DC can for Top Hat Build.

[Acadia]

Hi, Great forum!

I am getting ready to build a top hat/vent outside for my 3HP double bag.  Planning to build something similar to Retired2's build (nice job!).  But I was looking at one of the cans from my dust collector and it would be a heck of a lot easier to use that instead of building one.  I would flip it over so the ring is above or cut it out.  It even has a square inlet :)

Duct size 6" = 28 square inch area
square inlet 5"x5" = 25 square Inch area
ID 19 1/2"
Height: 11" but modifiable as per your suggestions

So what do you think build from scratch or try and adapt this one?  It would be easier to use the DC but if it's worth starting from scratch I will build it

Questions
- does the baffle have to be level with the entrance to the chamber?
- is 19 1/2 ID big enough for that 3HP
- I'm sure I'll have more....

Thanks for your help!

[retired2]

I think Phil is better qualified than I am to answer most of your questions, but I'll make a few comments for you to consider.

First, I would be hesitant about making modifications from which there is no return.  What happens if it doesn't work and then you have to build a top hat?

Rectangular and square duct is not as efficient at moving air as round, so HVAC designs usually take that into account and upsize transitions from round to square or rectangular.  I don't remember the amount, but I think it is about 10%.  So, when I designed my rectangular inlet, I increased the total square inches by about 10% from the 5" round pipe.  Is this critical?  I suspect not even the least bit since the inlet is very short.  I just did it because I had the freedom to make my inlet size and shape anything I wanted it to be.

Inlet above the floor?  My guess is it will still work fine.  Take a look at my video and watch the waste stream as it spins in the separator.  You'll see that it spirals downward, and even in my relatively flat top hat design not all of the waste enters the drop slot in the first trip around.  So, I suspect if the inlet were an inch or two above the baffle, the waste stream might just take an extra turn or two before it drops out.

Before I started my build, I asked Phil about optimum diameter.  In fact, there is a thread I started with that title.  You can read Phil's response there, but in general, bigger pipes take larger diameters to avoid by-pass, i.e. waste getting to the outlet pipe before it gets a chance to hit the drop slot.  The I.D. of my separator is slightly over 19" and I think it would easily support 6" pipes. 

Sorry, my comments don't give you more definitive answers, but the beauty of a Thien separator is there is a lot of latitude in what will work.  Obviously, some designs are more efficient than others, but probably the biggest reason for not working is lack of air velocity resulting from leaks or simply an underpowered DC.

Good luck.

[Acadia]

First, I would be hesitant about making modifications from which there is no return.  What happens if it doesn't work and then you have to build a top hat?

I bought this DC used cheap and I can't really use it the way it is, so either way it's going to be modified.  I bought it for the motor and blower.

Rectangular and square duct is not as efficient at moving air as round, so HVAC designs usually take that into account and upsize transitions from round to square or rectangular.  I don't remember the amount, but I think it is about 10%.  So, when I designed my rectangular inlet, I increased the total square inches by about 10% from the 5" round pipe.  Is this critical?  I suspect not even the least bit since the inlet is very short.  I just did it because I had the freedom to make my inlet size and shape anything I wanted it to be.

This is what I see as the main advantage of building my own.  I would think that a tall rectangular inlet would introduce the dust along the wall nicely.

Does the height of the top hat play a big role?

There are lots of successful builds with 2hp motors usually with a canister filter.  With a 3hp motor and no filter there would be more airflow.  So with the added airflow, do I need to adjust the dimensions of the typical 2hp top hat?  Or maybe the same size would work just fine and perhaps spin a little faster and in theory separate better.  I might even need the extra resistance to prevent the motor from drawing to many amps as a result of no bag.  I guess it will be trial and error. 

Have I missed a post with someone that built a 3hp top had direct vent?

I will start by building a very basic one using the collector can and see how it works.  Might be all I need

Thanks for the reply

[retired2]

This is what I see as the main advantage of building my own.  I would think that a tall rectangular inlet would introduce the dust along the wall nicely.

Does the height of the top hat play a big role?

There are lots of successful builds with 2hp motors usually with a canister filter.  With a 3hp motor and no filter there would be more airflow.  So with the added airflow, do I need to adjust the dimensions of the typical 2hp top hat?  Or maybe the same size would work just fine and perhaps spin a little faster and in theory separate better.  I might even need the extra resistance to prevent the motor from drawing to many amps as a result of no bag.  I guess it will be trial and error. 

