Intake positioning design and clarification

[mrgedman]

Hello! 

This is my first post, I have read the forums considerably, and have not found a specification on intake design.  I have seen intakes with four different styles, and one seems to stand out as superior.  I am curious if it might be the extra 9% I have heard people talking about - "mine gets 90% of particulate, it would be great to get 99%". 

I hope I can be clear in describing the diagrams I threw together in paint.

1 is where the entire baffle system is coated with something, and the hose attaches at the end of the square appendage (where the little x are). 

2 is where the hose or assembly sticks into the appendage somewhat,  but does not approach the circle, and is not cut at all, it is left square (from top view).  Typically only the circle is coated in these diagrams, not the appendage. 

3 is where the hose or adapter sticks into the appendage, approaches the circle, and is trimmed to match the circle.  In this case, the coating material wrapped around the circle is not the length of the circumference of the circle, it is shorter than the circumference by the width of the appendage.  I imagine this leaves strange voids where the x are found. 

4 seems to me to be superior.  It functions in much the same manner as style 1, but it elimanets the problem from switching from a square appendage to a circular hose.  It also functions in a similar manner as style 3, but with the voids surrounding the intake adapter filled in to match the circle.  In 4, A lexan piece would be cut to length of the circumference and would have a very long ellipse cut out to receive the intake hose/adapter

I am not sure if one might want the strange little dead spot (x) or not.  I have seen videos, pictures and descriptions of people using all 4 styles. 

Which is best and why? 

I hope I was clear enough with the picture/thought.  If you guys want, or if I am unclear, I can go through design videos/thread and link them to these 4 styles. 

Thanks,

Ged

[mrgedman]

You may have missed the point of the post.

Which is better? 

Or is the "classic thein" input the best, from the top, with nearly 180 degree bend, but a perfect circle, and likely more strange dead spots from the input... Something makes me think his way is best for shop vacs, and the arm model is best for dust collectors... Perhaps the near 180 degree bend in the pipes near the input reduces some static pressure yet maintains cfm?  Beats me :)

[galerdude]

From what I've read on the forum, I haven't noticed a lot of the Thien Separator builders building more than one of the intake designs you have described. It might be hard to get a comparison of which is better because of all the different systems and their respective individual mods. I'm sure that theory and opinions would be plentiful. I'm also sure in the end, you will wind up building the best system possible taking into account your particular needs. It sounds like you've really done your homework and are ready to start building your Thien Separator. I say, go for it! If you should decide to build various intake designs, run tests and share your findings; I can only imagine that many forum members would be grateful.
Just for reference, my system was designed and built using option '1' in your illustrations.

Respectively,
Gale

[dabullseye]

you need to go back and see if people are using a rectangular. or round pipe coming in. i think the best is to use a rectangular pipe and keep it the same height as the inside of the separator. this really helps smooth out the air flow as it hits the wall and begins it way around the separator.

[mrgedman]

you need to go back and see if people are using a rectangular. or round pipe coming in. i think the best is to use a rectangular pipe and keep it the same height as the inside of the separator. this really helps smooth out the air flow as it hits the wall and begins it way around the separator.

See you are assuming model 1 is best.  I assume that either model 1 or 4 is best, but I do not feel comfortable judging (without testing) that a transition from a circular to a square input is more efficient than maintaining a circular intake... If that is the case, and model 1 is more efficient, what length of square appendage is best?  Are they different for shop vacs and DCs?

I'm sure that theory and opinions would be plentiful.

I can only imagine that most everyone would consider their design superior, but would not be able to cite reasons other than "because I made it and it took considerable time/effort/money"  :)

I'm also sure in the end, you will wind up building the best system possible taking into account your particular needs.It sounds like you've really done your homework and are ready to start building your Thien Separator. I say, go for it!

I sure hope so.  That is the idea behind this post :)

If you should decide to build various intake designs, run tests and share your findings; I can only imagine that many forum members would be grateful.

