My guess is that your piano's action cutoff valve, which shuts off the
vacuum to the piano action, is inside the foot pump box, and you have
tapped  your turbine downstream of that valve (upstream, as the air
flows).  This bypasses the cutoff and keeps your piano playing while
the roll  rewinds.

When you go to rewind with the turbine, the air must flow backwards
through that valve to get to the roll motor (which is tubed directly to
the bellows), and since that valve doesn't like to pass air backwards,
you get slow roll action on rewind.


>> One other item: If I try to pump the piano with the foot pump only,
>> I get music but it's like running a relay race.  I don't see any
>> leaks, or feel any, but I'm sure there is one there.  Did I tap into
>> the wrong place?


This sounds like you don't have a one-way flap valve in your turbine,
to prevent your foot-pumped vacuum from leaking back out through the
non-moving turbine.


>> My second idea was to install a nipple right on the main bellows box
>> and feed vacuum just as the foot pedal would do.


That should work, since the original rewind cutoff valve would now be back
in play.  You'll still need that anti-backflow valve in the turbine feed.

Hope this helps
Mike Knudsen