I know the rule of placement for a standard outlet in a single height tophat is 1/2 the height of the inlet centered on the inlet. How does this change with;
(1) Using a bellmouth
(2) a double height, or higher top-hat separator?
My inlet is a 6" metal duct that transitions to a 4"x10" rectangle. My outlet is a spun bellmouth that I'm going to have to attach to the outlet pipe, as the bellmouth is only about 4" high anyhow. The circumference will be about 22" as that's the dimension on the fiber-barrel that I have for my collection bucket.
Let me know if you need any additional information.
There is test data in a table in the thread for my build, just below this post. It shows slight air flow differences between positions, but not much. As I recall separation did not change very much. I think there might be a photo in that thread showing the attachment of the bellmouth to a straight section of pipe.
Ordinarily, I would recomment putting your bellmouth flange at or slightly below the bottom of the inlet. However, you have a pretty tall inlet so I don't know if that is reasonable. Is your double high 20" tall? If so, my advice would be ok.
I use the rule that the outlet should be half the height of the inlet up from the baffle. so it doesn't matter if it is a single ,double or triple height.
I havnt seen any that are more than double height so its hard to say if that introduces any issues.
as for the bellmouth I think it is the same but measured to the bottom rim. so half height up from the baffle to the rim of the bellmouth
Quote from: alan m on January 25, 2018, 12:49:20 PM
I use the rule that the outlet should be half the height of the inlet up from the baffle. so it doesn't matter if it is a single ,double or triple height.
I havnt seen any that are more than double height so its hard to say if that introduces any issues.
as for the bellmouth I think it is the same but measured to the bottom rim. so half height up from the baffle to the rim of the bellmouth
I'm not sure where you found the rule you are quoting, but I've never heard it.
not really a hard and fast rule. but it make sense.
as the separator height increases the outlet has to get longer to get the benefit .
so keeping to half the inlet height above the baffle makes sense
Quote from: alan m on January 26, 2018, 08:40:54 AM
not really a hard and fast rule. but it make sense.
as the separator height increases the outlet has to get longer to get the benefit .
so keeping to half the inlet height above the baffle makes sense
It may indeed work just fine, I had just never heard that rule of thumb. It does seem to produce reasonable locations for all but extreme cases. In fact, as my tests show the performance is not terribly sensitive to position. And ironically the best airflow was achieved when the bellmouth was closest to the baffle. It might be that in that position the air flow into the bellmouth was smoothed by the baffle.
i tried using the bell mouth at halfway also lower and higher. i don't have any hard data but from my testing other than just my observation but i ended up not using the bell mouth and with the outlet flush with the bottom of the top. i did my testing with the table saw and the drum sander and watched what made it to the bag. six years later i have never had to empty the bag and there is less than a gallon milk jug of dust in the bag.
i made this crazy thing with a 10" tire inner tube so i could play with setting.its been under the bench for yrs so its kinda dusty
Quote from: dabullseye on January 26, 2018, 05:15:47 PM
i tried using the bell mouth at halfway also lower and higher. i don't have any hard data but from my testing other than just my observation but i ended up not using the bell mouth and with the outlet flush with the bottom of the top. i did my testing with the table saw and the drum sander and watched what made it to the bag. six years later i have never had to empty the bag and there is less than a gallon milk jug of dust in the bag.
i made this crazy thing with a 10" tire inner tube so i could play with setting.its been under the bench for yrs so its kinda dusty
Quote from: dabullseye on January 26, 2018, 05:15:47 PM
i tried using the bell mouth at halfway also lower and higher. i don't have any hard data but from my testing other than just my observation but i ended up not using the bell mouth and with the outlet flush with the bottom of the top. i did my testing with the table saw and the drum sander and watched what made it to the bag. six years later i have never had to empty the bag and there is less than a gallon milk jug of dust in the bag.
i made this crazy thing with a 10" tire inner tube so i could play with setting.its been under the bench for yrs so its kinda dusty
so your outlet doesn't extend into the separator at all.
I tried that years ago and got a lot of bypass.
I don't think any of us are really qualified to 100% claim anything too many variable in our shops. what works for you might not for me.
that's the interesting thing about dust collection.
Quote from: alan m on January 26, 2018, 05:34:42 PM
Quote from: dabullseye on January 26, 2018, 05:15:47 PM
i tried using the bell mouth at halfway also lower and higher. i don't have any hard data but from my testing other than just my observation but i ended up not using the bell mouth and with the outlet flush with the bottom of the top. i did my testing with the table saw and the drum sander and watched what made it to the bag. six years later i have never had to empty the bag and there is less than a gallon milk jug of dust in the bag.
i made this crazy thing with a 10" tire inner tube so i could play with setting.its been under the bench for yrs so its kinda dusty
Quote from: dabullseye on January 26, 2018, 05:15:47 PM
i tried using the bell mouth at halfway also lower and higher. i don't have any hard data but from my testing other than just my observation but i ended up not using the bell mouth and with the outlet flush with the bottom of the top. i did my testing with the table saw and the drum sander and watched what made it to the bag. six years later i have never had to empty the bag and there is less than a gallon milk jug of dust in the bag.
i made this crazy thing with a 10" tire inner tube so i could play with setting.its been under the bench for yrs so its kinda dusty
so your outlet doesn't extend into the separator at all.
