Everyone who has responded to this question has answered the question
of how it might be done, to my mind.  But I would like to add a few
other considerations.

I am not exactly sure how high a pressure might be obtained by pumping
the treadled Duo-Art, but I suspect it would have a maximum pressure of
about 18 inches instantaneously, and with hard pumping one could manage
16 inches for a stretch.

I know I am going to be told they are able to get 35" any time they
kick those pedals.  If so, then I just say that is physically
impossible.  Not that the momentum of a water column is not able to
instantaneously bounce that high.  It can.  But what it bounces to
and what it achieves in an actual correctly done pressure test is
different.

That equates to "nominal" low pressure in all electric pumped
reproducers.  In the Marquee foot-treadled Ampico, you are able to
achieve the highest pressure of all, because of the design of the
two feeders, which are very small 8" square bellows (about 120 cu
inches/full pump max each) operated by long cast iron levers which
reach all the way down to the floor of the piano, allowing the foot to
apply a momentary kick that will possibly reach 20-22 inches or so for
perhaps a two-three note chord.

That's pretty good for foot treadling.  But to maintain 22" in a
Marquee (say, during a long, loud and busy passage in a Hungarian
rhapsody) is close to impossible unless you have the legs of a long
distance runner and use your piano to exercise on.

The Ampico Marquee doesn't use the spill system, so you are not
vacuuming the room like you would do in a Duo-Art.  All your energy is
going directly into the music.  That gives you a chance to rest.  It
also uses flat metal springs instead of "crescendo" bellows and spring
pneumatics, greatly decreasing the air demand which maintains the first
intensity settings pneumatically in the standard Ampico.  However, they
are no longer proportional or accurate.  But it's good enough for
treadling, because your feet are not exactly the perfect power source,
either.  And in either the Ampico or the Duo-Art, the pianolist puts
in the majority of the musical inflections and accents with his feet,
anyway.  Maybe nobody else notices it, but he does, because he is doing
it and anticipating the result.

When most reproducing pianos operate normally, their pump is running at
a nominal 20-22 inches of vacuum pressure.  That gives them plenty of
reserve to instantly provide the first single forte.  Mezzo-forte is
usually achieved at between 16 and 20 inches of vacuum, depending.
So those who treadle reproducing pianos should not expect an awesome
concert for others in the room, but something approximating a salon-
style performance.  For him, however, it may be a different degree of
perfection.  Those who treadle and twiddle are always the most
impressed with the performance, and I think that's just fine.  These
things are supposed to be fun!  If pedals and levers get you there,
then more power to 'em.

Craig Brougher

 [ Many times I became disgusted with the performance of a Duo-Art
 [ piano (admittedly in "average" condition) and so I played the same
 [ roll at my venerable Aeolian Themodist vertical piano, incorporating
 [ _my_ expression ideas.  Yes, it was hard work play loudly; the
 [ Magnehelic gage reading stack suction sometimes averaged 25 inches WC
 [ for a few seconds.  (The pedal exhausters on my Themodist are fairly
 [ small, so they don't deliver much flow, but they can produce relatively
 [ high suction.)  It was very satisfying musically (loud, too!) and
 [ good physical exercise!  ;-)   -- Robbie