Ideally, I made this post to see if anyone has experimented with different inputs, and what they found.  If this has been done, I am surprised there is no post on it.  Perhaps I will be the one to do it.  Frankly, if/when I build one, I do not imagine that I will get it functional and then feel the need to mess with it more.  I am just a hobbyist, so I don't really care about squeezing a few extra percent efficiency. 

It would be very difficult to control all the variables in such an experiment.  Perhaps you guys could help a bit with that, or offer suggestions.   

Here are a few important controls and design considerations for the experiment:  I would imagine that any tests would need to require the inside of the shop-vac to be nearly spotlessly clean, and the dust piles would need to have consistent quantities/ratios of fines and chips, as well as consistent mass.   It would need to be sucked up at the same rate, to avoid unfairly overwhelming one design or another, although there could be differences in efficiency based on speed.  Perhaps 1 works better when there is lots of dust flying in fast, for example, but requires those conditions to outperform 4...  Next, and most importantly and most difficult, I would need a way to measure the dust collected on the inside of the shop vac and the filter.    If I had a very precise (laboratory grade) digital scale, that gave grams to 3 or 4 decimal places, perhaps I could weigh the whole thing before and after sucking dust, and report the weight change.  This assumes I have access to a very fancy scale.  Qualitatively looking/shaking the filter may provide a good answer to the question, but only if there is considerable difference, which there likely isn't.  It would also likely take large amounts of dust to create a noticeable difference, adding to the experimental challenge.  Do I test 1 cubic foot of dust, 1 lb of dust, or more?  . 

It seems easy enough to make model 1, and then modify it to be either 2, 3 or 4.  Using one tophat with two different intakes, I would need to design the tophat such that the top could be sealed well, yet still be removable, which seems like a huge challenge. This all seems like an awful lot of work If i want to experiment with the "classic" then input as originally described by Phil (iunput from top of cricle, not side), the mod would be more tricky to make without compromising my original "appendage and circle" design...  If trying the classic input, It would need to be in a tophat and not recessed into the can so that the edges of the baffle are airtight (not relying on the wall of the can to make a perfect fit" to further control variables.  The tophat seems to be far more efficient for this reason.  Again, this conclusion is not based on any empirical testing, but seems to be a consensus among the community. 

Just for reference, my system was designed and built using option '1' in your illustrations.

Gale, I actually know yours was style 1.  In fact, your design was the last one I looked at when I felt the need to address this problem.  Of all the models I looked at, yours seemed to be one of the most efficient, if not the most efficient from the sample I reviewed, but I am curious if the appendage helps or hurts, and under what circumstances.  An area where the intake diameter is considerably increased just before the circular cyclone....Hrmm....

Either 1 or 4 has to be the best designs in my opinion, but I can't tell which just by looking at it.  I would also guess (as I have nudged at) that one design may be better for a DC while the other would be better for a shop-vac.  4 would seem to increase the speed of the vortex, but would likely increase pressure as well, while 1 seems to decrease both speed and pressure somewhat...

After writing this gigantic essay, I think I likely will test differences between 1 and 4, but as I do not have a DC, will be using a shopvac.  I would not be surprised to find they are almost identical,  (small margin of error), but I'd be less even surprised if gains were circumstantial, and based on power source (shopvac/dc).   Any conclusions I make will be limited in application to shopvacs... Sorry fancy DC boys :)  It would be interesting if I found that the appendage model works best, but that it works even better if the appendage is unusually long. 

Any results or experimental preparation will be posted in this thread, but I will likely start a different thread for my build. 

Thanks to the great community, and the all wise Phil (he is kinda like a god on these forums, isnt he? :) ) for sharing such a great concept. 

[Peter]

I made my a top hat separator for my shop vac. It occurred to me that if I didn't make some way to get into the thing, then it would be extremely difficult to remove anything that might obstruct the works. Indeed, after completing the thing, I delighted in demonstrating its effectiveness by sucking up all sorts of garbage--and sure enough, I sucked up some hand plane curls and the like and a plastic bag. (I used it on leaves on the patio, too. That works great.) Needless to say, these large objects either wouldn't drop through the slot or wrapped around the support post inside.

