I have occasionally seen Steinway Duo-Art uprights that have
a lever-operated five-position switch at the left side of the
levers that controls the player, such as play-reroll, tempo, etc.
I always wondered exactly what this lever does.  I recently bought
a Steinway Duo-Art with this control, and I can now explain what
happens as the switch positions are chosen.

I assume we know that as an accordion collapses, it pulls down
a rod connected to a piece of wood.  The Aeolian company added
a new pneumatic to the expression box, which I will call the
limiting pneumatic.  When this pneumatic collapses, it moves
a piece of metal so as to block this piece of wood that is
connected to the accordion from moving past a certain point.

Since the accompaniment accordion now cannot collapse all the
way, the accompaniment cannot get as loud as it could before the
limiting pneumatic was activated.  This volume level can be
adjusted.  The theme accordion is not affected.

Now, here is what happens when the five-position switch is
activated:

1) Concert:  No pallet valves are open
2) MF:       The limiting pneumatic works
3) PP:       Both the limiting pneumatic and the P (soft) pedal
4) P Pedal:  The soft pedal only
5) Dance:    One section of the accompaniment accordion is
             turned on. (your choice)

Randolph Herr