Round to rectangular inlet question.

[Dougp28704]

I was playing around last night with 5? dia duct. I put pieces of rectangular mdf in the end and used a mallet to form the round to rectangular. It doesn?t look bad. The only thing is, the perimeter of the rectangle is the same distance as the diameter. But the area is smaller. I don?t want to spend the money to have one made like Retired2 did. Although that is sweet. I assume retired2 made the area of the rectangle the same square inches as the area of the diameter. Would I be better off just having a round inlet, or the transition I made?

[retired2]

No, I made the area of the rectangle about 10% larger than the area of the 5" round duct.  That decision was not abitrary, it was based on some HVAC engineering data that says square or rectangular duct is not as efficient as round, and needs to be 10% larger in area to be as efficient.

Now, when you consider that the rectangular portion of my transition piece is very short, it might make very little difference.  However, I decided not to introduce a "choke point" in my system, regardless how small,  when it made absolutely no difference in the cost to fabricate the transition piece or the cost of the separator. 

[Dougp28704]

Do you think I would be better off leaving it round? I can?t afford to have one made. Well, I shouldn?t say that because I don?t know the cost. But seems like it would have to be pretty high.

[retired2]

Do you think I would be better off leaving it round? I can?t afford to have one made. Well, I shouldn?t say that because I don?t know the cost. But seems like it would have to be pretty high.

I've got myself convinced that the best configuration for an entry port is rectangular, taller than it is wide.  I'm also convinced the heigth of the rectangle should be the inside heigth of the separator.  Sorry, I have no proof of this, but a rectangular inlet creates less turbulance than a round one and it keeps the dust laden air closer to the outside wall and drop slot.  These are the same arguments I made in my original build thread.  The videos show the rectangular inlet in action. 

[Peter]

Why not get a length of 5" duct, and cut it length-wise, 180? opposite the seam.  Then make the rectangle of mdf as you did, but with your desired dimensions. Place the duct over the form, just as you did, and pound the thing into shape.  This should leave you with two long triangular gaps...which you could easily patch with a piece of flashing and pop rivets.

That's what I plan to do. :)

[Dougp28704]

Retired, I have read your thread multiple times over the last few months. I agree that your setup is optimal. I was just trying to save some time and money.

Peter, I will give your plan a try and let you know how it works out for me.

Thank you for the responses.

[retired2]

Retired, I have read your thread multiple times over the last few months. I agree that your setup is optimal. I was just trying to save some time and money.

Peter, I will give your plan a try and let you know how it works out for me.

Thank you for the responses.

Take Peter's suggestion a step further.  Use a 6" piece of round pipe rather than 5", and beat it into a rectangle.  The extra material of a 6" round will give you a rectangle that is larger in area than 5" round, which is what you want.  Then at the round end of the 6" pipe install a 6"x5" concentric reducer.  There you have it, a pretty decent poor-man's 5" round to rectangular transition piece!

[Peter]

Most reducers are pretty abrupt.  I.e.: they have a transition angle of about 45?.  Since we worry about every little thing that might cause turbulence that will slow down FPMs, I'd worry that such would occur in that transition.

Y'know, if I had another $1000, I'd have a 5-hp cyclone and use 6" duct.

But I don't, so I'm gonna finesse the HF install.

First, though, I have to build storage cabinets to get all these miscellaneous tools off my floor so I can put a ladder in the shop to install the duct.

Does it sound like I'm procrastinating?
You be the judge. :)

[retired2]

Most reducers are pretty abrupt.  I.e.: they have a transition angle of about 45?.  Since we worry about every little thing that might cause turbulence that will slow down FPMs, I'd worry that such would occur in that transition.

True, reducers tend to be very short transition pieces, but in this case it is an increaser rather than a reducer, and it is followed by hopefully a smooth round to rectangular transition, so I think the negative ipact will be minimal.

[RCOX]

I think it was on Oneida's site that I saw long tapered reducers that will eliminate the abrupt angle transition, if you are worried about turbulence. I am sure other dc sites carry the same thing, but like everything alse, it comes with a price.

Raymond

[retired2]

I think it was on Oneida's site that I saw long tapered reducers that will eliminate the abrupt angle transition, if you are worried about turbulence. I am sure other dc sites carry the same thing, but like everything alse, it comes with a price.

Raymond

I think I've seen those somewhere too.  It's possible that with a long increaser, you could beat the 6" end into a rectangular shape and you're done.  Of course, things are rarely that simple.

