Unfortunately, you do not need a check valve for your player piano.
The bellows or the stack or both of these are so leaky that only
a complete restoration will allow you to pedal this piano and actually
play it.  If you remove the motor and plug the hose and there is still
no way to pedal it to play the music, then there are other leaks, and
likely many of them.

Doug L. Bullock
thepianoworld.com