Link Piano Company
Expression Controls
(Photograph courtesy of Rusty King) Early "Balance Beam" expression device: The "balance beam" and associated mechanical components are visible in the left half of the above picture. The beam (with a center pivot point) controls a spill valve connected on the right end of the beam. The vacuum level is maintained in accordance with the closing pressure exerted against the spill valve, which is maintained at a steady state by spring tension. By lowering the spring tension the vacuum level will correspondingly become less. The tension of the controlling spring is varied by means of a large motor pneumatic connected to the left end of the beam, with this pneumatic connected to a small control box visible on the right half of the above picture. |
(Photograph courtesy of Rusty King) Front view of a Link expression control box. The valve bleeds in the above example are located behind the black rubber buttons for easy cleanout. The tubing connections below each bleed are die stamped and from left to right the are: 4 (sustaining pedal), 2 (soft expression on), 1 (soft expression off - normal volume), 66 (coin trip - shut off). There is no atmospheric vent on the #2 valve (for soft expression on) and there is also a small nipple added to tee into the hammer rail pneumatic, so that the hammer rail is raised when soft expression is active. |
(Photograph courtesy of Rusty King) Top view of a Link expression control box. There are four individual valves in the unit, which are accessible by removing the smaller top wooden plate with the three screened holes that serve as atmospheric vents for each valves--except for the second valve from the left that has no external vent. The valves are, from left to right: Sustaining pedal; Soft expression on; Soft expression off (normal volume); and Coin trip--shut off. There is no atmospheric vent on the #2 valve (for soft expression on) and there is also a small nipple added to tee into the hammer rail pneumatic, so that the hammer rail is raised when soft expression is on. |
(Photograph courtesy of Rusty King) Late expression Device: The expression
apparatus described below is visible in the left half of the
above picture; its control box is in the right half. This
particular expression arrangement is thought to have been used
on all Link coin pianos about 1926 and later. The two soft
expression control pneumatics are at far left and under the
pump's vacuum header. The upper regulating pneumatic is spring
loaded and is connected to and regulates a choke valve in the
pump's vacuum header, so as to maintain a constant vacuum level.
The vacuum source for this pneumatic comes directly from the
stack, and it is held open by a spring attached to the soft
expression pneumatic just below it, with the soft expression
pneumatic held open by an even stronger spring. When the soft
expression perforation (tracker bar #2 hole) causes the hammer
rail to raise and the soft expression pneumatic to close it
eases up on the coil spring that holds the regulating pneumatic
open, thereby closing the choker valve a little and reducing the
vacuum level. |
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