About 15 years ago I restored an upright Steck pedal-electric Duo-Art.
At that time I didn't know anything about Duo-Arts so, as a help to my
understanding, I prepared very some very complete schematics and tubing
diagrams -- every orifice, valve and tube in the expression system is
shown.  Even years later it has been a great help in trouble-shooting
problems on a piano.

Since it's too large to scan I would be happy to snail-mail a copy to
anyone interested.  Just email me directly.

Phil Dayson