I was glad that I made the top removable.

It isn't difficult at all. Basically, I put the cyclone and baffle in a plywood box where the top and bottom extend beyond the sides. I then used 1/4" threaded rod at each corner to hold the top on, and for the post that holds the baffle from flopping around inside. Lock nuts keep the rods in position on the bottom of the box, utility knobs allow me to quickly open it up to get out stuff that I probably shouldn't be sucking into my separator, but do anyway.

To seal the top to the box, I made a gasket out of some of that white foam packing sheet. Leakage? Not much: When I first turned the thing on, it collapsed the 30-gallon galvanized garbage can I have the top hat resting on.

-----------

As for your dilemma with intake, I imagine there is very little difference between the worst of your four options and the best. My design is most similar to your option 4, except my pipe extends into the drum. The only time I have to clean out the shop vac is when I've clogged the slot (as in the examples above). Otherwise, it apparently separates everything out of the air--well, everything I can detect, at any rate.

However, I find that there is quite a bit of dust piling up around the circular intake pipe, above and below it. I don't have the skills (or didn't then) to fit the vertical cylinder of the drum to the horizontal cylinder of the intake pipe.

I am currently designing a larger top hat, for use with a dust collector (as opposed to the shop vac). This time, I think I will make a metal transition from the round pipe of the system to rectangular intake in the separator. I an not a pneumatic engineer, but my supposition is that such transition should be gradual, rather than abrupt, that the area of the rectangular section should equal or exceed the area of the pipe. This would preclude just flattening a section of duct, as doing so reduces the area significantly.

My understanding of the way this thing works is that we want airborne particles to collide with the sides of the drum, reducing their velocity which causes them to drop out of the air stream, which ultimately winds up in the center of the drum and is evacuated by the fan. Therefore, anything that can be done to concentrate the particulate stream at the extreme diameter of the interior is preferable.

[retired2]

I am currently designing a larger top hat, for use with a dust collector (as opposed to the shop vac). This time, I think I will make a metal transition from the round pipe of the system to rectangular intake in the separator. I an not a pneumatic engineer, but my supposition is that such transition should be gradual, rather than abrupt, that the area of the rectangular section should equal or exceed the area of the pipe. This would preclude just flattening a section of duct, as doing so reduces the area significantly.

Rectangular duct is less efficient than round duct, so HVAC practice is to upsize rectangular duct by about 10%.  That's the number I used for the design of my round to rectangular transition piece.  However, with the transition piece bolted directly to the separator, the rectangular run is so short it probably has very little negative effect.  That said, I would still use the 10% guide and I would definitely not go smaller.   

[mrgedman]

However, I find that there is quite a bit of dust piling up around the circular intake pipe, above and below it. I don't have the skills (or didn't then) to fit the vertical cylinder of the drum to the horizontal cylinder of the intake pipe.

Peter-  It sounds like you have a slightly different intake, which we will call 5. I hope the updated diagram is accurate.

I can't say I am suprised by the strange voids you mention, and the inability for the filter to work on different size material.  I applaud your removable top, but it sounds to me like it does not work to specifications that I would consider acceptable.  If I spend a number of hours and some money or scrap building this thing, I want it to work considerably better than you describe.  Good work, I dont mean to sound like a dick, but... I expect more. 

My understanding of the way this thing works is that we want airborne particles to collide with the sides of the drum, reducing their velocity which causes them to drop out of the air stream

As far as I can tell, and based on the literature I have been exposed to, The entire thing is about a cyclone, and while smashing particles into the vertical sides of the sphere (cyclone) decelerates them considerably, this is a by product of a more general and efficient idea; the heavy particles in the air are forced to the bottom and outside of the cyclone, where they wind up falling due to loss of velocity, which may or may not be caused by them contacting the side walls; in most cases I would imagine particles would not/never impact the side walls.  Again, this is not based on demonstration. 

