I have a 1925 Vollmer grand with H.C. Bay Recordo action. It sound
very close to what you describe. The most obvious clue is the molded
Bay valve. You need not open the stack to find these valves - they are
also used in the accessory pneumatics in the drawer, as well as the
expression box. Some other identifiers from the Vollmer:
1). Wind motor is six-point, with opposing pneumatics, similar to a
Duo-art, but smaller. It is located on the right side of the drawer
2). Wind motor speed slide switch is located adjacent to the motor,
but governor pneumatic is located behind the stack, near the pump.
3). Left side of the drawer has seven buttons labeled "FF", "F",
"MF", "P", "Sustain", "Soft Bass", "Soft Treble".
I do not have any literature on this action, but the tubing is all