My thanks to Pete Knobloch for his discussion on setting the Duo-Art
accordion pneumatics. The discussion gives me further insight into how
to get this thing working better.
The remark about springs has me interested. My piano (a Weber grand)
did the same thing (ramped up the vacuum levels too fast) with the old
(original?) springs. I have plenty of vacuum, have set the muffler
felt, rebuilt the accordion pneumatics and the expression box, and
replaced the springs. I have my springs set for the minimum tension
possible, that is to say that there is basically zero tension when the
unit is off. I remember from earlier articles that the springs are 1/2
inch, with .049" wire cross section. I guess the next step is to get
smaller diameter springs and try that?
Even with adjusting my accordion pneumatics to less than 1/16" per
step, my vacuum curve is more of a parabola than a straight line, and
my test roll tests at levels 2 and 4 do not pass the "do not play or
should play very softly test".
I'll get back to work and try smaller springs, and then reset the
accordion pneumatics and try Pete's procedure. Hopefully I'll get
a flatter curve and a total of 15/16" travel at level 15.
Thanks, everybody, for your responses