Re "Enigmatic Pneumatics In Late Ampico A Actions"

The little pneumatics should be tubed to the sustaining pedal
valves.  When the sustain pneumatic lifts the dampers off the
strings, there is less weight (in a grand) or spring tension (in
a vertical) counteracting the force of the stack pneumatics for the
notes that have dampers.  Consequently, the stack plays the notes
which have dampers a little louder when the dampers are lifted than
when they are at rest.  The compensator pneumatics lower the suction
by a tiny amount, counteracting this effect.

This is described and illustrated on pp. 159-160 of my book "Player
Piano Servicing and Rebuilding."

Art Reblitz