It sounds as if Steven Hager has tapped his suction box into the wrong
place.  If he has installed a "T" connection in the hose that leads
from the pump to the stack, he has bypassed the cut out box which
prevents vacuum from reaching the stack, thus allowing the piano to
play during the rewind mode.

This would also account for the air motor not getting sufficient vacuum
to rewind the roll.  The cut out box would be closed in the rewind mode
preventing vacuum from reaching the air motor.  He should check to see
if the sliding block inside the cut out box is seated properly.  Since
vacuum was applied in the opposite direction from the way the cut out
box was designed, the block may not be sealing as it should.  This may
explain why the piano plays in rewind after the suction box is turned
off.

There should also be a one-way valve in the suction box which will open
when it is on and will close when the box is off.  When the piano is
played using the foot pump, vacuum will be lost through the suction box
if there is no valve present.  The correct way to install a suction box
would be to tap into the pump directly at a point where vacuum is
always present, before it reaches any other components in the system.

Bob Moore
Orlando, Florida