J. Phil Thien's Projects

I want to build a tophat separator to sit on a Brute trashcan.  I plan to attach a ring to the outside of the separator sleeve to rest on the rim of the can and for strength I'd like to place the baffle inside the sleeve at the same height as the outer ring & secure with screws through all.  Is there any downside to positioning the baffle up inside the sleeve a few inches?  I think this would be a lot easier than trying to size & place the baffle at an exact spot (touching) inside a tapered trashcan.

Just to clarify--Do you mean "drop the baffle" so it's down inside the drum, putting the slot close to the drum side?

If the DC air is choked off the vacuum created could suck the water out--if the manometer is built to measure static pressure Less than your DC static pressure.

You should be able to find a manometer intended for filter monitoring easily enough.  I found dozens of Dwyer manometers on eBay.

Fascinating ideas and observations Dave.  I hadn't given much thought to how debris gets through the slot.  I guess I just assumed it swirled down like any horizontal-flow separator and eventually finds its way through... and then is trapped (the real advantage to the baffle).  IF your vortex idea is true that means there is a definite mechanism in play forcing the dust down.

I do think you may be correct that smoothing the chamber cross-section to resemble a donut with one square corner at the slot location could increase the efficiency of the "axial vortex" and increase downforce on the dust stream.  Such a shape would then resemble a pump volute in cross section (just more proof that everything useful in physics has already been done).  The one remaining "dead zone" would then be the only area of low pressure that would attract the debris out of suspension--and right into the slot.
I would also wonder if the addition of a bellmouth would allow the air entering the fan to have "more reach" and would support this vortex better than the ragged turbulent flow into a simple straight inlet.

Fairing the chamber and the fan inlet could be a mighty one-two punch that promotes quick debris removal from the air stream.  Maybe.

Quote from: Schreck on March 06, 2013, 02:49:14 PM
My suggestion to insert a straightener and measure the change in amps was directed at guy48065 or anyone with a close-coupled top hat and DC  that are oriented with the same rotation (I didn't think you were tuned in to this thread any longer!)

Sorry--even though I have the test equipment necessary in the end any testing of my system will only be relevant to me unless I do a bunch of changes and test the relative merits.  I'm not motivated to do that any more than retired2 is motivated to try his straws on a normal-rotation separator (by building one).  What he is calling being argumentative was me imploring ANYONE ELSE to post their results with an air straightener.  Evidently nobody else believes in the idea enough to try it.

In a 2-stage DC where the fan sits on top of a chamber (drum, bag or Thien top hat) the air in the chamber should be spinning in the same direction as the fan rotation.  IMO any use of vanes or straws at the fan inlet causes frictional losses greater than any gain you might get from achieving a straight laminar flow.  The distance is too short.  Am I wrong in thinking this?

The issue is completely moot in a system where the separator is remote from the fan.

Older vermiculite is known to come from a source that contains asbestos.  And like asbestos it's not really a problem unless you disturb it...but I want it gone just the same.  Darn stuff keeps filtering down into the kitchen since the ceiling is paneling & not well sealed.

And I've found a hose suggestion as I was looking up other stuff online.  RV sewer hose.   It's 3", spiral-wire but way tougher than dryer hose, and cheap.  Should cost about $25 for 40-50'.

I'm planning to build a purpose-built DC using a 12.5" 3-stage blower (300cfm@15"wc) that's been gathering dust under my bench + a top hat style baffle for the blower to sit on.  This is for use in sucking up vermiculite that's in the attic of my 60 year old log cottage.  What's missing is about 40 feet of flex hose that I don't want to spend much money on :)
3" dryer hose might work on this one-time task but it's so flexible it might be aggravating to use (kinks, collapsing, rips from dragging over obstacles).

Any suggestions where to look for 2.5"-3" budget flex hose in bulk?

My canister-type floor vac has a bypass that opens when the filter bag gets full or the hose is blocked.  It has a little reed in it that makes a harmonica sound when air goes through it.  Something like that would be good to add to a vacuum relief to alert you.  A squeaky from a dog toy perhaps?   :)

The article snips do seem contradictory.  I've read the whole document and believe the section I quoted refers to the impeller inlet while the paragraph retired2 quoted is about the housing inlet.

Quote from: retired2 on February 14, 2013, 08:57:56 PM
You can dismiss what I say, but to disregard what industry experts are saying makes no sense. 

I am NOT dismissing what you have written (or quoted), I'm just trying to get a better understanding.  In your posts you have expressed concern that your counter-rotating top hat may be hurting performance.  As I have said the straightener may have helped you--but is it a universal improvement?
You incorporated this straightener in your counter-rotating top hat and wrote about it 1 1/2 years ago.  Surely someone has tried this on a normal-rotating system to see if it is an improvement?

As for the DOE link...well...
On page 13 "Airflow Control Devices":

Quote
Flow control devices
include inlet dampers on the box, inlet vanes at the
inlet to the fan, and outlet dampers at the outlet of
the fan. Inlet box dampers are usually parallel
blade dampers. Inlet vanes adjust fan output in two
principal ways: by creating a swirl in the airflow
that affects the way in which the air hits the fan
blades, or by throttling the air altogether, which
restricts the amount of air entering the fan. The
inlet vanes and dampers must be designed for
proper fan rotation and are to be installed in such
a way that these inlet vanes and dampers open in
the same direction as the fan rotation. The prerotation
or swirl of the air helps reduce the brake
horsepower of the fan. If the inlet dampers on the
inlet box are located too far away from the inlet of
the fan, the effect of pre-rotation may be lost or
reduced, and horsepower savings may be negligible.

They seem to be saying that the swirl at the centrifugal fan hub lessens the load on the motor.  They go on to state that a reverse rotation increases motor load as it "unwinds" the airstream.  Is it reasonable to assume that zero spin falls in the middle between helping and hurting the fan rotation?

ahh...simple fix:
https://www1.eere.energy.gov/manufacturing/tech_deployment/pdfs/fan_sourcebook.pdf

Dead link.

The thing that's nagging me about the straws is a hunch that in retired2's situation it's a band-aid that improves the undesirable counter-rotation of his tophat. 
"Cavitation" was mentioned.  If anything it seems to me that introducing an air mass to the spinning impeller in a straight line would cause shear--or cavitation.  I have no doubt this did improve performance and noise vs. presenting the impeller with an air mass spinning in the wrong direction.  Has anyone else tried this trick--on a separator that spins the air the same direction as the fan?

Quote from: retired2 on February 14, 2013, 12:14:50 PMMy straws are about 1-1/4" in diameter.  To see photos, look for my build.  It has scrolled to about page 10 now.

To save anyone else the aggravation of searching back 18 months with no useful Search tools:
http://www.jpthien.com/smf/index.php?topic=563.0

OK so your Straightener is a bundle of "straws" similar to what I've seen the Mythbusters use in trying to get decent laminar flow from their cobbled wind tunnel.