Unit Type Pneumatic Stacks
Made by Operators Piano Company

Operators unit pneumatic stack with Bakelite top seats.

(Photograph courtesy of Don Teach)

Later Operators pneumatic stacks have unit pneumatics mounted on a vertical trunk board. Each unit contains one pneumatic, pouch, and valve, enabling each note to be repaired without disassembling the entire stack. This stack from an Empress Electric piano has Bakelite top valve seats.
Late unit pneumatic stack with adjustable brass seats.

(Photograph courtesy of Rob Goodale)

In most later Operators Piano Company stacks each unit pneumatic has an adjustable brass top valve seat threaded into a fiber ring screwed to the top of the unit.
Close-up of a single Operators unit pneumatic.

(Photograph courtesy of Dana Johnson)

Close-up of one unit pneumatic, with the three screws for the fiber ring removed for disassembly.
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