Mr. Bullock questions the reason, and detail of connection for a 1" x
1" pneumatic mounted on the top side of the so-called spring pneumatic
attached to the main expression valve in some Ampico expression units.
["Enigmatic Pneumatics On Some Ampico A Actions", 020709 MMDigest]

The purpose of this 1" X 1" pneumatic is to slightly soften the
intensities when the sustaining pedal is on.

When the sustaining pedal is on, the force used to move the piano
action becomes less, because the pedal pneumatic has done part of the
work by lifting the dampers and thus reducing the amount of power
needed to play a note.

The 1" X 1" blocks are connected series, and tubed to a nipple
specially set in the top section of one of a pair of unit valves that
operate the sustaining pedal.  It is very important that there are
absolutely no leaks in this little system, or it will not work
properly.

Their adjustment is regulated by movement of the leather nuts on the
small rods connecting them to the spring pneumatic. The device attempts
to even out audible difference when the sustaining pedal is on or off.
The difference is very slight.

Bruce Clark