Pneumatic Stack in the
Ramey Banjo-Orchestra
(made by the Ramey Piano Company)

View inside the back of the Ramey Banjo-Orchestra, showing the main pneumatic stack (which mechanically interacts with the piano action).
The main stack not only contains valves that control the individual piano pneumatics, but it also consists of the actuating stickers, which push against the piano action whippens, causing the various piano note hammers to strike the piano strings.