Rectangular duct is less efficient than round duct, so HVAC practice is to upsize rectangular duct by about 10%.  That's the number I used for the design of my round to rectangular transition piece.  However, with the transition piece bolted directly to the separator, the rectangular run is so short it probably has very little negative effect.  That said, I would still use the 10% guide and I would definitely not go smaller.   

While the last poster had some slightly useful information, I feel like this is much better.  I do imagine that if there is a difference, it is slight.  I am not sure what you mean by a 10% guide.  Say your intake is 6" circular, so you recommend 6.6" rectangular to accommodate the square?  You have a design similar to 1, and are providing the specs relative to the section? I could see this working in almost the same manner as #4, because the fit of circle to square is closer than most other projects (think 4" circular and 6.5" square... or even a larger ratio.  can site if necessary). 

What if we try to increase the rectangular run?  I am imagining a multiphase action of dust- it hits the tube and is sucked based on how it is received... it hits the short (long?) rectangular appendage, where it is scattered about the perimeter, most concentrated towards the edges of the perimeter of the square/rectangle, then it hits the cyclone where it is more (less) efficiently separated?  This makes sense- moving air quickly through a rectangle should push any heavy airborne material to the edge of the square/rectangle so that the air column can more more efficiently towards the center. 

I think we may be getting somewhere.  Peter, thanks for sharing, sorry if I was a little harsh.  Exactly what sizes are your shop vac (hp/gallon), your baffle (height, diameter, intake position and diameter, and outtake position and diameter) and perhaps your receptacle (20/30 gallon?)

I will be using a 5 (peak) HP 16 gallon rigid shopvac, with a 20 gallon can receptacle, planning on the baffle being 3.25" tall (interior, with approx

[retired2]

The 10% upsizing refers to cross-sectional area.  So, calculate the area of the round duct, then add 10% to that number.  That should be the minimum area of the rectangular duct.

For what it is worth, my design is not like #5, it is like #4 except that one end of the red inlet is round and the other end is rectangular with no voids to accumulate waste or cause increased turbulance. 

Frankly, I don't think a shop-vac separator will be influenced very much by any of these variations, and it certainly doesn't warrant the cost of fabricating a round to rectangular transition piece, so you should simply build the one that is easiest to fabricate.   Even with a large DC system separator, modifications to the basic design only produce subtle improvements in performance, and there is a lot of instrumented test data in the thread on my build to back up that opinion. 

[Peter]

Mrgedman, my intake is not really like your number 5 illustration, in that the pipe is tangent to the inner drum, like your number 4. The dust that collects around the pipe is above and below it, not to the sides as you indicate with the small x marks. And it isn't a great collection of dust--probably in the range of a couple tablespoons-worth. Photo attached.

I agree with retired2 that for a shop vac, the design of the intake is not terribly important. I certainly don't worry about the small inefficiencies inside the separator. What's more important to me, is the nearly zero amount of dust that arrives in the shop vac. The photo attached shows the interior of the shop vac after I had used it to fill a 30-gallon metal garbage can with debris. You can see that the small piece of baggie did not find its way through the slot, but wound up in the shop vac. That happened once.

Now, for the dust collection system I'm designing for my shop, I will pay considerably more attention to details in the separator. I will use a rectangular duct that in plan, at least, matches mrgedman's option #4, but which will be full height of the drum. Anyone reading this who has experience that indicates this is a bad idea, please comment. From what I've read, a shop vac has considerably higher air velocity, but handles less volume than a dust collection system. My shop vac/separator configuration will suck up 1/2" hex nuts through 20 feet of 2 1/2" hose. My 2 HP dust collector will move immense piles of sawdust out of my table saw, but won't pick up anything with significant mass. As it should be: a dust collector is not a vacuum cleaner. :)