly outdoors] but has a lot of drawbacks and issues for - at least my use. First, keeping the water contained and changing it often, unless you filter the water or have some form of deposition/gravity cleaning device, as it becomes more of a slurry it will become less of an available filter medium. Perhaps other fluids are best used. Then you could use it best by also spraying a fine mist into the air in the chamber to agglomerate the fines and other, but then you have a lot of moisture to deal with in your exhaust/fan/filter which you will really have an issue with if not immediately, soon. So if you change the media, fluid, admixtures to make it more "sticky" to dust, then will you also install a secondary baffle chamber with plates [all refrigerated to lower temps to cause the water vapor to gather and precipitate or some type of electrostatic removal [which could be used by itself too]..........and there are more issues after these.......are you going to raise the humidity with air flowing about water in your shop [will you then purchase a dehumidifier].......

I would suggest that perhaps as a final "after the final filter" air chamber in our use it may be more manageable if vented outside but then again you need to bring air in to allow air out or you will not have an optimal [for what you have] recirculating cleaner, but then the space it will take up and here we go again.......

Liquid/vapor separators are great devices, just on our scale a lot harder to make foolproof, manageable and practical. We are not running vacuum cleaners either that deal with limited dust on a carpet [I know of a few OEMs that have sold them]. That's why I, for one, am attempting to rid the stream of as much as possible before my final filter and let the filter deal with the [hopefully] little that gets through. It's just easier, workable and cheaper in the long run.

However, if you can solve the issues, I may be one of those that will jump onto the train with you. So my only comment after this would be please if you have ideas do experiment, and please let us know how you make out by all means.

[Lael]

Thanks for the reply Clark!

Yeah, I was curious about the humidity aspect of it. The shop vacs for sale where I live are all wet and dry so I think that will be ok. Changing the water all the time... that is more of a commitment. I'll try it and post back once done and tested for a while.

Does anyone have any comments about design ratios and height of the separation zone vs fines reduction or Cosmas' design with a full circular cutout?

[tommitytomtom]

I copied Matthias' 5 gallon bucket version and can attest to the efficiency and portability of the design. Mine is connected to my Ryobi BT3K series table saw and it works great !

[handyrandy]

My design all started after being fed up with how easily my 12 gallon Rigid shop vac clogged up when cleaning my shop up. It is an older model with the inlet in the top (orange) portion, so the bags for the newer ones would not fit.

After lurking here for a while, I decided I would make a Thien baffle for my shop vac. I didn’t want a separate separator al la “dust Deputy” or a separate can with the Thien baffle in it, I don’t have the room. I wanted to make my separator part of the shop vac itself. In essence, a cylinder that goes between the top motor/blower and the bottom bin. I empty out my bin frequently so not too worried about the dust being sucked out of the bottom bin with such a short distance to the bottom.

The design I settled on has a chamber for the shop vac filter with the Thein baffle set into the bottom bin a few inches. Conveniently there is a step down in the bottom to help seal it. I had lots of scrap wood to use, so I only bought a couple of items: the 24” x 48” 1/8” Masonite and threaded rod and nuts, and only spent $10 on the whole thing. The rest is all scrap material or dust collector fittings that I had on hand from a previous router table build. The dust collector fittings would have cost less than $15.

There is a lip on the shop vac bottom that was perfect to use as a seat for a groove in the bottom circle. But the groove I cut in the bottom circle initially with a 1/8” router bit, did not sit right on the bottom because the bottom was slightly out of round. I had to widen the groove after I had the separator built. I thought of not making a top ring and just put the edge of the Masonite into the mating groove in the top, but that proved to be a hassle. So I made a top ring. I used ¾ ACX ply because that is what I had laying around: don’t do that! Too many voids.

The bottom of the shop vac is about 18 3/8” in diameter inside of the handles. This was used for the bottom circle diameter. The groove was 16 ¾” inside diameter. The top ring is also 18 3/8” and about 3” wide. I used scrap hard maple for the uprights about ¾” square placed every 30 degrees. Once the uprights were attached to the top ring and bottom circle, I placed the Masonite inside and screwed to uprights. It bends pretty easily. Luckily (it was not planned), the 48” long Masonite fit perfectly for all but one segment of the circle, 330 degrees. That is where the inlet is placed.

The inlet is simply a 2 ½” dust fitting into a separate piece of Masonite and a ½” plywood backer attached from the outside. The internal tubing is 2 ½” flexible hose to an angled fitting to a 2” 90 degree sweep ABS pipe for separator. Because the shop vac filter is offset, this internal tubing is not an issue. The center exhaust through the bottom ring is another dust fitting that sort of looks like a bellmouth – wishful thinking…. The Thien baffle is ½” Baltic birch.

A double layer of ½” wide weather stripping (what I had in the leftovers box…) was placed on the top ring for a seal to the shop vac top. This allows the existing top’s “clamps” to be used to attach the top to the cylinder top ring. At first, I just was relying on the groove I routed in the bottom ring to seal it to the shop vac bottom. It leaked at one location even when I sealed the voids in the plywood. A ring of the ½” weather stripping on the ledge of the bottom allowed it to seal up perfectly and still caught the groove for stability. All joints were siliconed to seal.

The weight of the cylinder and the grove in the bottom ring allowed me to not have to use any clamps between the bottom and the cylinder. I also like the height of the unit so I don’t have to stoop down to grab the hose or turn on the unit. It’s about 40” high. It works great!!! I still have an old filter in the vac, but little if any dust is reaching the filter so far. Even when I sucked up dust from my bin under my table saw, very little dust seems to make its way into the filter chamber. I am thrilled with the results!! Note that I have a "muffler" on the shop vac outlet that cuts noise but does reduce velocity and suction a bit.

Being thoroughly satisfied with my crude separator built mostly from shop scraps, I will make a proper Top Hat for my old Delta dust collector similar to Retired2’s design. I might even paint this one..........