Canada Science and Technology Museum

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A Closer Look

A Sampler of
Scientific Instruments

CN Gallery

Guide to Donating or
Selling Objects

How is the Shay Different?

How is the Shay Different?

A typical steam locomotive transmits power from the boiler to its cylinders. These cylinders are on either side of the boiler and make up the steam engine that powers the driving wheels using a system of interconnected rods and cranks. This system, as applied to a railway locomotive, was initially developed in 1804 in Great Britain by Richard Trevithick. It was substantially improved in the system used by George Stephenson on his small 1829 locomotive, Rocket, the prototype for most future steam locomotives.

The system of horizontal driving rods and the long rigid wheelbase typical of more traditional mainline steam locomotives is clearly visible on Canadian Pacific 2858 (670006*). (CSTM)

In the typical steam locomotive, there are two groups of rods, each connected to one or more cylinders located on either side of the locomotive. These rods convert the pistons’ reciprocating (back and forth) motion into the driving wheels’ rotary motion. Because the tractive effort (pulling capacity) of the locomotive is partly dependent on the number and diameter of driving wheels, engines with high tractive effort tend to have many connected driving wheels, making the wheelbase comparatively long and rigid. For example, some of the largest steam locomotives in Canada had rigid driving wheelbases of 22 feet (6.7 metres). Moreover, the majority of steam engines haul their fuel and water in separate tenders behind the engine. The tenders contribute to the overall length of a steam locomotive and to the dead weight the locomotives have to pull.

This type of locomotive design is suited for large public railways where hauling capacity, range and speed are important. Stable tracks are required to allow conventional steam locomotives to haul heavy loads quickly. To meet stability requirements, grades seldom exceed three percent (a rise of 3 metres over 100 metres) and the tracks are constructed with long gentle curves. Moreover, since the tracks are permanent, railway companies invest considerable sums of money in their construction and maintenance.

* The numbers in brackets are the accession numbers of artifacts held by the Museum.