Have I missed a post with someone that built a 3hp top had direct vent?

I will start by building a very basic one using the collector can and see how it works.  Might be all I need

Thanks for the reply

If custom welded transitions were cheap, I would have tested several different aspect ratios for a rectangular inlet.  But they are not cheap and I decided on what I thought would be a good compromise in shape, and it turned out to work very well.  In theory, a tall narrow inlet introduces the waste stream against the outside wall where it separates best.  However, my gut tells me this is like a lot of things, carry it to extremes and it becomes counter productive.

The height of the separator obviously affects the volume.  If you get carried away and make it too high, you could reduce the air speed to the point where it is no longer effective at separating the waste, especially fines.   

I don't know how a 3HP DC impacts the conventional sized separators.  It might be more useful to know the CFM and SP ratings of your DC.  My guess is that you will be fine with a conventional sized separator, and if you had to make it a little larger for some reason, the extra power would allow you to do that.  I would not go smaller. 

I seem to recall several older posts about members who were planning to vent to the outside with no filter.  You'll just have to do a search to find those posts.

[phil (admin)]

I can't remember anyone doing a 3-HP ring-based unit w/ direct vent.

Looks like you're going ot be the first.   :)

[Acadia]

Well I just finished my build and honestly I am a little disappointed.  The separation is simply amazing but there is too much loss of suction.  I might have messed up something in my build?
I would say the loss is almost 50% just by feeling the suction at the inlet.  It sounds like the air is too turbulent in there.  I also measured the amps of the unit to see what the loads were like.

Motor is rated at 17 amp (3hp 220v)
Just the blower nothing connected I got a reading of 17.8 amps
Connected with the baffle and no plumbing 11.3-11.5 amps

- Pipes are all 6"
- slot is in correct position
- top pipe is 3" down into top hat
- I took trash can off and duck taped the slot just to see if it was due to a leak down there, it wasn't

So what do you think is wrong?  ( or is it normal to have that much loss)

- the diameter is 19 1/2 but the height is 11" perhaps it would be better to make it shorter? Less turbulent ?
- I made the direction of spin for the separator the same as the direction of the impeller, correct?
- the inlet to the separator is square and at 4.75 x 4.75 is slightly smaller in area than the 6"
- I used the existing dust collector can to save time but I might have been better off custom building it

Thankfully my DC has its own little outside room so fine dust is not an issue.  If I cant find a solution I will just throw the dc in there and use it as it was intended.

Any ideas?  Havent givent up on the baffle yet, that separation is just amazing.

Thanks



Sorry no pic, can't figure out how to add them with my iPad

[RCOX]

Acadia, I didn't measure amps but after I completed my rebuild, I had the same results as you did. I have replaced all my ductwork with 24 gauge 6" click together stove pipe, changed my sharp 90's with 30 and 60 degree ells etc. Using the old hand in front of the duct trick I thought I had considerable loss so I made a home made manometer and was very dissapointed in the amount of loss. Without the separator in place I pulled 10" of suction, then I installed the separator and the suction fell to 6". Don't know where I went wrong but the results tell the tale. If anyone has any ideas please tell me.

On sawmill creek site, I saw a cyclone separator from an Ebay seller. I have also looked at the super dust deputy from Onieda. My question is, will the suction loss be comparable? Is this loss normal when we add the separator volume inline before the dc?

Help.

Raymond

[Acadia]

Rcox,

In my setup I have the blower directly above the top hat.  So really the longest pipe in the system during the testing was only about 6" long and I have similar result as yours.  I also looked at the Oneida super dust deputy.  I did get their mini dust deputy for my vacuum and there is a fairly significant amount of sucction loss with the deputy as well, although not as much as my DC setup. So I think it's just the nature of the beast; to get separation there must be a loss in suction/CFM.  I knew this going in, just didn't realize how much.

I was amazed how well it separated all the sawdust and junk I threw at it.  Nice work Phil!

[pitbull]

I think you figured out your problem... Your inlet is to restrictive..you are starving the beast. Also the height might be adding to the problem.

I made mine just over 6".....just taller than my inlet and it performs very well. I am sure there is some loss in suction, but I can not tell the difference and neither do the machines.

hope this helps
http://www.jpthien.com/smf/index.php?topic=429.0