poor quality 90 degree fittings for dust collection

I dropped by the dealer today to pick up a 90 degree 4" ell for a temporary dust collection setup. I've never purchased in PVC dust fittings before. This was a Jet part number, but I think its the same universal Taiwanese-made fitting that everyone sells (other brand Woodstock?). It looked like reasonable quality, then I looked inside of it. Expecting a nice smooth sweeping curve, I was shocked. The inside of the fitting appears to be two pieces of PVC that have been cut on a miter and bent enough to come together. The outside of the ell is simply a nice looking shell. Its not smooth and it actually swages down to restrict the flow - not exactly what you want for a nicely designed smooth flow network.
Bob
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I'd take it back. If you read up a little, 90 deg bends are not really optimal anyway, you may be better off just using tubing to make the largest bend you can afford in your space (or hook a couple 45's together). Ideally, the tubing would be straight for the highest possible flow rate - every bend you add lessens your cfm.

temporary
nice
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I have read up and done extensive calculations. There is a balance between ideal flow conditions and making things fit in the shop. A 90 degree ell doesn't add that much drop. Its almost academic. What is really surprising (but not if you think about it) is the drop associated with flexible dust collection hose. A 2 foot length of flex hose has twice the drop of a single 90 degree ell. Most people use flex hose to turn corners. That's far worse than using a well made 90 degree fitting.
Bob

largest
Ideally,
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between
single
worse
But you shouldn't really be using 90's anyway. Mainly because it is a potential clog point. You should be using two 45's to round out the corner.
Roy
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Good point, Roy.
Bob Davis

ell
surprising
dust
corner.
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corner.
If you're using regular DC fittings, they are already "high flow" design. If you're using 4" PVC, (2) 45's work better, or find a local plumbing supply(NOT a BORG) and get high flow 90's(wouldn't know this, but SIL is commercial plumber, and our code calls for high flow 90's in sewer lines).
--
Nahmie
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On Sun, 15 Feb 2004 15:21:29 GMT, "Bob Davis"

I looked at the commercial fittings and was similarly underwhelmed. 4" light sewer pipe is much higher quality.
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Use standard borg plastic pipe fittings. Its cheeper. Now the sizes are a little off for the connectors but I watched a show on TV where a guy did custom pipe work with a heat gun. Aparently with a little bit of heat you can stretch, shrink, bend and shape PVC just about anyway you want. He took a piece of 2 inch and warmed it up and made a 2 - 4 reducer by using a broom stick handle to slowly encrease the size of the pipe till it fit in a 4 inch fitting.
If he can do this the slight 1/4 inch change needed to get standard 4 inch PVC to fit into duct collector ports should be a sinch.
Sometime I think it is a plot. Dust collector and shop vacumn fittings are intentially made just a little bit different from standard PVC so you cant use the cheep high volume stuff.
Now I caution you that I haven't tried this yet but I am going to. After all a couple of dollars worth of PVC should provide you with plenty of stuff to practice with. And if it doesn't work out then all you wasted is a little time.
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You might consider doing that in a well ventilated place. See toxic fumes warning at http://cnets.net/~eclectic/woodworking/PVC.html
David Merrill

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Great web site. This is just what I was talking about. I will definitely bookmark this one.
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I couldn't stand it. I happened to have a heat gun that I've used for years for heat shrink tubing (electronics wiring). I wondered if it would enough output. I needed a 4" x 4" square nozzel that adapts to 4" S&S pipe. So I took a 4"x4" fence post and put a 10 degree taper cut on four sides to make a jig. Then I took a scrap of pipe and began heating it. I could tell when it "went rubbery" and slipped it over the end of my wooden jig. Voila! I had a perfect nozzle ready to hook up to my dust collection piping.
Bob

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Cool! Sometimes all it takes is to do it!
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