[ Ref. John Tuttle in 23.05.28 MMDigest --

John, you are correct! The box next to the spoolbox is the primary
valve for the sustain unit. The drawings you send would be a correct
schematic for this piano player system.

You see the breather hole C on the top cover board. It needs no nipple
as it only lets atmosphere in to give a large gush of air to the large
sustain pouch below, which has no bleed.

All the early Aeolians had this primary valve for the sustain which
always have a regulator for the sustain pneumatic only. Some of these
primaries had Themodist valve attached to the right of it just like
Duo-Art does.

Doug L. Bullock
Alton, Illinois
tel. or text: 1-314-772-6676
https://www.thepianoworld.com/