Dear Howard and MMD group,  In the Pierre Eich Solophone that we
restored for the Sanfilippo Collection in 1994, the main pump has
a vacuum regulator valve on the bass end, acted upon by two opposing
pneumatics.

The bottom pneumatic is always connected to constant regulated stack
suction, and it controls the normal playing level.  The top pneumatic
pushes down on the valve whenever the second hole from the right end
of the tracker bar is open, increasing the suction level.  (This
tracker bar hole also controls the sustaining pedal and swell
shutters.)  The farther shut any pneumatic is at rest, the less force
it is able to exert.

To regulate the normal (softer) playing level, adjust the leather nut
on the valve stem that is lifted by the lower pneumatic.  Turning the
nut downward on the valve stem will cause the pneumatic to be farther
open relative to the working position of the regulator valve, increasing
the pneumatic's strength and consequently the overall suction level and
loudness.  Adjust this so the instrument plays as softly as possible
without dropping out any notes (or single-punch snare drum taps in a
Solophone with drums).

Suction from the piano stack also plays the pipe chest setoff valves,
so lowering the "normal" level too much will cause pipe notes to drop
out.  Because the lower pneumatic counterbalances the suction in the
pump, it acts as a spring but it provides instant feedback according to
the vacuum level in the piano stack.

The setting of the upper pneumatic isn't as critical, but it too becomes
weaker when its rest position is farther shut, or stronger when it's
farther open.

Art Reblitz