Cyclone Experts?

[Mac McAtee]

Can anyone tell me the effect of changing the length of the tube that goes down through the cylindrical part of the cyclone.

If you make it longer so it extends down into the cone area, I would assume that it would start sucking the dust that you want to drop out, back into the air stream. What happens if you make that tube shorter? Right now mine is cut even with the transition point between the cylinder and then cone.

I get small pieces of wood that are in the cone going roundy roundy and they don't drop, I hear them hitting the wall of the cone. If i leave the blower on for 20 min. they are right there the whole time. I can make them drop by closing all the air gates or by shutting the blower off.

Just wondering if I shorten that tube an inch or two if that will allow them to drop. Any ideas? I don't want to rebuild my cyclone but if a simple tweak will get that annoying racket gone it would be nice.

[Chris Padilla]

http://cnets.net/~eclectic/woodworking/cyclone/index.cfm

Perhaps some light reading of this site might help you out or at least point you to a man who might help you out.

[Bill Pentz]

Can anyone tell me the effect of changing the length of the tube that goes down through the cylindrical part of the cyclone.

...

Mac,

After lots of experimentation the folks at the Cotton site who did a lot of the latest in cyclone research determined the cyclone outlet should project 1/8 the diameter of the upper outer cylinder below the bottom of the inlet. Anything shorter and the air tends to "turn the corner" and provide poor separation. Anything longer and the cyclone outlet, as you said, tends to pickup dust from the separation process.

They also came up with making that outlet diameter ideally being the same outer cylincer diameter, they call it D, divided by two or D/2. Their experiments that strove to provide maximum separation of fine dust also determined a rectangular inlet sized D/2 x D/4 made for the best inlet and least turbulence. Turbulence kills cyclone efficiency in terms of both fine dust separation and overall resistance. Typical hobbyist cyclones add about 5" or more resistance. By using the neutral vane that can be cut in about half. By using my design with tilted inlet and air ramp you can get that resistance down to under 1". That becomes important when you realize that it takes about 3/4 hp and another inch of impeller diameter to overcome every 2" of additional resistance.

bill