Steam whistle
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- For the "Steam Whistle" beer brand, see Steam Whistle Brewing
A steam whistle is a device used to produce sound with the aid of live steam.
The whistle consists of the following main parts, as seen on the drawing: the whistle bell (1), the steam orifice (2) and the valve (9).
When the lever (10) is pulled, the valve opens and lets the steam escape through the orifice. The steam will alternately compress and rarefy in the bell, creating the sound. The pitch, or tone, is dependent on the length of the bell.
[edit] Uses of steam whistles
Steam whistles were often used in factories, and similar places to signal the start or end of a shift, etc. Railway locomotives, traction engines, and steam ships have traditionally been fitted with a whistle for warning and communication purposes.
Train whistles originated around 1832 by way of a musical instrument designer who made them for signalling purposes. On US locomotives they typically consist of three, four, or five whistles that sound together, usually forming a minor seventh chord. In the UK, locomotives were usually fitted with only one or two whistles, the latter having different tones and being controlled individually to allow more complex signalling.
Steam whistles for use on locomotives have since been replaced by air horns.
An array of steam whistles arranged to play music is referred to as a calliope.
Recent developments to the steam whistle include toroidal whistles, which behave as large virtual phased arrays of about 30 traditional steam whistles within a single toroidal chamber. This arrangement insures that the entire virtual array radiates in phase and adds to the output. Toroidal whistles are represented by the following patents:
U.S. Patent 4429656, Feb 7, 1984 Toroidal Shaped Closed Chamber Whistle
U.S. Patent 4686928, Aug 18, 1987 Toroidal Whistle
These whistles achieve outputs as high as 125-135 dB at 30 meters at a pressure of only 15 PSIG, making them comparable in both efficiency and output to the loudest warning sirens.
