Joseph Hyde asked:

> ... I seem to remember someone asking about Midi (or electric?) valves.
> What are the function of these?

Joseph, these valves are used to allow computer control of pneumatics
in the piano.  They are installed in the tubing directly behind the
piano tracker bar (snip the tube, insert the valve).  The valves are
opened and closed by electronic signals from a computer and controlling
device.  Such an installation does not interfere with normal operation
of the piano or player mechanism.