(Catalogue illustration courtesy of Dana Johnson.)

Catalogue illustration showing a hand holding a Simplex Pneumatic Action Unit. According to the catalogue text accompanying this illustration: "The Pneumatic Action for striking the notes of the Piano is built on the unit system, each individual note being a complete working unit in itself." The catalogue further states: "All of these units are interchangeable and easily removed from the instrument. As most of the work on these units is done on automatic machinery, they are made with a precision so necessary to insure uniformity of operation and durability of structure."

(Illustration from The Music Trade Review, 1914.)

A cross-section illustration of a Simplex Player Action stack with, for simplicity of explanation, only one combination valve/pneumatic unit attached. The stack's front cover (A) serves as both an vacuum header and access panel. With it removed the two wood screws (M) that attach each individual unit valve assembly can be easily removed and unit valve assembly exchanged for a new unit. At the top edge of the main vertically oriented manifold board (C)—located behind the cover board (A)—is the tracker bar tubing header (D) with brass nipples inserted into the pouch channel (K) that project out toward the rear of the stack. The rubber tubing for the tracker bar connects to these nipples. The pouch (I) with its bleed (L) operates against the controlling valve (H).

Referring to this illustration and the one immediately below, here is how the Simplex catalogue puts it: Chamber B is under vacuum tension whenever the pump is operational. When an opening in the paper music roll registers with the opening X in the tracker bar a pulse of air is drawn through the opening X into tube K and the leather disk in the pneumatic is raised by the air tension always on chamber B. This lifts the valve in the pneumatic, closing the port to the open air, and opening the part immediately below. This air tension collapses the movable leaf of the pneumatic and operates to strike the note in similar manner as raising the rear end of the piano key by depressing the front of the key by hand. The parts remain in that position as long as the opening continues in the paper. When that ends, the disk is pushed down to its former position by the weight and suction on the valve, and other parts return to their former position.

(Illustration from The Music Trade Review, 1914.)

This complete cross section view of a Simples Player Action stack clearly demonstrates the relationship between the spoolbox with its tracker bar ("X"), the actual piano stack situated below the spoolbox, and the piano action itself, which is represented here by the simple outline of a piano key at picture bottom, and at right the vertical sticker and a portion of a piano action wippen with its bridal strap and hammer back-check wires sticking upwards.

(Illustration from The Music Trade Review, 1917.)

This illustration taken from a Simplex Player Action Company advertisement printed in 1917 demonstrates the ease by which a unit valve assembly can be quickly removed and then replaced. Once the front cover, which doubles as a vacuum header, has been removed just two more easy to reach wood screws and the usual repair job is nearly done, This simplicity of construction and of any future maintenance is probably the foremost advantage of the Simplex stack, as well as the motive behind using the Simplex name.

(Catalogue illustration courtesy of Dana Johnson.)

A birds-eye view of the Simplex Player Action factory and office buildings in Worcester, Massachusetts. According to the catalogue this complex had the capacity of turning out 40,000 player actions per year. Most of this output found its way into 88-note player pianos, with only a relatively modest number installed in various coin pianos brands.