A piston trombone is a type of trombone which uses piston valves to create notes rather than a slide. Although the piston trombone is technically only one of a number of different kinds of valve trombone, the terms are usually used interchangeably, with most references to a valve trombone referring to a piston trombone. This type of trombone is less common than the slide trombone, particularly in the English-speaking world, but it continues to exist worldwide.
In a slide trombone, the player moves a long metal slide back and forth, lengthening and shortening it. By doing so, the player increases and decreases the size of the air column inside the instrument, lowering and raising the pitch of the sound coming from it. By combining this with the position of the mouth, the player can produce a wide range of different notes.
Like the slide trombone, the piston trombone produces varying pitches by changing the size of the tube in the instrument. Unlike the slide trombone, the piston trombone changes the size of the tube not by physically extending or contracting it, but by using valves, called Perinet valves, to cut off the flow of air in parts of the trombone. The player depresses a key which pushes a piston down into the valve to activate it. The arrangement of valves resembles the valves of a trumpet. Piston trombones thus resemble traditional trombones, but without the movable slide and with a small bank of keys like those of a trumpet.
The piston trombone has some advantages and disadvantages compared to its slide counterpart. Some trombonists believe that piston valves make it easier to play fast passages, since depressing and releasing a valve takes much less time than moving the slide. Valve trombones therefore occur in some orchestral scores which require rapid sequences of short notes from the trombone. Valves are also easy to play while marching or mounted, which was an important factor for trombonists in military or civic bands. This type of band was common in the 19th century, the period of the piston trombone's introduction.
The slide trombone remains more popular in most orchestras than the valve or piston trombone. There are several reasons for this continued popularity. The characteristic smooth transitions of the slide trombone are much harder with a valve trombone, meaning that many pieces intended for trombone lose this effect when played on a valve trombone. Many trombonists prefer the tone of the slide trombone, which is said to be more open than that of the piston trombone.