Hey John Kleinbauer, you have just discovered one of many valves that
use the same basic universal design for controlling gases or fluids.

The same set-up is in all water shut off valves on washing machines and
you will find the same principle in every electrically controlled gas
valve.  That's why furnaces and water heaters and such can run off such
a miniscule current.  It only takes a small amount of current generated
by the pilot flame (your basic thermocouple) to control about 35 psi
of gas pressure through this method.

I'm guessing that the player piano was one of the very first machines
to take advantage of this invention.

Tom Lear