Jumping in a bit late on Joseph Osborne's discussion from MMD 141203,
I am curious about how and where he measured the 40" vacuum before
a series of chords resulted in 6" vacuum and notes failing to play.
More importantly, if the 40" is the stack pressure before the chords
play, where [in what position] are the manual control levers?  How did
the stack get up to 40"?  At stack suction of 40", normally the piano
will be very loud.

If none of the levers had been moved to increase stack pressure, it
appears as if the "88-note pneumatic" is terribly out of adjustment.
(Since I have very limited experience with the upright version of the
Duo-Art, "88-note pneumatic" may be the wrong term.)

The situation described by Joseph fits perfectly the performance of
a leaky knife valve.  In other words, the only reason 40" of vacuum
exists while there is no demand is because the leaky knife valve
allows the pressure to increase well above the zero level.  Then, when
large chords play, that pressure is immediately depleted and, since
the knife valve is almost closed, there is little compensation for the
large demand.  The demand of the notes playing exceed the supply
through the leak.

Several MMDers had already offered suggestions.  I'd like for Joseph to
tell us how he fixes the problem, when that time comes.  In my opinion,
no reservoir is needed.

Bob Taylor
Missouri