I'd like to add that even today, pneumatic action is (possibly) lower
cost and much lighter in weight than an equivalent electrical bank of
solenoids or magnets.

Electric actuators require plenty of heavy and expensive copper wire,
plus heavy ferrous armatures.  Pneumatic wood and cloth are much
lighter and still cheaper, and could be assembled by automatic
machinery if the volume of production warranted.

To put it simply: Electrical actions are full of copper and iron.
Pneumatic actions are full of -- air!  And by raising the suction
level, small pneumatics can be made very powerful, without worrying
about the heat dissipation that plagues electricals.

Also, vacuum pneumatics develop their maximum force at the beginning
of their stroke, while electrical magnets or solenoids typically have
a weak initial pull and pull strongest at the end of stroke.  The
former is better for accelerating hammers and beaters and cracking
open organ pallet valves.  (OK, so the latter (electrical) is better
for fretting violin strings -- it's been done that way :-)

Perhaps someone who's worked with Pianomation or Disklavier can
comment on the weight of the "stack" compared to a good old player
stack.  Though to be fair, how about that 1950s vintage pneumatic
stack that the user placed over the keyboard?  It must have been light
enough to pick up.

Mike Knudsen

 [ The "Electrone" keytop player (pneumatic) needed two people to
 [ position it over the keys; so did the Marantz Vorsetzer.  An
 [ auto-transmission jack is needed to safely re-fit the solenoid
 [ action-stack into the Boesendorfer SE piano!  -- Robbie