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Elements of Brass Instrument Construction: Disc Valves
Disc Valves ("Patent Lever Valves")
The disc valve is characterized by the use of two discs (c, d) facing each other, one fixed, the other rotating. The rotating disc either blocks the valve slide (left) or allows free passageway to it (right), hence increasing the overall tube length of the instrument.
Originally patented by John Shaw in 1838, an improved disc valve was subsequently introduced by John A. Köhler, who called it the "New Patent Lever Valve." However, the same principle was already known in France in 1835 as plaque tournantes or disques mobiles, where it was developed by the Parisian maker Halary.
In the photographs above, the left valve shows the fixed disc from the back, with cork stops. The right valve shows the rotating disc from the front, with bows, "finger," clock spring with tension-regulating disc, and lower part of push rod (disconnected from upper part and pointing downwards). The ring that normally surrounds this disc has been removed.
Disc Valve ("Patent Lever Valve") Diagrams