The Semmering Railway, opened on 17 July 1854, was one of the first true mountain railways, traversing a section of the Austrian Alps. It was characterized by steep gradients and sharp curves. To work this railway a new design of locomotive was developed.
A competition was held to decide which locomotives would be bought for operation on the Semmering Railway. One stretch of the line had gradients of 1 in 40 (2.5%) and curves with a minimum radius of 190 metres (210 yd) and a maximum radius of 285 metres (312 yd). A speed of 11.5 kilometres per hour (7.1 mph) was required to be maintained and a maximum axle loading of 14 tonnes, with a boiler pressure not exceeding 8.5 kgf/cm² (830 kPa).
There were four entrants, Bavaria, built by Maffei; Wiener-Neustadt built by Wiener-Neustadt; Seraing built by Société anonyme John Cockerill in Belgium and Vindobona built by the Glognitz Bahn in Vienna. All four locomotives met the trial conditions, but none proved reliable in practical use. The Semmering Trials led to a number of developments in locomotive design: Fairlie's Patent of 1863, The Meyer locomotive and the Mallet locomotive.
The Engerth Design
The Engerth design articulated the tender with the main locomotive frame, allowing some of the weight of the fuel and water to be carried on the driving wheels to improve adhesion. Because the tender was articulated, rather than directly attached to the frame, the locomotive could traverse relatively sharp curves, while still enjoying the advantage of the additional adhesive weight gain. The original design also included an indirect drive from the main driving wheels to the wheels under the tender. This arrangement proved too complex to maintain and was dropped from the design.
Sixteen locomotives were supplied to the Semmering Railway between November 1853 and May 1854. They proved capable of 19 kilometres per hour (12 mph) uphill on gradients of 1 in 40 (2.5%).