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Directly below the key-bed is the main valve chest or stack,
with the tiny pneumatic motors (not visible) that operate the piano
action on its backside. The piano action is barely visible behind
the duplex roll-changer assembly.
Below the main stack are various piano expression devices, and
at the bottom of the case is the vacuum pump (technically called
a feeder bellows). The motor (not visible) to drive the pump's crankshaft
is located on the exterior back-side of the instrument.
The small black object just below the key-bed at the far right,
with the three red felted sliding valves, is the wind-motor, which
powers the forward playing motion of the music rolls.
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