Steam whistle

A steam whistle is a device used to produce sound with the aid of live steam, which acts as a vibrating system (compare to train horn).

The whistle consists of the following main parts, as seen on the drawing: the whistle bell (1), the steam orifice or aperture (2), and the valve (9).

When the lever (10) is pulled (usually via a pull cord), 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; and also how far the operator has opened the valve. Some locomotive engineers invented their own style of whistling.

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. Large diameter steam whistles were used on light houses, likely beginning in the 1850s.

The earliest use of steam whistles was as boiler low-water alarms in the 18th century and early 19th century. During the 1830s, whistles were adopted by railroads and steamship companies.

Steam warning devices have been used on trains since 1833 when George Stephenson invented and patented a steam trumpet for use on the Leicester and Swannington Railway. Period literature makes a distinction between a steam trumpet and a steam whistle. A copy of the trumpet drawing signed May 1833 shows a device about eighteen inches high with an ever-widening trumpet shape with a six-inch diameter at its top or mouth. It is said that George Stephenson invented his trumpet after an accident on the Leicester and Swannington Railway where a train hit either a cart, or a herd of cows, on a level crossing and there were calls for a better way of giving a warning. Although no-one was injured, the accident was deemed serious enough to warrant Stephenson’s personal intervention. One account states that [driver] Weatherburn had `mouthblown his horn' at the crossing in an attempt to prevent the accident, but that no attention had been paid to this audible warning, perhaps because it had not been heard.

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