J. Phil Thien's Projects

Wouldn't the bellmouth effectively increase the diameter of the opening, and thereby reduce the measured CFM across it's mouth? If you are measuring air speed, and converting it to CFM by multiplying that by the area of the pipe, what diameter do you use for the bellmouth? The outgoing pipe size, or the outer lip of the bellmouth? 

Also, to me it looks like you have more air straightening material in the pipe than you need, and that may be reducing flow. The article linked to below points to a three vaned deice with a streamlined body at the center of the pipe as being the most efficient design.

http://www.jpthien.com/smf/index.php?topic=1048.0

I used window sealing foam from a big box store to help seal my top hat to a brute trashcan. It works well, but the foam isn't as stiff as I might like, and gets mushed down. I still think it seals ok, but I haven't gotten around to testing it. You can buy stiffer versions of the same self adhering foam from McMaster-Carr, a great website for supplies in general.

The Thien Baffle systems we mostly deal with on this site are best suited for larger dust, which is why most of the systems here end up with the Wynn Environmental filters tomittytomtom refers to. If you built a small Thien style separator and powered it with your Dyson, you might end up with longer intervals between filter cleanings because less of the coarser dust would get caught in the filter. That is assuming there is any coarser dust in what you are vacuuming.

If you were to make a baffle separator for this specific task, I think you could increase your odds of sucess by designing it with a very narrow drop slot.

I commend you for wanting to get that nasty stuff out of your loft, but wonder if carefully stapling down some Tyvek or similar vapor permeable membrane before you put down your flooring might not end up being an easier and effective solution.

Thanks, Mik - a much better answer than ""Would this work?"  Not likely, stick to proven designs."

michaelmew, I agree with your point about the forum needing to encourage experimentation. If you have the money and time, why don't you do a quick and dirty version of your design as an experiment?
Retired 2 is probably right, but you never know. Personally I've lost interest in this forum because it seems like nowadays it could just be replaced with plans of R2's separator, and a note to "do it like this."  And also, I've finished building my sweet version of the Thien tophat and it is working nicely. 

I remember a thread on here a while back on this subject, and the conclusion was that the shape of the bin under the baffle didn't matter a whole lot. You could try searching for that thread.

I had my local sheet metal fabricator make up one for me, and I think it cost about 45-60 dollars. It isn't as heavy-duty as the pieces I bought from Spiral Manufacturing, but it is just fine. The one thing I'd suggest is you try to get all of your pipes and fittings from the same source, so you don't have to spend as much time joining pipes and fittings that are of slightly different sizes. 

You all can mock me if you have already figured this one out, but it has taken me a number of times trying to get a good measurement of something round, like a barrel or trashcan, to come up with it. I would normally lay a tape measure across the top in a number of places, trying to be on the diameter as best as I could, and then average the results. The other night, I was measuring the Brute trashcan I'm building my system around, and was getting diameter measurements that varied by as much as an inch. So I decided to measure the circumference of the can, and then used math to determine the diameter of a circle with that circumference. I haven't built the part that needs to fit the can, but I have high hopes for the accuracy of this method.

Do any of you have any tips like that that you might take for granted, that you wold want to add?

drxlcarfreak, I think most people make the top hats the size of the trash can or other container so that the dust falls directly into the can below. If you made the separator bigger than the can, you'd need to build some sort of funnel or other means to get the dust into the can. There has been some discussion about airflow patterns in the can, and I think the conclusion is that it doesn't matter a whole lot. There should be a thread titled "Square Collection Box" or something along those lines. 

I briefly considered basing my soon to be built system on some cans I've seen at Home Depot, that are about 36" diameter, and about as tall as a Roughneck. I decided not to use them because the top looked like it would be hard to seal to.

Thanks, R2 - I agree about the importance of not increasing the turbulence to keep the sp losses down. And I guess the only way to know for sure would be side by side testing, which I don't have the desire to do...
Thanks again for the reply. 

Kind of surprised no one has even had a strong opinion about this....

I'm sure at the time there were people who thought bellmouths, rectangular inlets, and double height chambers were crazy ideas, too. The great thing about this forum is the spirit of collaborative experimentation, imho.

steamngn, thanks for your reply. And no worries about the delay, I'n not in a huge rush.

I'll be able to use a large radius bend, and even have a section of straight pipe between the bend and the blower inlet, and that is where I intend to put the straightener, with the blower output going through a short straight pipe into one of the big cartridge filters. A whitepaper (Attached) that I probably found in one of R2's great threads is a very through study of air straighteners, hopefully you will find it interesting.

Thanks again!

I have searched the site for information on this, to no avail, so I'll ask the members -

Has anyone done research on whether or not the relative smoothness of the interior of the baffle chamber affects fine dust separation? So many of the top-hats we see are made with clear plastic sides, which are very slick. If you were to use another surface that had some texture, do you think it might create a zone of slower moving air against it, or perhaps some sort of beneficial turbulence that might help with the fine stuff?

An extreme example would be lining the chamber with something like carpet - you could imagine that grabbing a lot of dust, but it would likely add too much resistance to the set-up. I am considering using bending plywood to make the circular part of my top hat; I could leave it as it comes, or cross sand it with coarse paper to make it rougher. I could try to paint it "slick", or even line it with thin sheet metal, to make it behave more like the plastic sides.

So do we have anyone who has tried this sort of thing, or who can model it on a computer, or has a strong intuition, or even just a strong opinion?

Thanks, Dusty

Sorry to bump this old thread, but I wanted to give a performance update on this project.
Having now used this for close to a year, I am more and more happy with it. I have emptied the container now three times, with no noticeable drop in suction that would make me want to change the filter. I'm not sure why it got clogged up so quickly the first time, or hasn't clogged since.