CW or CCW?

[Schreck]

Well, I am very new to the forum, and I haven't read all of the threads.  But I did read your "5" rectangular inlet..." thread and found it very illuminating.  Measuring velocity pressure was a good move when you found the amp readings to be so close together.  I am curious about your test process: what did you use for an anemometer, was there a single reading taken in the center of the duct and was it fixed at the same location so it could not move in between tests?

[retired2]

Well, I am very new to the forum, and I haven't read all of the threads.  But I did read your "5" rectangular inlet..." thread and found it very illuminating.  Measuring velocity pressure was a good move when you found the amp readings to be so close together.  I am curious about your test process: what did you use for an anemometer, was there a single reading taken in the center of the duct and was it fixed at the same location so it could not move in between tests?

I purchased a new Kestrel anemometer on ebay.  I forget the model number.  Kestrel is the same brand Phil uses, and I followed his practice for taking readings, i.e. take one reading at the edge of the pipe and one in the center, then average the results.

You have to be careful with these devices because very few can handle the velocities of small bore dust collection systems.  My readings were just inside the allowable range because I have a 5" system and I took my measurements some distance from the fan.   

If you are measuring velocities that you think exceed the limits of the anemometer, simply use a reducer, in this case an increaser, to up the pipe size where you will be taking your measurements.  Then just do the math to convert the fpm's for the larger pipe size to the smaller size.  And of course fpm can easily be converted to cfm for any given pipe size.

On about page seven of the thread for my build there are some photos of my test setup for anemometer readings.

[guy48065]

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.

[Schreck]

Evidently nobody else believes in the idea enough to try it.

Or maybe they are testing as we write and simply haven't posted yet!

[alan m]

i think the reason that it isnt on here more is that most people that build a seperater are happy with it the way they have it. they may mean to improve it but cant get around to doing it.
im like that. i built my 4" very crude seperater  really fast 
then built my 6" version quickly (slow to post it thow)
but am slow to get started on my 8" version. i cut the  some of the pieces but cant get the time to do it yet.
it is down to the fact that my 6" version is working well. i could leave it there its that good
most move on to other jobs and shop improvments that are a higher priority

i added an 8" flex hose between the 8" dc inlet and the 6" seperater
it was 6" before . i think there is more suctionbut its hard to tell. when thats a smooth pipe with the air straightener it should improve again

[gunrackguy]

retired2 I was following your build and noticed you have the same DC that I have with a CW rotation, and you separator has a CCW rotation and/or spin, so I guess that is the way to go or do you need to add strengtheners as this discussion implies. I am just about ready to build something similar to what you have and am undecided as to the direction of the separator. I like the idea of providing a new base for the entire unit. I have the pleated cartridge filter on mine.

[alan m]

if you put an air straightener inbetween it shouldnt matter which rotation the seperater is spining
build it what ever way works best for your shop

[retired2]

retired2 I was following your build and noticed you have the same DC that I have with a CW rotation, and you separator has a CCW rotation and/or spin, so I guess that is the way to go or do you need to add strengtheners as this discussion implies. I am just about ready to build something similar to what you have and am undecided as to the direction of the separator. I like the idea of providing a new base for the entire unit. I have the pleated cartridge filter on mine.

I built a CCW separator because it was what gave me the best piping configuration, and also the best access to the separator and plastic waste bag.  As I eventually concluded, a close-coupled configuration should have an air straightener regardless of rotation.  If an air straightener is used, it makes no difference which rotation you choose, both should perform equally.  So, do what I did, use the rotation that suits you approach piping best, but be sure to use an air straightener.

Building a new base for the 50-760 has a lot of benefits.  As anyone who owns one knows, the support legs and brace seem to interfere with everything you want to do.  When I built my new base, I built it slightly larger than the Delta base, and the four legs do not sit in a rectangular configuration.  One leg is pushed back further to provide a clear straight run for the incoming main.

[retired2]

i added an 8" flex hose between the 8" dc inlet and the 6" seperater
it was 6" before . i think there is more suctionbut its hard to tell. when thats a smooth pipe with the air straightener it should improve again

Beware the placebo effect!

[Schreck]

  If an air straightener is used, it makes no difference which rotation you choose, both should perform equally.  So, do what I did, use the rotation that suits you approach piping best, but be sure to use an air straightener.

Here is an interesting paper that seems to confirm this.  Look at test case #4 on page 9.  The diagram indicates the rotation in the cyclone outlet is opposite that of the cyclone.  With straighteners, it does not matter.
http://www.banksengineering.com/Fan%20Troubleshooting%20ED100.pdf

[alan m]

i added an 8" flex hose between the 8" dc inlet and the 6" seperater
it was 6" before . i think there is more suctionbut its hard to tell. when thats a smooth pipe with the air straightener it should improve again

Beware the placebo effect!

iv noticed that since i changed the hose there is less noise . i had to tape a piece of timber to the 6" hose to stop it osilating from the suction. the 8"cant move like that because it is a lot more ridgit. and there is no obstruction there.

there does feel to be an increase in air flow at the end of the duct run but it is only small .
i also havnt tested it  so it could be a placebo effect

[retired2]

  If an air straightener is used, it makes no difference which rotation you choose, both should perform equally.  So, do what I did, use the rotation that suits you approach piping best, but be sure to use an air straightener.

Here is an interesting paper that seems to confirm this.  Look at test case #4 on page 9.  The diagram indicates the rotation in the cyclone outlet is opposite that of the cyclone.  With straighteners, it does not matter.
http://www.banksengineering.com/Fan%20Troubleshooting%20ED100.pdf

Or look at Case Study #2 on page 7 - it also confirms that an air straightener will improve performance of a system where there is pre-rotation, regardless of direction.   

Good find Schreck, another really good resource.  Too bad the ductwork and fittings suppliers like Oneida Air Systems don't sell air straighteners for the common sizes of round duct.  I've got a small sheet metal break, so I will fabricate my own once it becomes a priority.  In the meantime, the plastic tubes are working just fine.   

[Schreck]

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

[retired2]

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

Another good find Schreck.  It is probably worth repeating that installing an air straightener where pre-rotation exists can result in a lower amp reading while still producing more air flow.  Those two statements seem contradictory, and anyone who has read the thread on my build will see that initially I thought the air straightener was decreasing fan performance because I was looking at amp readings, which were going down.  Only when I took anemometer readings did I realize the air straightener was giving me the best of both worlds, i.e. more air and less power.