Steam spring

Steam springs or steam suspension are a form of suspension used for some early steam locomotives designed and built by George Stephenson. They were only briefly used and may have been used for fewer than ten locomotives.

Early railways used cast-iron fishbelly rails. These were brittle and prone to cracking under shock loads. The new steam locomotives of the 1820s were much heavier than the horse-drawn wagons of earlier plateways. Locomotives of this period also used vertical cylinders set within the boiler. The vertical forces of the moving pistons further gave rise to hammer blow, which increased the load on the rails.

A further reason for suspension was to improve the frictional contact between the wheels and rail. This relied upon maintaining a good contact, thus requiring good suspension of the wheels over the uneven track. The ability of an 'adhesion-hauled' locomotive to draw a train was much questioned at this time, as it was thought that the friction between a smooth iron wheel and the rail would be inadequate. Some designers, such as Blenkinsop with his Salamanca thought that a system of geared teeth would be necessary. Stephenson believed that, provided a good contact could be maintained between wheel and rail, frictional adhesion alone would be adequate.

At the time of these early locomotives there was not yet a way of forging an adequate steel spring to carry the weight of a locomotive. High quality steel had been available since Huntsman's crucible process, but it was still so expensive as to be regarded as 'a semi-precious metal'. It would be another forty years before Bessemer's converter made cheap bulk steel available. A similar problem affected safety valves, causing them to rely on dead weights or Hackworth's bulky stack of leaf springs, rather than the ubiquitous steel coil spring that would appear later.

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