valve

valvola (vil’-v6-la), I. 1. The device inv. by Claggett, 1790, and Bliihmel, 1813, by which natural bra instrs. are made chromatic. A natural horn produces the fundamental tone naturally made by a column of air of its exact length; it can be made to produce a series of partials of this tone by the method of blowing. Vide EMBOUCHURE and acoustics. The key of the horn can be changed by substituting for one section ot its tube a longer or shorter section called a crook, which alters the length of the horn, and the column of air, and alters therefore its fundamental key and gives it a new series of partials. Until the valve mechanism was invented a horn could therefore play only in one key at a time. Valve instrs. have auxiliary tubes fitted to the main tube; they are, in fact, merely stationary crooks. The pre ure of a certain valve acts as an instantaneous change of crook by shutting off the air in one crook and turning it into another of different length. This device permits the sounding of a complete chromatic scale along the instrument’s whole range. The valves are usually three in number, the first lowering the pitch a semitone, the second a tone, the third three semitones, thus giving a command of all keys (cf: HARP), (a) the piston, or piston-valve, is a plunger in an air-tight cylinder; by means of two holes the plunger at rest carries the air through the main tube; when pre ed it shuts off the main tube and opens a side-tube, thus changing the key; a spiral spring restores it after pre ure to the natural position. (b) the rotary valve is a stop-cock with four holes which produce the same effect. 2. organ valves are (a) suction-valves, or suckers, which admit the wind to the bellows and retain it there; (b) joint-valves which regulate the air density in the wind channels. (c) key-valves or pallets, which are worked by a draw-stop; and (d) the waste-pallet relieving the bellows of surplus air. v. a due valzer (vil-tsar), I. Waltz. pa i. Two-step.