During a year period, my Duo-Art piano has been gradually playing
more weakly, something which I attributed to my unrestored Duo-Art
pump, which also has a somewhat too weak motor.  Or so I thought.

I didn't bother to restore the pump because it worked okay, and
unfortunately, I got the wrong size, a 17" instead of 15", which
doesn't fit inside the piano.  I planned therefore to exchange the
pump for the correct size, instead of restoring it.  The motor is 120
watts which is more than the 1/8 hp required for a 4-bellows pump.

Anyway, I have a vacuum gauge connected to the air intake to the piano,
and tried different things which surprised me, and since I can't find
my restoration manual for the Duo-Art at the moment, I have to ask you.

First of all, it seems like the motor and unrestored 17" pump is okay.
I reach a vacuum of just over 50"; if I block the air intake of the
pump then it stalls.

Before, I believe the measurement was a little over 40", when it was
connected to the piano "between playing of notes", with the roll running,
and now it is only around 20", and the piano doesn't play at all.

If I have no tape over the tracker bar the measurement is 10", and if
I tape all the holes the measurement is 20".  According to the hissing
sounds from the expression box, it doesn't seem to matter very much
whether none, a few, many, or all note holes are exposed or closed.
It doesn't matter much if the expression holes are covered, but it
matters some, when the left and right pedal bellows are operated, they
leak some air.

So it seems like the air instead of being redirected to the pneumatics
to the 88 notes, is leaking. The rebuilding of the right pedal bellows
isn't perfect, and the left pedal bellow is a generic bellow bought
from Player Piano company, and accounts for some leaks. But the left
and right pedal bellows work ok, and the leak from them is measured to
be negligible, as NO notes play at all, even if I block off the air
supply to those bellows and at the same time, stop the bellows motor
which runs the roll.

The expression box is tightly sealed as far as I know, when I did the
job, the two large expression bellows at the bottom, are completely ok,
and there's some more hiss if I manipulate them, but no difference if
I push together the expression pneumatics and/or operate the expression
valves. The expression valves refuse to even react, even if I only
uncover the holes belonging to them, in the tracker bar.  Even if
I close them, there's still not enough vacuum connected to the upper
part of the piano, to play even the faintest note.

So I suspect something has gone terribly wrong inside the expression
box, but what?  Can someone please advise me, as I am going to move,
(hopefully getting less sensitive neighbours, which means using the
piano more! :-) and right now I cannot find my restoration manual, and
the 'How to test and adjust' manual which I have, mainly deals with
already working pianos.

Thomas Henden,
Oslo, Norway