Doug says that the rule for adjusting the bleed size in a primary or
single-acting pouch valve is so that the pouch trips
when 1/6 of the tracker hole is uncovered.  This is the point where
the bleed plus pouch_leaking equals the flow through the tracker hole and
tubing. Note that this is a _static_ adjustment.  I would guess that
a repetition test would be the better way to wring maximum
performance out of any particular installation.

Over a year ago, I described to Doug how to build a pneumatic
Whetstone Bridge using adjustable needle valves purchased at the
Tropical Fish Store!   The setup helped him decide if the pouch leather
required replacement, and if larger or smaller bleeds were needed.
Bleed-size adjustment was necessary in some piano restorations where
particularly "tight" pouch leather was replaced with the
currently-available "leaky" variety.  I can supply description and
theory of this test setup if someone wishes to try it.

-- John Rhodes