Valves have mystified many a rebuilder for years: how to get them
airtight, how much travel, how not to have greenish slime form later.

First off, the typical valve travel in many players is .032" to .035".
Simplex and Coinola are much tighter, such as .028".  The valve travel
is determined pretty much on each piano.  If the valve travel is too
much then the valve will hiss as it closes and opens.  If too little
then the pneumatic will not close quickly enough.  I start with too
much travel and reduce the travel until the hiss is gone.

If the valve is going to seat on brass then I lacquer the seat to help
reduce the green slime.  If I know the leather has to be thin, as pouch
leather, then I use the smoothest side to seat against the metal valve
seat.  If the leather is going to seat against wood then I use the suede
side out.  Smooth side seats against metal and suede side seats against
wood.

Don Teach
Shreveport, Louisiana