John Tuttle asks about operating player pianos at high altitudes.
This is an intriguing subject, and it would be good to hear from anyone
doing just that.  However, my own thoughts are that since the pumps on
the piano are producing a pressure differential from input to output
according to the springs, it should follow that the air pressure/vacuum
produced is constant.

Problems do begin to arise in pipe organs however, on a hot day when
the air is lighter.  Although the pressure is constant, the lighter
(thinner) air is more easily blown through the pipes' flues and
therefore the bellows tend to flag or even go flat altogether because
they cannot blow the volume of air required to keep up the pressure.
Could it be that this applies equally to any valve operated instrument
such as a piano, and so experiences the same symptom?

Regards,
John Page, UK