I tried that years ago and got a lot of bypass.
I don't think any of us are really qualified to 100% claim anything too many variable in our shops. what works for you might not for me.
that's the interesting thing about dust collection.
It could be the behavior of 2X separators is a little different than 1X. I have never built or tested the former so I have zero data or observations.
Quote from: retired2 on January 25, 2018, 07:14:47 AM
There is test data in a table in the thread for my build, just below this post. It shows slight air flow differences between positions, but not much. As I recall separation did not change very much. I think there might be a photo in that thread showing the attachment of the bellmouth to a straight section of pipe.
Ordinarily, I would recomment putting your bellmouth flange at or slightly below the bottom of the inlet. However, you have a pretty tall inlet so I don't know if that is reasonable. Is your double high 20" tall? If so, my advice would be ok.
I think I may have seen your chart.. I also seem to recall seeing something about putting it below the inlet. That seems to make sense to reduce by-pass.
I have metal that I'll be using for the sidewalls. It's 24" x 36" and I have 2 to make sure I have enough to make the top-hat. I can do up to 24" with this arrangement, and probably will so I don't have to worry about an uneven cut. I have the room as well, so height is not an issue.
I guess I should have mentioned that I'll be using the HF 2 HP collector and increasing the inlet size to 6" to match the ducting. I may do the impeller upgrade later, but I'm going to try it as-is to begin with.
Quote from: retired2 on January 26, 2018, 12:36:36 PM
Quote from: alan m on January 26, 2018, 08:40:54 AM
not really a hard and fast rule. but it make sense.
as the separator height increases the outlet has to get longer to get the benefit .
so keeping to half the inlet height above the baffle makes sense
It may indeed work just fine, I had just never heard that rule of thumb. It does seem to produce reasonable locations for all but extreme cases. In fact, as my tests show the performance is not terribly sensitive to position. And ironically the best airflow was achieved when the bellmouth was closest to the baffle. It might be that in that position the air flow into the bellmouth was smoothed by the baffle.
Interesting points made here, I may try this as wel.l.. I'm contemplating making the outlet pipe long enough to experiment with flow, thank you for discussing this in my thread as it has given me additional food for thought as I proceed with my build.
Thanks all for the feedback and I'll try to keep this thread updated with my progress on the placement.
So I've been working on this and looking around in my shop and have driven myself to another impasse.
I have a Fiber Barrel that I feel will be sufficient enough in capacity for the amount of woodworking I will be doing, however it is rather narrow in circumference. It's only 17.5" in diameter. With this, I've been considering stepping up the diameter of the Thein separator to about 18.75" and using the rings that attach to the barrel lid, to step up in diameter to get to the separator size. The lid is metal and would be cut to act as the baffle.
My other option is a Rubbermaid Roughneck trash can that would allow me a separator diameter of about 20.5". My hesitation on this is that I don't want to implode the plastic trash can. I know it's not likely, but the concern is there, especially if I am careless and forget to open a blast gate before starting the DC system.
Is there a rule of thumb on diameter of the separator to the inlet/outlet sizes? Both will be 6" on mine.
Any help and opinions are greatly appreciated.
Quote from: Alan H on February 07, 2018, 08:30:17 PM
So I've been working on this and looking around in my shop and have driven myself to another impasse.
I have a Fiber Barrel that I feel will be sufficient enough in capacity for the amount of woodworking I will be doing, however it is rather narrow in circumference. It's only 17.5" in diameter. With this, I've been considering stepping up the diameter of the Thein separator to about 18.75" and using the rings that attach to the barrel lid, to step up in diameter to get to the separator size. The lid is metal and would be cut to act as the baffle.
My other option is a Rubbermaid Roughneck trash can that would allow me a separator diameter of about 20.5". My hesitation on this is that I don't want to implode the plastic trash can. I know it's not likely, but the concern is there, especially if I am careless and forget to open a blast gate before starting the DC system.
Is there a rule of thumb on diameter of the separator to the inlet/outlet sizes? Both will be 6" on mine.
Any help and opinions are greatly appreciated.
There are no magical rules about separator diameter that I am aware of. However, if you go too small, then waste by-pass becomes a problem because the outlet pipe is too close to the separator wall. Since you are using 6" inlet and outlet, diameter becomes more critical. I don't remember if you are planning on using a bell-mouth but the makes it much worse because the flange on a 6" is pretty large in diameter.
