Bell mouth outlet pipe?

[Vodkaman]

The hot oil method works and was my first thought. I make fishing lures and we use this method for shaping polycarbonate. I have never tried it with anything this big though, but definately works.

I would probably make a male former and lay up some fibreglass, with some wood ribs laid in, to add some stiffness to the shape. The trick is making the former, but it is not that difficult.

Great links, I love seeing mans inginuity at work. This is what we do.

Dave

[retired2]

I would probably make a male former and lay up some fibreglass, with some wood ribs laid in, to add some stiffness to the shape. The trick is making the former, but it is not that difficult.

Dave

Dave,

I've never worked with fiberglass, but if I am envisioning the male former correctly, it sounds like something that could be turned on a lathe pretty easily. 

[Vodkaman]

Yes, but I do not have the luxury of a lathe. If you have the capability to turn such large blocks, you could turn a bell mouth, but it would be cheaper to buy one I guess.

Fibreglass is very easy to work with and done right, would offer a good, strong solution. Lots of Googling first, to get the feel for the process.

Dave

[retired2]

Yes, but I do not have the luxury of a lathe. If you have the capability to turn such large blocks, you could turn a bell mouth, but it would be cheaper to buy one I guess.

Dave

Well, the price was right so I picked up a 5" bell mouth this week at a local shop.  I decided to post a few photos of it now because my separator project is on hold until I recover from a bad back - old age problems! 

In the first photo, you can see that the heigth is only 2-5/8", so there is not much of a neck to work with.  That can easily be corrected by attaching a length of straight pipe similar to the one in the second photo, but shorter.

The third photo shows the diameter of the bell is 9".  It remains to be seen what will happen when a flange that large is installed in the separation chamber.  The benefits of the more efficient air entry could easily be lost if that large flare upsets the dynamics of the air flow in the chamber.

I'm going to start building my separator with the premise that a bell mouth exit port does not require any changes to the established configuration for a top hat design.  I will experiment with the depth of penetration of the bell mouth into the separation chamber, although I'm not sure how I will know if one position is better than the other unless there are dramatic differences.  I might even try straight pipe to establish a base condition, but again I don't have a clue how to measure it for comparison purposes. 

[phil (admin)]

If you have an ammeter, you could measure the current draw of the motor.  If it is pulling more amps with the bell mouth, then it is moving more air.  I'm not sure if the differences would show up in current draw, but worth a check...

Or, an inexpensive weather-vane anemometer may also work the trick.

[Don_Z]

Are you intending to install this inside your separator as the exit pipe? As I believe that the science behind the bell mouth would cause enough of a disturbance inside the vortex that the separator. I am planning on using a few of these as well on my current Thien Scroll Inlet project, only my attachments will be at the machine locations and the actual impeller itself. Keep us posted on how this works out for you. My project is two phased. One is a standard "Top Hat" Thien seperator. The second, is using a Scroll Inlet method to test on which theory will yield the most benefit. The Scroll is a rather unsightly looking beast sitting on top of the trash can but I am borrowing its science of increasing air velocity while maximizing the interior separation stability and efficiency of the vortex.

[retired2]

Are you intending to install this inside your separator as the exit pipe?

Yes, my plan is to start out placing the bell mouth in the separation chamber in about the same position as I would a straight pipe.  Then I'll experiment with higher and lower positions to see if anything changes.  Of course, if I move it all the way to the top, then it becomes an exit port much like what you plan to put on each of your pieces of equipment.  That would seem like the logical place to start, but I am assuming Phil has already tested straight pipe in that position, and if it didn't work for straight pipe, I doubt it will work for a bell mouth.

I don't think there is any question that the bell mouth is the best port configuration for the machinery end of the DC system.  There you are trying to suck up maximum air and dirt.  In the separator, you are trying to suck up maximum air, while leaving the dirt behind.

It is not out of the question that the inefficiency of a straight mouth pipe is the very reason the Thien separator works.  Wouldn't that be a gas! (pun intended) 

[retired2]

If you have an ammeter, you could measure the current draw of the motor.  If it is pulling more amps with the bell mouth, then it is moving more air.  I'm not sure if the differences would show up in current draw, but worth a check...

Or, an inexpensive weather-vane anemometer may also work the trick.

Phil, 

My bellmouth separator is not quite ready for testing, but I thought I would run some tests on my existing system to see if an ammeter can detect differences in performance.  I started with extreme conditions figuring if the ammeter couldn't differentiate between those, it had no chance of detecting differences in separator setups. 

