J. Phil Thien's Projects

That seems counter-intuitive to me.  If the air entering the fan  spins in the same direction as the fan shouldn't there be less turbulence?  What is an air straightener?  If it's just a pipe then the air is de-coupled from the dirty air spinning around in the chamber, but is still spinning--inside the pipe--because it's coupled to the impeller.  Unless it's one of those bundles of plastic straws I've seen used to straighten a fan output.  In which case when used on the inlet I would think there would be some sort of shear effect going on where the "straightened" air hits the spinning impeller.  That can't be good for CFM or noise.

It's hard to wrap my mind around these effects.  I didn't have any fluid dynamics classes in college.

In any event many of these options aren't easily available to me.  My system is in a small closet and the pipes drop in from ceiling height straight down into the lid of my 2-stage DC.  Not much "wiggle room" there to change flow directions or greatly increase DC inlet height.

I'm also confused whether that quote is referring to the system inlet (where I thought spin was desirable) or fan inlet (and how would you control that?).
And in context is that quote about dust collectors where you are trying to separate material from air or ventilation? 

I have a question about "tweaks" or "optimization".  Phil has written that the baffle is itself a compromise intended to work well in most situations.  What little things can be changed to improve performance?  Shorter slot?  Narrower slot?  Tight inlet elbow vs. wide radius vs. maybe an angled straight pipe?

Can any generalizations be made or will it always be "change everything and see what happens"?

Quote from: alan m on February 11, 2013, 11:21:14 AM
retired2 (member here) i think did some reserh into air straighteners. he (?) found benifits in having one

I'd like to read more about it but a search of "air straightener" turned up nothing.


Maybe I'm missing something...Why did Cincinnati Fan use an elbow on the intake of their 2-stage DCs, like everyone else?  Or were they referring to avoiding bends and elbows ahead of the inlet?

It's been stated that inlet angle & swarf flow direction doesn't matter.  I imagine that's true for a separator fed with hoses but what about when the baffle is mounted right on the fan housing?  Seems to me you would want the swirl to run the same direction as the impeller since it's so close it may be "coupled" to the air mass.

OR--is counter-rotation desirable in case it might reduce the amount of fines that get pulled in by the impeller?

Anybody ever play with this choice?

I've gone this far with the testing so I do plan to try the baffle but I need to adapt it a little differently to my drum.

Lid with 12D x 12H shroud removed:


My lid is 24" but the drum is 22" so I made the lipped ring so I could get a consistently good seal.  Just suspending a baffle under the intake scoop will make it a PITA to lift & replace the lid so I will make an integrated ring-sleeve-baffle hanging down into the drum.  Kind of like an internal "tophat".  Alternately I could make a normal tophat and not lose any drum capacity.  I think I have enough height above the DC motor for this and still have adequate lift space for the rope & pulleys.

Are there any other "enhancements" that I should consider for this type of unit?  I've seen mention of bellmouths, woks and chimneys on the impeller intake--would that make any difference used with the baffle?  Maybe some sort of guard or vane so the impeller doesn't "see" the intake scoop?

So at, say, less than 1/2 full the baffle has no benefit?  Good to know so I won't waste a bunch of time testing it on 1/3 drum of dust :)

Answer is good--but pretty subjective.  I have a 45 gal. white translucent barrel like you've previously described.  With a backlight I can see the dust swirl.  Presently with no baffle the stream appears to corkscrew down 1 full turn in the drum before hitting the bottom.  I probably can't see the finest flour this way so it may be spinning around endlessly in there but in a test I performed Tuesday night only 1.4 out of 28 lbs of dust got into the bag (no baffle).  That works out to 5% bypass--is that good or bad per everyone's experience?  This test seemed pretty extreme as I normally don't suck up 28 pounds in 10 minutes, and never get more than a handful in the bag per drum-full, and nothing on the walls around the DC.

I'm a newbie to baffle concepts but definitely not new to home shop DC's.  My 2-stage 4" pvc system pre-dates the internet and works fine, despite all the grave warnings about dust explosions that were tossed about in the magazines back then :) 
Although I get very little fines in my bag (less than 5%), and none on the walls of the closet it's located in, I'd still like to try to improve performance.  I'm baffled (ha!) by posts I've read about the desired effect in the drum.  Some posts talk about wanting a dead drum where chips just fall down while other posts talk about spinning the chips out in a vortex.

Which is the intended effect of a Thien baffle?