(Illustration from Presto, 1919)

Cross-sectional view of a Standard Player Action stack. The above stack design is for a standard 88-note player piano, but remove the upper primary valve chest and one tier of pneumatics and what remains is very similar to the two tier stacks installed by Smith, Barnes & Strohber in the majority of their Chicago Electric brand of pianos. Whether the stacks in Chicago Electric machines are a variation of the above Standard Player Action, or not, is conjecture at this point, but the pouch, horizontal valve, and deck mounted pneumatic layout shown above is close enough to be useful in understand the construction of stacks in most Chicago Electric instruments.

At far left is the pouch board, which also acts both as a front cover and vacuum header for the chest's individual horizontally oriented valves. Each pouch is connected to the appropriate tracker bar and inflates when a hole in the music roll admits atmospheric air pressure into the pouch. The inflated pouch pushes against a valve stem that in tern connects a piano pneumatic to the vacuum source while closing off the atmospheric vent side of the valve. The piano action is represented by the end of a piano action wippen, with a long wooden sticker extending downward (to a piano key omitted from the drawing). The player action pushes up on the felted extension of the wippen, in this case using what the Standard Pneumatic Player Action Company called a "flexible finger."

(Photograph courtesy of Dana Johnson.)

Working side of the front pouch board in Chicago Electric #191446 Model EL-2 keyboard style piano. Here the pouches for the treble end of the front pouch board are visible for what is obviously a two tier stack—i.e., two rows of pouches equals two rows of valves and in turn two deck boards holding the two rows of piano pneumatics. The rubber tubing, which is connected to brass nipples coming out of the bottom of the pouch board, go to the tracker bar. Between the nipples and the pouch itself is the bleed, which consist of a dished brass punching that is pushed into a hole drilled into the air channel for each pouch. At the center of the bleed punching is a tiny orifice that is just large enough to quickly draw air out of the pouch chamber once the music roll closes off a tracker bar opening, but that is also quite small in comparison to the much larger size of the opening in in the tracker bar.

(Photograph courtesy of Dana Johnson.)

Horizontally oriented valves in the chest for Chicago Electric #191446 Model EL-2 keyboard style piano. This view is of the front side when looking at and/or into the piano, but with the front cover/pouch board removed. The wood buttons on each valve stem are what the pouch pushes against to operate the valve. The size of the button is larger in diameter than is the valve seat itself, so as to be able to overcome the force of atmospheric air pressure holding the vacuum side of the valve seated and closed. This is obviously a two tier chest or stack, with a mating deck board for the piano pneumatics that are mounted to the chest directly behind the valve board. The red fiber valve stem guides and metal valve plates look similar in design to that of a Standard Player Action, but are enough different to cause doubt as to the true manufacturer of the stack assembly.

(Photograph courtesy of Dana Johnson.)

This view shows the left hand portion of the stack and the "tone modulator" (loudness control) in Chicago Electric #191446 Model EL-2 keyboard style piano. The front cover/pouch board has been removed. At the far left of the valve chest is a wooden slider valve (or regulator valve) that controls the vacuum level in the stack, which in turn modifies the volume of the piano. The rod attached to the slider extends upward through a close fitting felt bushing and on upward to a wood block attached to the movable end of the large regulator pneumatic. The movable leaf of this pneumatic is attached to a spring for which the tension can be adjusted; the more spring tension the louder the music. At rest the slider valve is fully up and open. When a vacuum builds within the chest the regulator pneumatic, which is connected to the vacuum supply within the chest, begins to collapse—until it reaches a point of equilibrium between the spring tension and the chest's vacuum level. The regulating action is fairly simple. As the regulator pneumatic collapses it moves the slider valve down against increasing spring tension, while simultaneously moving the slider down to increasingly restrict the flow of air out of the chest. As the air flow is increasingly restricted the vacuum level decreases until a balance point is reached between the spring tension pulling the regulator pneumatic up and the vacuum level trying to pull it down.

(Cusick Collection; photo courtesy of Art Reblitz.)

This bottom view of the pneumatic stack in a Chicago Electric Casino piano with xylophone shows that the piano pneumatics have wooden fingers and are glued to deck boards. The stack has two tiers of pneumatics, with simple wire push-rods passing through a guide rail under the poppets that play the piano action. This is clear evidence that the stacks in Chicago Electric cabinet style pianos were neither the Standard Player Action brand (which had metal fingers on the pneumatics and flanged fingers that played the piano action—see top illustration above), nor a Simplex Player Action, which had unit pneumatics with metal fingers. Although not confirmed, it is looking more like the stacks in the Chicago Electric upright coin pianos and the cabinet style pianos may have been made by the same manufacturer.