Richard Trevithick: Merthyr Tramroad Trial

Note: This is a sub-section of Richard Trevithick

1804 February 21st. Merthyr Tramroad Trial. Samuel Homfray was so impressed with Trevithick's locomotive that he made a bet with another ironmaster, Richard Crawshay, for 500 guineas that Trevithick's steam locomotive could haul 10 tons of iron along the Merthyr Tramroad from Penydarren to Abercynon, a distance of 9.75 miles.

Amid great interest from the public it successfully carried 10 tons of iron, 5 wagons and 70 men the full distance in 4 hours and 5 minutes, an average speed of nearly 5 mph.

As well as Homfray, Crawshay and the passengers, other witnesses included Davies Gilbert and an engineer from the Government. The engineer from the Government was probably a safety inspector and particularly interested in the boiler's ability to withstand high steam pressures.

The locomotive itself was of a very primitive design. It comprised a boiler mounted upon a four wheel frame. At one end, a cylinder with very long stroke was mounted partly in the boiler, and a piston rod crosshead ran out along a slide-bar, an arrangement that looked like a giant trombone. As there was only one power stroke, this was coupled to a large flywheel mounted on one side. The rotational inertia of the flywheel would even out the movement that was transmitted to a central cog wheel that was, in turn connected to the driving wheels. It again used a high pressure cylinder without a condenser, the exhaust steam being used to assist the draught via the firebox, increasing efficiency even more. These fundamental improvements in steam engine designs by Trevithick did not change for the whole of the steam era. The bet was won.

It had been shown that, provided that the gradient was sufficiently shallow, it was possible to successfully haul heavy carriages along a "smooth" iron road using the adhesive weight alone of a suitably heavy and powerful steam locomotive. Trevithick's was probably the first to do so; however some of the short cast iron plates of the tram-road broke under the locomotive as they were intended only to support the lighter axle load of horse-drawn wagons and so the tram-road returned to horse power after the initial test run. Homfray was pleased enough. He had won his bet and the engine was placed on blocks and reverted to its original stationary job of driving the hammers.

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