(Photograph courtesy of Dick Hack.)

Spill valve and balance-beam apparatus for a Simplex style expression control (from a junked out National piano). The large, stepped block of wood, in which the spill valve is located, is the left-side foot for a Simplex style stack. The stack itself sits atop the upper section with the bored holes, the larger hole being part of the vacuum distribution channeling for the stack. The dark colored wooden block attached to the left side of the foot is the rubber hose connector that is used to connect the stack foot with the vacuum pump. The three large wood screws loosely sticking up are used to secure the stack foot to the "keybed" area.

The metal seat for the spill valve fits into a circular recess that was then center-bored with a slightly smaller hole that connects with a vacuum channel in the stack foot. This metal valve seat is held securely in place by two small wood screws located in chiseled out notches on either side of the valve seat. This arrangement makes it possible to remove the valve seat to clean and/or repair the movable leathered valve body beneath it. Above the valve is the balance-beam, which pivots atop a cast bronze stanchion. Both ends of the balance-beam have been drilled with a loose fitting hole to accommodate an eyelet type threaded regulating screw, for which a pair of leather nuts on the threaded portion can be used to adjust the vertical position of whatever is attached to the eyelet. Such an eyelet screw is at the far end of the balance-beam, suspended directly over the spill valve, where its eyelet holds onto a stiff coiled extension type spring, for which the other end of the spring is connected to yet another but shorter threaded eyelet that is screwed into the spill valve body. By adjusting the tension on this extension spring the vacuum level of the player system can be likewise adjusted.

(Photograph courtesy of Dick Hack.)

Lock and cancel pneumatics for a Simplex style balance-beam expression control (from a junked out National piano). This interlocking pair of control pneumatics are mounted on the "keybed" area directly in front of the stack foot. The eyelet style threaded regulating screw, which is laying loose on top of the larger locking pneumatic, connects to one end of the balance-beam. When the larger pneumatic is activated (piano loud—tracker bar hole #71) it collapses, but only to the point whereby the metal latch blade (which protrudes past the top edge of the pneumatic) comes up against the felted bumper pad. Once contact occurs, the spring loaded metal hook snaps over the latch blade, keeping the locking pneumatic permanently held down, until the metal hook is pulled back by the smaller cancel pneumatic (piano soft—tracker bar hole #70), thereby releasing the larger locking pneumatic. The two brass elbows on the left side are the rubber tubing connections for the lock and cancel pneumatics, which are tubed to a pair of unit control valves on the stack.

(Photograph courtesy of Dick Hack.)

Left side stack foot (with vacuum level controls) for a Simplex style pneumatic stack (from a junked out National piano). This view shows the relative positioning between the stack foot and the lock and cancel pneumatics. It is the up or down position of the locking pneumatic (on the separate mounting board at left) that determines the relative position of the balance-beam, and, in turn, the amount of tension applied to the spill valve body. The higher the tension applied to the regulating spill valve, the higher the vacuum level in the player system (and the louder the piano notes will be played).

To adjust the soft piano expression level, start with the larger locking pneumatic in the unlocked upward or fully open position. Next adjust the spring tension on the spill valve so as to achieve a vacuum level sufficient to allow all stack valves to perform reliably, while still capable of quick repetition accuracy without any dropouts. The loud level, perhaps unfortunately, will be whatever comes about when the locking pneumatic is fully down and locked, and will depend upon the stiffness of the extension spring. If the loud setting seems too much or too little, consider replacing the extension spring with one that satisfies your personal preferences.

Keep in mind that National pianos do not have a vacuum reservoir to buffer and/or spill excess vacuum pump capacity. It is the vacuum expression control that deals with excess pump capacity, and so it is crucial that the spill valve work satisfactorily and be able to spill the full pump capacity during dead, non-playing moments, such as the beginning and end of a music roll. Otherwise the system vacuum level might rise to a level that could potentially damage certain parts of the vacuum pump.