I'd recommend you go to HD, buy the Rubbermaid Brute. It is cheap, and you will not collapse it unless you hook up a shop vac to it. I have never collapsed mine and I dead-head it for a few seconds every time I use my system because I have an intentional motor shut-off delay built in to mine. So, when I close my blast gate the system continues to run for about 10 seconds. If you have light gage 6" pipe you have as much chance of collapsing it as you do the brute can.
You need to think about your plans for emptying the drum. I have to transfer everything to a 33 gal garbage bag and carry it out of my basement shop. Emptying the drum into a bag can get messy if the drum is too large. Even with my mid-sized Brute I have spillage that must then be broomed over to my floor sweep where if goes back into the vacuum system. It is pretty easy, but it creates a very small amount of dust which I've already collected once.
Thanks for the advice @retired2.
I'll go with the larger Rubbermaid can, but I think I'll only go buy the Brute if the one I have looks like it's going to give me issues.
The dimensions you show in your thread seem to be about the same, so I'll build mine to work on the bigger diameter. BTW, yes I do have a bellmouth.
I have plenty of casters around in the shop, so I'll build a platform that the can will sit on and self center, and then a cam-lift to raise it to the separator housing.
Quote from: Alan H on February 09, 2018, 06:15:28 PM
Thanks for the advice @retired2.
I'll go with the larger Rubbermaid can, but I think I'll only go buy the Brute if the one I have looks like it's going to give me issues.
The dimensions you show in your thread seem to be about the same, so I'll build mine to work on the bigger diameter. BTW, yes I do have a bellmouth.
I have plenty of casters around in the shop, so I'll build a platform that the can will sit on and self center, and then a cam-lift to raise it to the separator housing.
I don't know what your design looks like, or the drum you are planning to use, but if you are going to build it with even a remote possibility of having to change to a different drum, you need to think about how much work will be involved to do that. It might require you to start over.
I have two Rubbermaid drums in my basement, the Brute, and another one that is a few gallons smaller in size. The smaller one is a nice can and I keep a 30 gal trash bag in it and use it for
general waste in the shop. However, I think it might be possible to collapse that one if it were attached to a vacuum system. It has lighter gage walls and lacks the stacking collar that is built into the Brute. If your Rubbermaid is larger than the Brute, it may have stiffeners built in that will keep it from collapsing.
If you think the flange diameter on your 6" bellmouth is so big that it is causing by-pass, don't be afraid to put it on a band saw and cut an inch off all the way around. You will still get nearly all the benefit of the bellmouth. I've posted a chart several times showing different end treatments of pipe and the efficiency of each. The bellmouth is the best of course, but even a crude flat flange on the end of the pipe makes a big improvement over just straight pipe.
I read in retired2's thread that the reason for the air straighteners was to reduce turbulence in the outlet pipe. I plan to do the straighteners and have purchased 2 light tubes 1 for T12 and 1 for T8 to use for this part of the project. However, since my top-hat will be 24" internal with a 10" inlet, making it more that double height, I though that vibration of the outlet pipe especially if only supported at the top could be an issue. This would be affected by it's connection to the impeller housing as well as the long length inside the separator.
To reduce this, I have an idea of stabilizer rings extending down from the top. The inner surface of the rings would be lined with foam tape to support the outlet tube, which would reduce vibrations and harmonics of the pipe and negate any rattling caused by wood on metal.
This would also still allow removal of the outlet pipe for inspection and cleaning, as well as it would not be permanently attached to these rings so that while I experiment with height of the bell-mouth above the baffle I wouldn't need to completely open up the separator. Here are some pictures:
This is the whole separator as I have it drawn in SketchUp. I will be using metal for the tube, but I've made the external part of the metal a blue-glass color so it can be seen through. There will also be vertical supports around the outside, I just haven't drawn them in yet.
Please forgive my crudely drawn inlet. ::)
(https://i.imgur.com/GiWVUut.png)
Here it is without the metal tube..
(https://i.imgur.com/zjN5qw6.png)
This is just with the Top to show how the stabilizer rings will be attached. As you can see, there is no bell-mouth, as I didn't see the need to take the time to draw that in SketchUp.
(https://i.imgur.com/xNUIOja.png)
This one shows you a different view, with my inlet rings in place, and how I plan to mount the top-hat in the stand that I'm building for the full DC system. I will also be changing the orientation of the vertical braces so that there isn't one in line with the inlet.
(https://i.imgur.com/TEKxbEt.png)
So, what are your thoughts on stabilizing the outlet pipe in this fashion to reduce vibration and noise from harmonics?
