On a brass instrument, a valve is a mechanism that, when in use, directs the air column along additional tubing inside the instrument, thus producing a different fundamental and harmonic series.Most modern valved instruments employ similar valve systems which results in the same patterns of valve combinations to alter a pitch. For example, depressing the first valve will normally result in lowering the original pitch by one step, or the interval of a second. The table below shows the valve combinations of a typical valved instrument and the resulting pitch alterations. It should be noted that the addition of the fourth valve became common in the mid-20th century to help produce better intonation with the third valve combinations that tended to be "out of tune" or having poor intonation (especially the 1st & 3rd valve combination). Valves can be created in a rotary or piston configuration.See also rotary valve, piston valve.Valve CombinationsPitch Lowered2nd Valve1/2 step1st Valve1 full step3rd Valve1 & 1/2 steps1st & 2nd Valves1 & 1/2 steps2nd & 3rd Valves2 full steps1st & 3rd Valves2 & 1/2 steps1st, 2nd, & 3rd Valves3 full steps4th Valve Combinations'4th Valve2 & 1/2 steps2nd, & 4th Valves3 full steps1st, & 4th Valves3 & 1/2 steps3rd, & 4th Valves4 full steps1st, 2nd,, & 4th Valves4 full steps2nd, 3rd, & 4th Valves4 & 1/2 steps1st, 3rd, & 4th Valves5 full steps1st, 2nd, 3rd, & 4th Valves5 & 1/2 stepsAnimation of the trumpet valves.device for diverting the air flow in a brass instrument away from a section of the main tube and into a tube of a different length, giving a different pitch<br><br>A mechanical device for adding, virtually instantaneously, a fixed length of tubing into the windway of an instrument. Most valves are `descending valves' which add to the air column length when operated; with the rarer `ascending valve' the air column is longer when the valve is not operated