Automatic Musical Company Stacks

(Photograph courtesy of Terry Barnes)

Overview of an Automatic Musical Company two-tier unit valve stack (Mandolin Piano, Haddorff #27096). The stack is mounted below the keybed and each individual unit valve actuates a vertical sticker that pushes up on the rear end of its respective piano key. The stack supporting framework is cast iron, with two horizontal wooden vacuum headers to which the individual unit valve assemblies are attached. Each unit valve is clamped in place by two long wood screws, one on each side, bearing on a shoulder along the side of the unit valve. Tracker bar tubing (which is not present in the photograph) connected each unit valve to the wooden tracker bar, which is to the upper right of the stack, but not visible in this picture.

(Photograph courtesy of Terry Barnes)

Close-up of the Automatic Mandolin Piano #27096 two-tier stack, showing the individual side-by-side unit valve assemblies. The rubber tubing to the tracker bar connects to the brass nipple extending out of the back side of the unit valve. One of the unit valve assemblies has been removed and is laying crosswise. At the front end is a small steel guide pin extending outward from the upper shellac-finished wooden base mounting block. This pin fits into a hole in the cast iron supporting frame to keep the front end of the long unit valve properly aligned and from flexing when a piano key is being pushed upwards. Looking at the lower tier header, the mounting area for the removed unit valve has a white leather gasket and the vacuum supply hole is fitted with a short brass nipple, so that the back end of the unit valve is properly aligned with the stack header.

(Photograph courtesy of Terry Barnes)

Close-up of a single unit valve assembly in Automatic Mandolin Piano #27096. At the left (or front end) is a steel pin that fits into a guide hole in the stack's cast iron framework. Below that is the wooden extension of the pneumatic (with a red felt punching) that the wire end of the sticker (that lifts the piano key) fits into. In the center is an oval shaped wood piece that serves both as the atmospheric vent and seal for the spacious valve chamber.

(Photograph courtesy of Terry Barnes)

Exploded view of a single unit valve in Automatic Mandolin Piano #27096. At the bottom is the motor pneumatic part that actuates the piano key, but its top stationary part is also drilled and milled to accommodate the pouch, bleed (to the right of the pouch) and tracker bar connection nipple.

At center is the main valve supporting structure. At the left is the guide pin that fits into the stack's cast iron framework. To the center is the valve chamber, with the vent passage to the pneumatic at its left and the valve seat to its right side. At the left side is the attachment area where the unit valve is clamped to the stack's vacuum header, with the hole being connected to a vacuum supply. Centered and above the valve chamber is the small button valve, with a leathered top side, that fits into the valve seat.

At the top is the oval shaped combination wood valve chamber seal and atmospheric valve vent. Flanking it (on both sides) are the long wood screws that serve to hold the valve block and adjoining pneumatic section together.

(Photograph courtesy of Terry Barnes)

Exploded top view of an early wood rocker-arm style unit valve assembly, which exemplifies a very different valve arrangement used by the Automatic Musical Company as per a Patent application filed on June 20, 1904, and renewed on July 5, 1906. Since this unit valve design was proposed in 1904 it is therefore presumed that it precedes the above pictured comparatively simple unit valves used in the Automatic Mandolin Piano of 1907. One thing that is known for certain is that this apparently formative design was made in at least two formats: One with flat metal rocker-levers as represented in the original patent drawing below, and the other being the later wooden rocker-lever type that is pictured just above.

In this style the atmospheric vent for the valve is at the front end of the assembly, as is the guide pin that fits into the stack's cast iron framework. The pouch that activates the rocker arm is underneath the right (or back) end of the rocker arm, and next to the pouch is a circular red fiber punching for the bleed. The valve itself is housed in the extruded metal pan, which is tacked to the wooden substrate and then sealed around the base of the metal pan and the two holes for the tacks.

(Photograph courtesy of Terry Barnes)

Exploded side view of the above early wood rocker-arm style unit valve. Only partially visible is a single coil torsion spring that is mostly hidden under the rocker-lever, which fits into a wire hook that holds the valve closed to the top of the extruded metal pan. When a vacuum is applied to the valve chamber and the tracker bar opening is sealed off the pouch is at rest, which keeps the motor pneumatic vented to atmospheric pressure. But when the tracker bar connection is open to atmospheric pressure the pouch inflates and the rocker arm overcomes the torsion spring and moves the valve so that it connects the motor pneumatic to the vacuum source while sealing off the atmospheric vent, thereby playing a piano note.

(Drawing from U.S. Patent 917,288)

Unit valve patent drawing (figure 11) from a Frederick R. Goolman Patent application #917,288 of June 20, 1904, renewed on July 5, 1906, and finally granted on April 6, 1909. This cross sectional view shows the unit valve in conjunction with related components. At left is the sticker that pushes up on the back side of a piano key. Above the unit valve assembly at its right side is the vacuum header to which the valve unit is attached by two wood screws. This drawing shows the rocking-lever as a flat metal strip that pivots under the head of a center nail. It is unknown what keeps the flat metal lever from swiveling out of alignment, but the design with the wooden rocking-lever pictured above resolves this potential problem with the standing center bushing that prevents any sideways swiveling motion.