History
The Walschaerts valve gear was slow to gain popularity. The Stephenson valve gear remained the most commonly used valve gear on 19th-century locomotives. However, the Walschaerts valve gear had the advantage that it could be mounted entirely on the outside of the locomotives, leaving the space between the frames clear; which resulted in it being adopted in some articulated locomotives.
In 1874, New Zealand Railways ordered two types of Double Fairlie locomotives from Avonside. Both the B class and E class Double Fairlies were fitted with Walschaerts valve gear. This was certainly the first use of this technology to be used in New Zealand, and is possibly the first time a British manufacturer had supplied it.
The Mason Bogie locomotive type was the first to use the Walschaerts gear in North America.
The first application in Britain was on a Single Fairlie 0-4-4T, exhibited in Paris in 1878 and purchased by the Swindon, Marlborough and Andover Railway in 1883. According to Ahrons, the locomotive saw very little service as nobody seems to have known how to set the valves and this led to enormous coal consumption.
In the 20th century, the Walschaerts valve gear was the most commonly used type, especially on larger locomotives. In Europe, its use was almost universal, whilst in North America, the Walschaerts gear outnumbered its closest competitor, the Baker valve gear, by a wide margin.
In Germany and some neighbouring countries, like Poland and Czechoslovakia, the Walschaerts gear is often named the Heusinger valve gear after Edmund Heusinger von Waldegg, who invented the mechanism independently in 1849. Heusinger's gear was closer to the form generally adopted, but most authorities accept Walschaerts' invention as sufficiently close to the final form.
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