(Ger. Ventil). In brass wind instruments, a device for diverting the air current from the main tube into an additional side tube. This lengthens the AIR COLUMN and therefore lowers the PITCH of the instrument's entire SCALE.

The valve system came into use about 1815. Before that time, trumpets, horns, and other brass could play only NATURAL (HARMONIC) tones above a single FUNDAMENTAL. In the orchestral scores of classical works, the parts of trumpets and horns, commonly set in a variety of pitches, compelled the player either to use several instruments in different KEYS or to manually insert extra tubing (CROOK) to change the length of the air column. Modern instruments eliminate this laborious procedure with the aid of three or more valves. As a result, a full CHROMATIC scale can be played. Valves may be operated with piston or rotary mechanisms.