[RonS]

The 6" to 5" tapered transitions are available from Oneida, but they are about $25 plus shipping.

Here is my transition it is also easy and cheap to make.

It is 5 15/16 by 3 7/16 (20.4 SqIn) on one end and 5" (19.6 sqin) round on the other, it is about 12" long with the extensions. Here is the post with some instructions and some pictures. (These are inside dimensions)

http://www.jpthien.com/smf/index.php?topic=637.0


It can be made from a 12X24 sheet of 26 gage sheet metal which can be bought at most hardware stores.

I've attached a PDF file of the full scale drawing printout needed to make this transition.

If you print this drawing set your printer to paper size 8.5 X 11 portrait with no scale factor, don't use fit-to-page. After printing, make sure it is full scale, check by measuring the dimensions at the bottom of the drawing, they should be right on.

You will notice that this drawing contains 3 sections. The transition is the 8" section in the center where the diagonal (DL) lines are drawn. The piece at the top is the 5" round section extension (about1 3/16). The section at the bottom is the rectangular attachment (about 2 3/4). The 3/8" rectangular pieces  on the sides and where it says "leave this tab" are for attaching it together once the cutting & bending is done.

Here is how to use the drawing: (reference the post above for pictures)

   1. Clean your sheet metal (SM) before you start. Tape the three pieces of the drawing to your SM, keeping the top section as close to top of the SM as possible, make sure the long tab at the bottom right fits on the SM. Use a straight edge to align the sheets using the diagonal marking lines. (First picture in post)

   2. Use a sharp knife to mark through the paper where each of the DL start and end. At the bottom mark the straight lines to the bottom of the SM, the 3 middle lines are bend lines and the 2 on the right & left are cut lines. . Cut the paper away around the top, right & left sides marking the SM as you cut, these will be the top, right & left cut lines. (Second picture in post)

   3, When everything is marked to your satisfaction remove the paper and using a straight edge and knife finish marking the diagonal bend lines and the outer cut lines. I would use a black marker to mark the cut lines. (Third picture in post)

   4. Cut along all the outer cut lines. At the bottom cut the arcs to where it is shown on the drawing. (Forth picture in post)

   5. Bend along the diagonal bend lines, each bend is only about 15 deg, try not to bend into top section any more than necessary since it needs to be round when your done. The 3 center bend lines at the bottom are 90 deg, bend them last. I used 2 pieces of angle iron clamped to the bench to do the bending.

   6. Bend the 3/8 tabs on the right and left so you can attach the thing together. I used a 5" round and 5 7/8 by 3 7/16 wood template on the inside when during the final assembly.

I also made sure it was going to fit into the Thien TopHat inlet and that I could attach a 5" pipe inside the round end. I used small rivets (hammer & anvil) to assemble the seams then taped them all with AL HVAC tape. (The last 3 pictures show the finished transition)

Remember the dimensions on this drawing are the inside dimensions so your outer dimensions will be these dimensions plus twice the thickness of your sheet metal.

If any one is interested I would be willing to create this drawing for a 6" inlet to about a (6" X 5") 0r (7" x 4.5")  ?? outlet.   



Looking at this post by dmh. I like his transition and it looks really easy and cheap to make.


http://www.jpthien.com/smf/index.php?topic=666.0

[Dougp28704]

RonS,

I saw your instructions a while back. At that time I was a bit intimidated. But I was reading it over again the other night. I decided that I will use your plans.

Thank you.

Doug

[Bulldog8]

If any one is interested I would be willing to create this drawing for a 6" inlet to about a (6" X 5") 0r (7" x 4.5")  ?? outlet.   

Ron, I am considering making a 6" round to rectangle inlet for my separator. I'd appreciate a PDF of your drawing to do this. For my situation, I think that a 7" x 4.5" outlet would be best.

Thanks for the offer.

Steve

[RonS]

Bulldog8,
Here is a pdf file for 6" round to a 7"X4.5" rec transition. this will fit on a 12X28 piece of sheet metal. The rectangular section will be about 1.5" deep, the transition section will be 8" and the round section will be about 1.5".  The more you can add to the 12" dem on your SM the deeper the rec section will be. This file prints out on 6 sheets of paper in landscape mode. Print it out and past it to the bench and see what it looks like, use a straight edge to line up the sheets. make the dimensions shown on the drawing are correct on the printout.