J. Phil Thien's Projects

You could have a baffle made of two thin pieces of masonite.  One would be fixed at the typical slot width.  The second would be a circle, attached to the first  at only one point, but slightly off center so that as it was rotated, it would make the slot more narrow.  The resulting slot would not be uniform in width, but that may not matter. 

Quote from: retired2 on February 06, 2014, 08:29:32 PM

So, what my data may be showing is that with a bell-mouth outlet the flange placement can be lower than the generally accepted practice for positioning the outlet pipe.  A lower position might give a single-high unit a slightly higher separating efficiency, and at the same time provide a slight improvement in air flow. 

Sorry to the OP for high-jacking your thread.

This is something that I have thought might be significant, but I can't recall it being discussed explicitly ( bell mouth distance from baffle should be different than a plain pipe end).  In ported loudspeaker designs that use round ducts, the box resonance is tuned by adjusting the length of the duct so it resonates at a desired frequency.  The duct length that achieves the desired resonance is slightly less than the calculated "ideal" length due to end effects associated with the plain pipe end of the duct.  This indicates that the effective length of the plain pipe is longer than the physical length. 

The end effects associated with a plain outlet pipe may behave in the same way, so the distance between the effective end of the pipe and the baffle is shorter than the distance from the baffle to the end of the pipe that we measure.  When fitted with a bell mouth, the pipe is extended and a structure is provided to guide the air into the outlet with less turbulence.  So I would expect the ideal distance from the baffle to the bell mouth to be shorter than with a plain pipe.  Most of the design guidance has been given assuming a plain pipe.

In one of the bell mouth threads there was a link to a paper that had great images of the fluid dynamics of a plain pipe vs. a bell mouth.   It's worth looking at the images on the second page of the linked PDF and comparing the end of the physical pipe or bell mouth with the velocity flow profiles.
http://www.jpthien.com/smf/index.php?topic=550.msg4477#msg4477

Quote from: mxc106 on February 06, 2014, 01:37:23 PM

Before this I hadn't seen a setup where the air was "pulled" through the whole system.  Are there fundamental reasons for that, or are the reasons simply that it's difficult to implement in practice for some of the reasons stated?

Implementation issues aside, what do we gain by filtering air before it enters the blower?  The separator will have removed ~95% of the wood waste before the filter, so only fines would be removed by the filter.  What impact do fines have on the capacity of the system?

The enclosure around the filter will add some pressure drop that you would not have in a typical system; I would bet this is a larger negative than the positive from having no fines enter the blower. 

So who has seen tests on blower capacity with and without sawdust and without fines?

Quote from: mxc106 on February 05, 2014, 01:53:49 PM
I recently saw an article and accompanying youtube video from John Heisz at ibuildit.ca (I can't post the external link, but I'm sure you can find it) where he adds a Thien baffle to the dust collector ring as many have done before, but he still uses the filter bag, and the impeller is "after" this setup pulling air through the system.

Thoughts?

This arrangement encases the filter in a wood cabinet that will be under negative pressure;  it will probably experience more air leaks than the standard arrangement having the filter downstream from the blower.  This will reduce the system CFM at your tools, so any benefit that might exist would probably be lost.  Requires more material. Hides the filter, making cleaning more difficult, less likely to occur....

Quote from: flagelpater on January 23, 2014, 09:23:12 PM
I guess I should maintain the same distance off the baffle?

That is a good question and I don't recall it being discussed: if you add a bell mouth, should you maintain the same distance from the baffle that you would have with a plain pipe?  Retired2 may have experimented with this on his build. 

If the blower impeller spins at 1800 RPM and the air entering the blower inlet is also spinning at 1800 RPM and in the same direction, then the blower would move no air.  If the air is spinning at 900 RPM the blower will move some air, but not as much as when the air entering the blower is not spinning at all.  Air entering the blower that is spinning in the direction opposite that of the impeller is bad, as you would expect.

Adding a straightener will introduce some pressure drop, but it is far less significant than the benefit from increasing fan output.

Try searching Google Images for "inlet guide vane" and you will see many examples of devices that manipulate the pre-rotation of air entering fans.

Thaiscience.info seems to be overloaded at the moment   :(

There was a thread regarding CW vs. CCW last year that covered this issue.

Quote from: hankh on October 04, 2013, 09:57:40 AM
...except removing the seal - still not sure what that refers to...

I think Alan is referring to the rubber gasket inside the hub of the inlet.  This would cause unwanted turbulence.

As far as I can tell, the purpose of the cones is to make sure the dust falls into the center of the bag  ;D

The cone does add strength to the ring, so complete removal is probably not a good thing. Consider swapping the two rings and installing them upside down.  This would place the inlet below the cone and allow a baffle to be installed.  If the cone extends up too far past the ring, it may need to be trimmed in order to fit the Wynn filters. 

