I don't bother with those whimpy tracker-bar pumps...  I plug in the
trusty Suc-O-Lux, set it on the low setting with a horse-hair brush,
and lightly/carefully go over the bar once in a while.  Sure enough,
those dead notes come back to life! My tracking-mechanism pneumatic
tubes on my Autopiano are filtered with fine brass screens at the
inlets, but the tubes to the playing primary valves aren't filtered.

If I had the time and equipment, I'd experiment by making a box with 88
inputs that each lead to a 0.5^3 dimentioned chamber, then immediately
exit 88 outputs on the back.  This would go in-line between your
tracker-bar and your stacks primaries.  In each of the small cavities
would be placed a brass-braid filter, or a lightly tufted wad of
cotton.  The top of this box would disassemble with a few screws for
annual cleaning/cotton replacement, just like my tracker inputs are
designed to do.

I can imagine some possible drawbacks: Added resistance causing
low-power passages to miss playing, increased line capacity causing
signal delays or other undesirable phenomenon, added manufacturing $$$.
Can anyone think of reasons why manufacturers haven't bothered with a
filtering mechanism for these holes? If the theory's good enough for my
tracker-mechanism's inputs, why not the stack?

- K a r l   B.   E l l i s o n
  Ashland, Massachusetts  U.S.A.
  KBELLISON@aol.com
  http://members.aol.com/kbellison/kbe.html