The rotary pumps installed in Duo-Art grand pianos were made in two
sizes: 15" and 17".  The 17" pump was installed as original equipment
in the later Steinway grands.  Early Duo-Art grands (those early ones
converted from the steamboat pump in a separate cabinet) would take
only a 15" pump because the wooden braces under the soundboard were
closer together and ran parallel to the bass strings rather than the
left side of the piano.

I had one of these converted early instruments.  With the belly cloth
in place it reminded me of a pregnant hippopotamus, as the piano
butchers never could get the pump up all the way.  There was a lever
for Normal-Soft-Dance whose position made no difference whatsoever.
You should have seen it do the Charleston!

With its smaller 15" pulley the pump did run a bit faster, but the
motor pulley was somewhat larger, though it appeared to be original.
I thought of slowing down the wind motor sprocket ratio to conserve
air flow, but never did.  The piano was sold with the hope that the
new owner would keep the wintertime humidity up to the point where
condensation would run down the window-panes, and would _never_ play
rock music until the instrument was rebuilt properly.

Jeff Wood