A Dictionary of Music and Musicians/Valve
VALVE (Fr. Piston; Germ. Ventil). A contrivance applied to brass instruments with cupped mouthpieces for increasing their powers of performance. It may be described as a second tube or bypath on one side of the main bore, into which the column of air may be diverted at will by a movement of the fingers; the original path being automatically restored on their removal. The side channels are obviously always longer than the simple passage, and therefore act by lengthening the tube, and lowering the note produced by a definite quantity. This quantity is approximately a tone for the first valve; a semi-tone for the second; a tone and a half for the third. Here the mechanism usually ends; but a fourth valve is often added, especially in baritone, bass, and contrabass instruments, which lowers the pitch about two tones and a-half. Cornets have indeed been made with as many as six valves, but they have not received general acceptation.
It is difficult to identify the original inventor of this ingenious contrivance. A rude form of valve may occasionally be seen on old Trombones, in which four parallel sliding tubes are actuated by a lever for each set, giving the instrument the appearance of a rank of organ pipes or of a Pandean reed. The earliest definite facts are two patents of John Shaw; the first taken out in 1824; the second, which he calls a 'rotary' or 'swivel' action, in 1838. The mechanism was much improved and simplified by Sax of Paris.
The two principal models now in use are the Piston and the Rotatory valve. The former is most used in this country and in France; the latter in Germany. The Rotatory valve is simply a 'fourway stopcock turning in a cylindrical case in the plane of the instrument, two of its four ways forming part of the main channel, the other two, on its rotating through a quadrant of the circle, admitting the air to the bypath.' This gives great freedom of execution, but is far more expensive and liable to derangement than the Piston valve. This, as its name implies, is a brass cylindrical piston moving airtight, vertically, in a long cylindrical case. It is pressed down by means of a short rod ending in a button for the finger at its upper end, and flies back to its original place under the influence of a helical spring acting on its lower extremity. On the sides of the case four passages abut; two from the main tube, two from the bypath. The valve itself is perforated obliquely by corresponding holes, which give the open note when it is at the top, the depressed note when it is at the bottom of its stroke. In the Rotatory valve these holes describe an arc of the circle; in the Piston they have a rectilinear vertical traverse.
Whichever form be used, it is intended to serve at least three purposes:
- To complete the scale.
- To transpose the key.
- To remedy false notes or imperfect intonation.
In four-valve instruments the first two of these requirements are combined, in order to bridge over the lung gap of an octave which exists between the fundamental note and its first upper partial: for example, the depression of pitch by 2½ tones places a B♭ instrument practically in the F below, and thus founds the whole scale on a new key-note, in which the three other valves produce fresh changes of interval.
The third requirement has been applied practically by Mr. Bassett to the trumpet, and his very valuable improvement is described under that heading. [Trumpet.]
The depressions and changes of pitch produced by each valve have been above named as approximate only. This fact constitutes the great objection to the system. For an instrument like the French Horn, which varies in length according to key from twelve to twenty-six feet, it is clear that a corresponding change must be made in the valve-slides, by which they remain aliquot parts of the main tube. This adjustment can be effected at the beginning of a composition by the player; but in sudden changes, either of crook, key, or of enharmonic nature, it is quite impracticable. In instruments, moreover, of large compass, like the Euphonium, the valve length is totally different according as the passage played lies in the lower or the higher register; still more so if the fourth valve has lowered the whole pitch of the instrument as above described.
In the French Horn, indeed, from the closeness of the harmonics to one another in the part of its scale chiefly used, two valves are sufficient, depressing the note a semitone and a tone respectively. A far better device for this instrument was, however, patented by the late Mr. Ford, and may be seen in the Patent Museum; but nowhere else, having been relegated, like so many other improvements, to the limbo of disuse. In this the piston arrangement, though working on the Rotatory method named above, actuates two short Trombone slides introduced into the main tube, and entirely does away with fixed bypaths. The player therefore has the power, as in the Trombone, of producing any note by ear, in correct intonation.
An equally ingenious if not quite so perfect a correction of the error inherent in this construction has been devised by Mr. Blaikley, of Messrs. Boosey's, under the name of Compensating Pistons, and is best given nearly in his own words.
In the ordinary arrangement the first valve lowers the pitch one tone; the second half a tone; and the third a tone and a half; but as the length of the instrument should be, speaking roughly, in inverse proportion to the number of vibrations of the required notes, the desired result is not exactly obtained when two or three valves are used in combination. Thus, in an instrument in the key of C, the first valve lowers the pitch to B♭, the third valve lowers it to A♭. For the low G the first valve is used in combination with the third, but its tubing is tuned to give the interval from C to B♭, and as the instrument when the third valve is down is virtually in A♮, the tubing of the first valve is not sufficiently long to flatten the pitch a true tone from A to G. This defect is intensified when all three valves are used together to produce D♭ and G♭. A numerical illustration may make this more clear: Let the first valve tubing be one-eighth the length of the instrument, and the third valve tubing one-fifth, the length of the instrument being unity; one-fifth added thereto will lengthen it in the right proportion to lower its pitch a minor third—i.e. from C to A♮. To produce G, we should be able to lower the instrument one tone from A♮, but the first valve will increase the length only one-eighth of unity, and not one-eighth (of 1+⅕). G will therefore be somewhat sharp.
Thus far with reference to instruments with three valves, but the defect is aggravated in those with four. Any actual lengthening of the valve slides by mechanism connected with the valve is practically inadmissible, as the lightness and rapidity of action of the valve would be thereby interfered with, but in the compensating pistons a lengthening of the valve slides is brought about as follows. The tubing connected with the third valve is passed through the first and second in such a way that when the third is pressed down, the vibrating column of air passes through passages in the first and second, in addition to the two passages in the third, as in the common arrangement; and for the purpose of bringing additional tubing into action in connection with the first and second valves, as required for correct intonation (when they are either or both used in combination with the third), two air passages are added to each of these valves, and in connection with each pair of passages a loop or circuit of tube of the required length, which is added to the effective length of the instrument only when the third valve is used in connection with the others. Such additional tubing compensates for the lowering of the pitch due to pressing down the third valve. No extra moving parts are introduced, and the established fingering is preserved.
[ W. H. S. ]