After my last post on cyclones, I read some papers that
have raised questions in my mind about whether using
air ramps and neutral vanes in cyclones is a good idea. The
acutal quotes are below.
It seems like an inlet-vane or air ramp hurt the dust collection
efficiency quite a bit. Using either of these would mean that
the final filter needs to be cleaned about 3 times as often.
And presumably replaced 3 times as often.
Can anyone come up with a reason to use an air ramp in light of
Reference  has this to say about neutral vanes, which it calls
"Several modifications were made on the small-diameter cylcone in
attempts to improve its performance. ... The inlet-vane reduced the
pressure drop through the cyclone by about 60 percent. Unfortunately
it also reduced the cyclone collection efficiency. About three times
more material was emitted from the cyclone with the inlet vane than
from the unmodified cyclone."
Continuing on to air ramps, which it calls input helixes,  says:
"A cyclone with an inlet helix was tried next. ... This cyclone
with the inlet helix performed simalarly to the one having a flat
inlet vane. Both the pressure drop and efficiency were reduced
when the inlet helix was used. About two and one-half to three
times as much material was lost from the cyclone with the inlet
helix than from the unmodified cyclone."
Reference  is a preliminary report of a computer simulation
of a cyclone.
 says: "In the plan view of the cyclone streamlines air
makes one revolution in the barrel of the cyclone, then
makes an abrupt change in direction near the entrance (where
it collides with incoming air). This forces the dust-laden
air to make a tight turn inward and downward. The fact that
the air is leaving the dust behind at that point appears
to be more important to cyclone efficiency than the fact
that the dust is reintroduced into incoming air. This
alternate approach to understanding cyclone dynamics was
thought to possibly explain the results of an earlier
experiment attempting to prevent such reintroduction".
It then goes on to quote the material that I quoted
 Baker and Stedronsky. July 1967. "Gin Trash
Collection Efficiency of Small-Diameter Cyclones", ARS 42-133;
USDA Argicultural Reseach Service
 "Dust Cyclone Modeling and Validation" a presentation
made by Funk and Hughs at the 2000 ASAE Annual International Meeting
ASAE Paper no. 004026