Robbie is right about the spring pulling open the Tempo regulator
pneumatic.  It could be a coiled spring, a single piece of spring
steel or two steel strips riveted together like a V.

They all do the same thing -- they pull the two wooden boards apart.
This regulator is usually found on the right side of the foot pump
assembly, but it may be a separate unit.

Has anyone mentioned the book, "Player Piano Servicing and Rebuilding,"
by Art Reblitz?  This will be well worth the money if you want to
understand and rebuild these older players.

Pete Knobloch
Tempe, Arizona