All readings below are out two decimal places because that is what my ammeter is capable of (whether it's that accurate or not is another story).  Also, readings bounce around about +/- 0.03 amps during any test, so the numbers below are an average. 

Deadheaded 15.29  (no blast gates open)
Wide Open    16.90  (only a 5 ft. hose attached to DC inlet)
Bandsaw       15.95  (my longest equipment run)
Sander          15.76  (long run with two smaller dust ports)
Floorsweep   16.29  (short run and 5" port)
Jointer           16.19  (medium distance with large port)
Planer            16.35  (shortest distance with large hood)

The only point to all these numbers is that it shows the ammeter is detecting differences in loads for each situation, and the numbers differ in the direction expected, i.e. the smallest load moves the most air and therefore draws more amps.  Conversely, the biggest load (deadheaded) moves the least air and draws the fewest amps.

So, will the ammeter detect differences in separator setup conditions?  Since there is only a 1.6 amp difference between the extreme conditions above, I am skeptical.  However, I intend to give it a try.

I don't own an anemometer, so I can't do any wind speed testing.  I'll check ebay and Craigs list to see if I can find one really cheap.  It looks like new ones start at about $25 and go to three digits.

     

[AndyF]

I wish Parts-Express had a brick-and-mortar store near by.  I'd love to see how 4" dust collection pipe would connect to a 4" flared subwoofer port:
  http://www.parts-express.com/pe/showdetl.cfm?Partnumber=260-403

Not bad for ~$3.


Andy

[retired2]

I wish Parts-Express had a brick-and-mortar store near by.  I'd love to see how 4" dust collection pipe would connect to a 4" flared subwoofer port:
  http://www.parts-express.com/pe/showdetl.cfm?Partnumber=260-403

Not bad for ~$3.


Andy

Great find Andy.  I read some of the reviews on that website and one of them said it mates up to PVC drain pipe. 

At $3 I'd buy it and ask questions later!

[Pillguy]

I really thought this article in the first post was great! It really showed that some systems cannot support 6" ducting and the bell mouth fitting idea is excellent.
I am in the process of building my 1.0 DC system with a delta 760-50 with 4" pipe and will be trying some of these flares to optimize my system.
:)

[retired2]

I really thought this article in the first post was great! It really showed that some systems cannot support 6" ducting and the bell mouth fitting idea is excellent.
I am in the process of building my 1.0 DC system with a delta 760-50 with 4" pipe and will be trying some of these flares to optimize my system.
:)

I purchased my 50-760 largely on the basis of that review.  Here is another excellent article that became my bible as I was building my DC system.

http://americanwoodworker.com/blogs/shop/archive/2010/10/25/central-dust-collection.aspx

[plauale]

Retired, looks great. I have experience with anemometers and would not vouch for cheap wind or sailing versions for ductwork measurements. I suggest building a simple orifice plate with water manometer readout (coffee is easier to see). Plus it will cost you nothing but time.

http://en.wikipedia.org/wiki/Orifice_plate

[retired2]

Retired, looks great. I have experience with anemometers and would not vouch for cheap wind or sailing versions for ductwork measurements. I suggest building a simple orifice plate with water manometer readout (coffee is easier to see). Plus it will cost you nothing but time.

http://en.wikipedia.org/wiki/Orifice_plate

Thanks for the heads up.  Since my previous post I started checking the specs on some of the "affordable" anemometers.  I discovered that their maximum measurement is about half the velocity of a wide open DC, so at best they would provide an inaccurate reading, and at worst would self-destruct.   

[phil (admin)]

Retired, looks great. I have experience with anemometers and would not vouch for cheap wind or sailing versions for ductwork measurements. I suggest building a simple orifice plate with water manometer readout (coffee is easier to see). Plus it will cost you nothing but time.

http://en.wikipedia.org/wiki/Orifice_plate

Thanks for the heads up.  Since my previous post I started checking the specs on some of the "affordable" anemometers.  I discovered that their maximum measurement is about half the velocity of a wide open DC, so at best they would provide an inaccurate reading, and at worst would self-destruct.   

I use a Kestrel.  I often up-size the pipe to the next size (so 2-1/2" gets adapted to a length of 4", a 4" would get adapted to a length of 6", etc.).  I take my measurements at the end of the up-sized pipe.  The Kestrel can handle something nuts like 7800-fpm.  But switching to a larger section of pipe makes other tests I perform easier, too.