Miguel de Mattos wrote:

> The problems are at the secondary valves, for sure, because
> everything else is vacuum-tight.  These valves, composed of two
> metal discs, were in bad condition; they were refaced and tested
> one by one, and they looked okay at that time...

You can check your stack by using an electric suction box.  Remove
the primaries and spool box and tape up the holes going to the pouches.
You can't just remove the "L" shaped wooden channel board because you
must close off the supply to the primaries as well.

Use a vacuum gauge or manometer.  Set your suction box to a known
number, say, 30 inches water lift, and attach the supply hose directly
to the stack.  Open one of the taped up pouch holes to the secondaries
and take a reading at that pouch hole.  You should get 30 inches or
really close to it if your secondaries are sealing.  If not, it may not
be how you rebuilt it -- it also can be the leather used is too porous.
You will have to find a leather that seals well to get the airtight
player you want.

When testing the valves you can take the decks off, tape up the screw
holes, and listen with your stethoscope in the holes to the pneumatics
to find one or more leaky valves.  If the leather is leaky then all of
them will be leaking, but possibly not enough to hear.  By the way, the
outside valve must be as airtight as is the inside one.

A few decades ago, when we used vegetable tanned leather, we could find
a great looking piece of leather, use it, and expect the piano to play
like crazy.  For the last twenty years, though, I have had cat fits
trying to find leather that will not seep.  This is because we cannot
use vegetable tanned leather since our air quality makes it only last
6-12 years before it turns to powder.  We must use chrome tanned
leather which is made porous by its tanning method but it lasts 50
years.  Don't trust any leather.  Before you use it on valves, test it.

D.L. Bullock
St. Louis
www.thepianoworld.com