Water key

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A water key is a valve or tap used to allow the drainage of accumulated fluid, consisting of condensed breath moisture, from musical instruments such as trombones or trumpets. It is otherwise known as a water valve or, less euphemistically, a spit valve. In valved instruments, they are found always on the main tuning slide, and sometimes on valve slides. On the trombone, it is on the downwind side of the bend in the hand slide. Baritone saxophones have a water key at the bottom of the loop at the top of the instrument.

They are often erroneously referred to as "spit valves", as the myth persists that some or much of the liquid consists of spit. It doesn't. The amount of water accumulated is directly in proportion to the size of the instrument, and the amount of metal exposed to the air, which in turn enables the process of condensation due warm, moist air from the lungs meeting metal cooled by room-temperature air.


Water keys are of two types.

The older, traditional design features a simple lever key as found on woodwinds, but with a cork rather than a pad in the cup. A spring holds the cork against a raised hollow cylinder mounted on the slide or loop during play. To drain, the player presses the non-cup end of the key towards the instrument to open the valve.

The other design is called an Amado water key after its inventor. It consists of a short hollow cylinder mounted transversely on the slide. The cylinder has a button on one side that operates an enclosed stopper valve held shut with a spring, and a hole on the bottom side to drain the water. The player presses the button and blows into the horn to drain the water. The Amado design has the advantage that it presents less of a deviation from a smooth inner slide wall that the larger-volume drain port in the traditional design. Nevertheless, most modern horns are still fitted with the traditional design of water key.

Anatomy of a trombone (part 5 is the water key)