Here is my 2-bag Grizzly from the 1980's; my plan is to flip it upside down.

Quote from: alan m on June 21, 2013, 12:17:01 PM
everything looks good except for the right hand side of the inlet. cut that back flush with the outside of the seperater.

like this:

Quote from: LoneShark on April 13, 2013, 02:38:35 PM
...My question is Static Pressure Loss for these two mods ----- has anyone measured the before and after??  Im just curious as Im about to re-plumb the shop, and we must be mindful of SP losses throughout the system otherwise its a lot of wasted effort (and money) if not done correctly.

In reading many posts I'm not finding and true measured results ( I may have missed it - if so please point me to the proper post ).  If you have measured the SP Loss on these and would like to share the results I'd love to see them.

I have been reading the forum posts and find the most interesting threads are those where the relative performance of different system designs and configurations are discussed.  retired2 has a great thread on the Delta 50-760, which integrates the blower and the filter "ring" into one housing.  Dust collectors with a blower separate from the filter ring are probably more common, however.  The blower and filter ring can be re-arranged and therefore offer a number of possibilities to incorporate a separator and optimize airflow. 

Since I will soon be moving my shop into the basement, I am about to build a top hat that can be installed either before or after the blower.  Through work, I have access to test equipment (pitot tube, manometer, kW and SPL meters), so I intend to measure a few combinations and post the results.

Some of the configurations on my list are stock single stage DC, same with baffle, top hat before stock single stage DC, same with baffle in DC ring, top hat after blower.  There are many other tweaks that could be measured, but first I intend to look at the major component arrangements.  I am open to suggestions....

Quote from: BernardNaish on March 27, 2013, 04:06:19 PM
Hi, In the unlikely even that the DC actually draws 16 amps .....

The motor label is a statement of what the amperage would be at a given voltage if the motor is connected to a 1.5 HP load at steady operation.  The actual motor loading depends on the blower and everything connected to it: the filters, the hoses, ducts, fittings, blast gates etc. 

Upon start-up, the amperage will exceed the nameplate amps for a few seconds, but quickly settle down.  Here is a record of the amps drawn by a 1.5 HP dust collector, sampled at 1 second intervals.  It is served by a 20 amp 120 volt circuit breaker.  The (imported) motor nameplate does not list an amperage, but I would expect it to be 15 - 16 amps.  Starting amps were 3x this, but only for a second or two.

Quote from: jojonz on April 08, 2013, 02:22:55 PM
The inlet is definitely below the cone, and the bottom of the cone would be 5" from the top of the Thien baffle when built.
Another pic with it up the right way.

Forget what I said above.  Your ring and cone are similar to many current dust collectors on the market.  I see no reason to remove the cone.

Here is a picture of an old-style ring and cone:

That is an old-style DC ring with the inlet above the cone.   I have a 1984 vintage Grizzly with a similar cone & ring.  Leaving the cone in place, at the bottom of the ring, will force the dust to the center, which is opposite what we want.  We want dust at the outside of the ring and air in the center. 

Your other option is to flip the ring upside-down, install a baffle below and a chimney above in the hole of the cone.  Making it a dome...with an oculus.
You may need a plywood ceiling to cover the hole in the cone and support the chimney.  If you are also planning to install a pleated filter, this ceiling could be made larger to facilitate attaching the filter. 

Flipping the ring changes the alignment with the blower, however.  If you plan on keeping both on the mobile base this might be an issue. 

Good analysis of the 50-760 application. 
I think one of the reasons the 50-760 was reviewed so well is that it eliminates the flex hose 90° connection between the blower and the filter "ring". 

I think you could retrofit the 50-760 with the following approach:
1. a 3/4" thick ceiling with outlet/chimney.
2. attached to the side of the ceiling, hang a ring of galvanized steel or plastic laminate (Formica, e.g.) perhaps 8" tall.  This would need to be trimmed to permit the blower discharge to enter the ring without turbulence.
3. attach a thin Thien baffle to the laminate ring, perhaps 1 or 2" above the bottom of the ring.  Unsupported portion of the baffle to be hung from the ceiling using a thin threaded rod

The whole assembly could be dropped in from above.  How you support it depends on whether you are using a bag or a cartridge filter.  The cartridge filter approach might be easier because you could extend the ceiling to support the filter as well as the ring and outlet. 

Here is another paper that includes fan curves showing the impact on airflow, static pressure and HP on systems with pre-rotation in different directions.  See figure 2c.  The fan curves confirm what retired2 found when he installed straighteners to correct his counter pre-rotation. HP and therefore motor amps fell, airflow did not change drastically, but fan efficiency was greatly increased.  So a decrease in amps does not always mean less airflow, it could mean higher efficiency.

http://www.krugerfan.com/brochure/publications/Tbn010.pdf