In 1803 Richard Trevithick was employed by Samuel Homfray, the owner of the Penydarren Ironworks in Merthyr Tydfil. Trevithick was asked to produce a locomotive to be used to transport iron from Penydarren to the nearest canal. By February 1804 the Penydarren locomotive was ready for its first trip. On the 21st February it managed to haul ten tons of iron, seventy passengers and five wagons from the ironworks at Penydarren to the Merthyr-Cardiff Canal. During the nine mile journey the Penydarren locomotive reached speeds of nearly five miles an hour.
The Penydarren locomotive, with its single vertical cylinder, 8 foot flywheel and long piston-rod, became the first steam engine to run successfully on rails. Trevithick's locomotive employed the very important principle of turning the exhaust steam up the chimney, so producing a draft which drew the hot gases from the fire more powerfully through the boiler.
Trevithick's Penydarren locomotive only made three journeys. Each time the seven-ton steam engine broke the cast iron rails. Samuel Homfray came to the conclusion that Trevithick's invention was unlikely to reduce his transport costs and so he decided to abandon the project.
Yesterday we proceeded on our journey with the engine. We performed the nine miles in four hours and five minutes. We had to remove some large rocks on the way. On our return home one of the small bolts that fastened the axle to the boiler broke, and all the water ran out of the boiler.
We have tried the carriage with twenty-five tons of iron, and found we were more than a match for that weight. The steam is delivered into the chimney above the damper. It makes the draught much stronger by going up the chimney.
My father was at Penydarren when the engine was made and tried. Samuel Homfray, proprietor of the Penydarren Iron Works, Merthyr Tydfil, made a bet of 1,000 guineas with Richard Crawshay, of the Cyfarthfa Iron Works, that Trevithick's steam-engine could convey a load of iron from his works to the Navigation House (nine miles distant).
I assisted Mr. Trevithick in the making of his locomotive. She worked very well; but frequently her weight broke the tram-plates. On the third journey she broke a great many of the tram-plates. She was brought back to Penydarren by horses. The engine was never used as a locomotive after this.