5" Fittings with a Thien Baffle???

[Adam Kaufman]

Does anyone out there use 5" fittings in a Thien baffle?

I've got an HF collector and I'm making a separator with a 30 gal. can and I'm having one heck of a time finding fittings! I can't find DVW in 5" and schedule 40 prices are outrageous. I've seen 5" elbows for over $100!!!

Lowes has the metal 5" adjustable elbow but, I was trying to find something with a smooth interior (does it matter?).

I'm willing to go with metal or plastic...

If anyone can steer me in the right direction, I'd forever indebted!

Here's what I've got so far...

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[Ryan Mooney]

Yep. My setup is a rather mish mash mix of:

5" stove pipe between the HF and the top hat
5" stove pipe coming out of the top hat
5" flex (grizzly.com) from the stove pipe coming out of the side of the connector to the machine
Rubber Fernco fittings to the machine
5" - 4" HVAC adapters on the 4" machines. I lined the connection bits of those with duct sealant to make the Fernco fit tighter (it slides inside the 5" adapters and over my euro 120mm connectors).


Not sure where you needed the elbow? Are you hard piping the whole setup? Hard pipe at 5" for any distance does get pretty difficult to find it seems. I couldn't find any plastic. You might be able to get most of it as stove pipe, but the leakage factor is high on the pipe-pipe connections with that (and I ended up gunking the seams on even the couple feet short run I have).

[Curt Harms]

Replace the cover of the HF blower with a sheet of plywood and cut a 6" hole. Make the 'top hat'- blower connection 6". If you're concerned that a 6" connection will move too much air and overload the HF motor, do you have or can you borrow a clamp-on ammeter? Check the amp draw of the motor and make sure it doesn't exceed the motor data plate number.

[Ryan Mooney]

Replace the cover of the HF blower with a sheet of plywood and cut a 6" hole. Make the 'top hat'- blower connection 6". If you're concerned that a 6" connection will move too much air and overload the HF motor, do you have or can you borrow a clamp-on ammeter? Check the amp draw of the motor and make sure it doesn't exceed the motor data plate number.

More concerning based on my experiments is that at 6" the HF unit didn't have enough airflow to keep the dust moving in the pipe (i.e. it was what I would consider "not functional"). This was with 10' of flex though so smooth pipe would be somewhat better.

[Curt Harms]

More concerning based on my experiments is that at 6" the HF unit didn't have enough airflow to keep the dust moving in the pipe (i.e. it was what I would consider "not functional"). This was with 10' of flex though so smooth pipe would be somewhat better.

I don't have the HF unit but I've read they have a smaller diameter fan so you may be right. In this case I don't believe there'd be any material suspended, just air, the material should have dropped out of the airstream into the can.

[Adam Kaufman]

Thanks everyone!

I went ahead and used 5" metal from HD. I'm waiting for the adhesive to set up now.

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I'm keeping my fingers crossed.

[Ryan Mooney]

I don't have the HF unit but I've read they have a smaller diameter fan so you may be right. In this case I don't believe there'd be any material suspended, just air, the material should have dropped out of the airstream into the can.

Yeah, if you're saying 6" from the HF->the top hat I'd agree there would be no harm. Probably not a lot of real gain either from the 5" factory inlet from what I can tell. The problem I saw was when I tried to go 6" past the top hat which didn't work nearly as well as I'd hoped.

[Curt Harms]

Yeah, if you're saying 6" from the HF->the top hat I'd agree there would be no harm. Probably not a lot of real gain either from the 5" factory inlet from what I can tell. The problem I saw was when I tried to go 6" past the top hat which didn't work nearly as well as I'd hoped.

Probably easier to find fittings especially PVC but it looks like the O.P. solved his problem. I can see where a smaller/less efficient fan would have problems with 6" ducting - not enough air velocity to keep material suspended.

[Adam Kaufman]

I'm the OP of this thread and I thought I'd just add something.

The Thien baffle I built works VERY well. 5" seems to be the way to go with the Harbor Freight collector. As it is, I'm separating at least 98%! I've got several cubic feet of dust/chips in the can, but the the bag might have a 1/4 cup fines...

Thanks all for the input!

[Jay Park]

I'm planning on replacing the 5" impeller cover on the HF DC with a 6" inch bell mouth.

Then I can use 6 inch fittings which I won't have to replace when I upgrade DC

[Adam Kaufman]

Jay, I thought about doing the same thing, but after a lot of reading, the consensus seems to be that the HF DC doesn't have a large enough impeller or the HP to keep dust airborne in a 6" pipe.


I'm planning on replacing the 5" impeller cover on the HF DC with a 6" inch bell mouth.

Then I can use 6 inch fittings which I won't have to replace when I upgrade DC

[Phil Thien]

Jay, I thought about doing the same thing, but after a lot of reading, the consensus seems to be that the HF DC doesn't have a large enough impeller or the HP to keep dust airborne in a 6" pipe.

This is one of those issues that I think depends on differences between HF units or something. Some have succeeded at using 6", some have failed miserably. I'm not sure what accounts for the differences.

I do think the #'s widely stated to keep dust entrained in an airflow may be very conservative (on the high side). I've kept pipes clear with lower numbers (during some experiments).

[Ryan Mooney]

This is one of those issues that I think depends on differences between HF units or something. Some have succeeded at using 6", some have failed miserably. I'm not sure what accounts for the differences.

I've seen a couple of different actual measurements of the HF impeller. I know mine if 9.75", but some others have indicated that theirs was over 10" so that may well account for the difference in behavior.

[Rick Thom]

I've seen a couple of different actual measurements of the HF impeller. I know mine if 9.75", but some others have indicated that theirs was over 10" so that may well account for the difference in behavior.
My memory is a bit hazy on this but IIRC this is a bit of the recent history on the HF DC.
If you search around a bit I think you will find information and threads about the change in size of HF impellers.. maybe 2 years ago when the units with the smaller 9.75" started to be sold. Some bought another brand's larger impeller which was an exact fit for the HF 2 hp DC so they just swapped out the small one for the large one which was nearly 12" dia IIRC. It just fit the housing without modification. The larger impeller made a huge difference in air flow and that's why the old units could support 6" pipe but the new ones struggle. There was quite a lot of discussion about different brand's impeller design and blade curvature and direction of rotation since they aren't all the same. The folks involved boiled it down to exactly what worked. I have forgotten which brand they used. They also had the part number so you could order it.
The replacement impeller wasn't cheap but still made the HF unit with the replaced impeller great value and a great performer.