How critical is the dia of the input elbow ?

[sportflyer]

I would like to build a Separator based on a 5 gallon pail .  With only approx 12 inches across the top ,   a 4 inch elbow is just too large  with almost no space between it and the output tube.  I would like to reduce the input elbow to 3 inches and use a shortened 2.25 inch Shop vac extension tube as the output . Would this cause serious performance problems? Too much velocity ?  Thanks

[Bulldog8]

I seriously doubt that you would be happy with a 4" elbow on a 5 gallon bucket. You would have to do a lot of trimming just to make it fit. A 5 gallon bucket is better suited to a 1.5"-2"

[sportflyer]

I will try 2 inch dia pipes because it's more suitable for a direct hook up to the  shopvac . 

[tvman44]

1 1/2" or 2' placed as close to the outside edge as you can.  Only need 4" if using a DC with 4".  For a shop vac the smaller size is suitable. :)

[sportflyer]

The original Thein photo show the elbow exactly at the transition point between the end of the drop zone and the beginning of the  platform so there is actually less dust travel distance than the 120 degrees.  I would have thought that the position of the elbow is such that the elbow output is just slightly pass the end of the 240 degree drop zone so the input dust  has maximum travel before the start of the drop zone.

[sportflyer]

I built the separator and tried it out . I believe it works very well except for some very fine dust which still goes through to the shop vac . I am not sure how deep the output tube has to be relative to the   input elbow. Right now I have it about 50 % of the elbow opening . Could this be too far in so there is some amount direct feeding from input to output ?  Perhaps a shield  around the input elbow would help?  Any advise ?

This morning ,  I modified the inlet elbow so i'ts closer to the top.  The elbow, inlet and outlet pipes have a snug fit to their resp holes because I hand routed a small rabbet so the pipes sit about 1/4 inch below the surface. I then glued them down with E6000.  The outlet pipe is just a snug fit so I can adjust the spacing of the pipe from the drop platform.  See pictures

[sportflyer]

Here are the pictures.