Your outlet neck is pretty long so it might need some stabilization, but I can't recall anyone mentioning vibration of the outlet. The turbulance and noise I was getting until I added the air straighteners was coming from the blower housing. I'm sure it was the effect of the turbulent air on the blades of the impeller. I never noticed any vibration or noise from the outlet pipe, but mine is very short compared to yours. And mine is connected to the blower with a few inches of flex hose, so that should isolate the blower from the separator from the blower or vica versa.
It's possible that your stiffener could act on the spinning air and cause some turbulance that would not be beneficial. I think I would try to avoid it, but build your separator in a way that allows you to add it later if needed. Another potential problem is long shavings getting hung up on the stiffener. My outlet neck has a pretty good layer of fines stuck to it from use over time, so waste does get attached to even a smooth pipe.
Quote from: retired2 on February 19, 2018, 06:40:02 AM
Your outlet neck is pretty long so it might need some stabilization, but I can't recall anyone mentioning vibration of the outlet. The turbulance and noise I was getting until I added the air straighteners was coming from the blower housing. I'm sure it was the effect of the turbulent air on the blades of the impeller. I never noticed any vibration or noise from the outlet pipe, but mine is very short compared to yours. And mine is connected to the blower with a few inches of flex hose, so that should isolate the blower from the separator from the blower or vica versa.
It's possible that your stiffener could act on the spinning air and cause some turbulance that would not be beneficial. I think I would try to avoid it, but build your separator in a way that allows you to add it later if needed. Another potential problem is long shavings getting hung up on the stiffener. My outlet neck has a pretty good layer of fines stuck to it from use over time, so waste does get attached to even a smooth pipe.
Good points, thanks!
At this time, I plan to have my separator connected with hard pipe, not flex hose. I don't have any 6" flex, and it doesn't seem feasible to buy some just for a few inches for this connection. I plan to have slots for the motor housing attachment to the frame that the system will be mounted on.
This will allow for height adjustment of the outlet pipe in the separator and also for disassembly for any needed maintenance or upgrades, such as possibly upgrading the impeller to the rokon 60-200 that many have done to the HF units like I have.
I will build it without that stabilizers to begin with and see how it runs. I think one thing that might help mine is that the spin in both the impeller and the separator are both in the same direction.
I can't recall reading any discussion on the position of the drop slot in relation to the inlet on double-height separators.
In single height separators, the slot begins 120° after the inlet and continues around until ending just before the inlet. In a taller separator, the dust will drop to the level of the baffle and slot much later, after spinning around the perimeter of the separator some distance. Should the position of the solid portion of the baffle be changed based on this? Does it matter where the slot begins in this case or is it enough that it is present to de-couple the air below the baffle from the air above the baffle?
I'm raising this question because your steel sides will not allow you to observe the separator in operation, and if it does matter, it would be good to be able to change the position of the baffle.
Quote from: Alan H on February 19, 2018, 07:29:56 AM
Quote from: retired2 on February 19, 2018, 06:40:02 AM
Your outlet neck is pretty long so it might need some stabilization, but I can't recall anyone mentioning vibration of the outlet. The turbulance and noise I was getting until I added the air straighteners was coming from the blower housing. I'm sure it was the effect of the turbulent air on the blades of the impeller. I never noticed any vibration or noise from the outlet pipe, but mine is very short compared to yours. And mine is connected to the blower with a few inches of flex hose, so that should isolate the blower from the separator from the blower or vica versa.
It's possible that your stiffener could act on the spinning air and cause some turbulance that would not be beneficial. I think I would try to avoid it, but build your separator in a way that allows you to add it later if needed. Another potential problem is long shavings getting hung up on the stiffener. My outlet neck has a pretty good layer of fines stuck to it from use over time, so waste does get attached to even a smooth pipe.
Good points, thanks!
At this time, I plan to have my separator connected with hard pipe, not flex hose. I don't have any 6" flex, and it doesn't seem feasible to buy some just for a few inches for this connection. I plan to have slots for the motor housing attachment to the frame that the system will be mounted on.
This will allow for height adjustment of the outlet pipe in the separator and also for disassembly for any needed maintenance or upgrades, such as possibly upgrading the impeller to the rokon 60-200 that many have done to the HF units like I have.
I will build it without that stabilizers to begin with and see how it runs. I think one thing that might help mine is that the spin in both the impeller and the separator are both in the same direction.
Regardless of matching air rotation, you should still use an air straightener. Spinning air entering the blower reduces fan efficiency, and strangely, air that is spinning in the same direction reduces air flow more than when it is opposing.
Schreck, good questions. I've often wondered whether the positioning of a baffle makes any difference in a 2X separator. After I added the bell mouth to my separator I became more aware of the waste stream circling in somewhat of a sine wave pattern. I'm not sure why, but that would suggest that the position of the slot is not all that important in a 2X build. On the other hand I wouldn't want to chance randomly placing the slot in a 1X build. I think the closed area needs to be where the air enters the chamber, and Phil came up with that configuration after a lot of testing so I accept it as gospel.