valve

valve, in music, a device, first used in 1815 by musicians Heinrich Stölzel and Friedrich Blühmel of Berlin, that alters the length of the vibrating air column in brass wind instruments by allowing air to pass through a small piece of metal tubing, or crook, permanently attached to the instrument. Descending valves switch in extra tubing, lowering the fundamental pitch; the less common ascending valves cut air off from the tubing, raising the pitch. Valves enable players to produce notes lying outside the harmonic series of an air column the length of the original tubing (in relative pitch, C–c–g–c′–e′–g′–b♭′ [approximately]–c″–d″–e″, etc).

Brass instruments normally have three descending valves; used in combination they can lower the pitch of the instrument six semitones. Two principal switching methods are used: piston and rotary mechanisms.