In "Enigmatic Pneumatics On Some Ampico A Actions", MMD 02.07.09,
D.L. Bullock writes:

> I have two Ampicos with a 1" x 1" pneumatic mounted on the top side
> of the so-called spring pneumatic attached to the main expression
> valve.  <snip> I need to know what they connect to since the tubing
> was toast when I got to the pianos.  I am guessing they probably
> connect to the soft pedal pneumatic but I am not sure they would be
> desirable. ... Where do they connect and how are they regulated?

These were called by the company, "loud pedal compensators".  They tee
into the line between the sustain pedal valve and the sustain pedal
pneumatic so that when the sustain is activated, they are under suction
and slightly resist the up-push of the spring pneumatic, since they are
connected by a wire to the moving board of the spring pneumatics.  They
are not regulated in any way except by their position and the amount of
cloth on them.

The theory was that a note struck with the dampers raised was louder
than a note struck at the same intensity without the dampers raised.
The slight resistance offered by these mini-pneumatics counteracts
that.

They are very common on all "late A" Ampico grand mechanisms, 1927 to
1929, just as are the soft pedal compensator pneumatics in the stack.

By the way, the spring pneumatic is so called because in many very
early Ampico mechanisms, and in some Marque Ampicos, its function or
working against the intensity pneumatics is actually performed by an
actual spring and not by a pneumatic at all.  The crescendo mechanism
worked quite differently in these installations.

Dean Randall - from rather warm Puget Sound.