History
The four principal ironworks at Merthyr Tydfil were Dowlais (built 1759), Plymouth (built 1763),Construction
The line was a single track plateway with a gauge of 4 ft 4 in over the flanges of the L shaped cast iron plate rails (or between the inside of the flanges). The plates were 3 ft long weighing 56 lb each and were spiked to rough stone blocks about 18 in square. There were frequent passing loops, at Plymouth Ironworks the line ran through a tunnel only 8 ft high beneath the charging area of the blast furnaces. The average gradient from Merthyr to Abercynon was 1 in 145. Near Quakers Yard two timber bridges carried the line over the River Taff where it runs through a gorge in a large loop. After the collapse of one of these bridges beneath a train in 1815 they were both replaced by brick arches. Later on chairs were introduced into which the plate rails were keyed.Operation
Initially one horse pulled about five trams, making one return journey a day. Later trains of about 25 trams hauled by 3 horses became normal. The owners of the line did allow other people to use it on payment of a toll but it is not known if anyone did. Regular locomotive working began in 1832.Rolling Stock
The wagons (or trams) were about 7 ft 6 in long by 4 ft 9 in wide at the top, made of wood strapped with iron and carried on cast iron wheels 2 ft 6 in to 2 ft 9 in diameter. They weighed about 15 cwt and carried at least two tons. There were 250 of them by 1830.Locomotives
Trevithick's locomotive built at Penydarren in 1804 made several runs after its famous initial run. On one occasion it was successfully tried hauling 25 tons. It weighed about 5 tons and broke many of the cast iron plate rails. In 1829 Stephenson supplied a six-wheeled locomotive with inclined cylinders mounted at the rear for use on the narrower gauge internal lines at Penydarren, it cost £375. In 1832 it was returned to Stephensons for conversion to a four-wheeled locomotive for use on the Merthyr Tramroad and at the same time the single flue was replaced by 82 copper fire tubes. It was at this time given the name "Eclipse" and commenced work on the Merthyr Tramroad on 22 June 1832. The chimney must have been hinged to allow it to go through the Plymouth tunnel. The Dowlais Company's line linking their works to the Merthyr Tramroad had a maximum gradient of 1 in 16.5 and considered too steep for locomotives to work by adhesion alone. In 1832 the Neath Abbey Ironworks supplied a six-wheeled rack and adhesion locomotive weighing 8 tons named "Perseverance" with inclined cylinders and twin chimneys (allowing them to be lowered alongside the boiler to pass through the tunnel at Plymouth). Another somewhat similar locomotive (but without a geared rack drive) named "Mountaineer" was built in 1833 by the Neath Abbey Co. for the Dowlais Company. As the drawings included a cross section of the Plymouth tunnel and it had a hinged chimney it was presumably intended to be used on the Merthyr Tramroad (unlike a second smaller locomotive built in 1832 which had a fixed chimney). The 0-6-0 "Dowlais" built by Neath Abbey in 1836 had the inclined cylinders mounted at the front (unlike the previous locomotives which had rear mounted cylinders) and rack drive for use on the incline to Dowlais. "Charles Jordan" delivered from Neath Abbey in 1838 was an adhesion only locomotive very similar to "Mountaineer". The last record of spare parts being supplied to Dowlais for these locomotives was in 1840-1841. An 1848 inventory of Dowlais plant lists only "Mountaineer" of the above locomotives. No plateway locomotives were listed in 1856. The locomotives had a maximum 3 ton axle load and plate layers were carried on the trains to replace broken plates. On 1 April 1839 more than 4,000 plates were required to make the tramway good though little more than half that number had been supplied by the three ironworks. By 22 June that year 1,600 more plates were broken, of which the Dowlais engines were blamed for smashing 1,450. By July the tramroad was reported to be almost impassable, for two days being blocked by a derailed Dowlais locomotive and Anthony Hill of Plymouth unsuccessfully applied to the Trustees for the locomotives to be banned.References
* {{refend Early Welsh railway companies Industrial railways in Wales Horse-drawn railways History of Merthyr Tydfil Richard Trevithick Transport in Rhondda Cynon Taf 4 ft 2 in gauge railways in Wales Railway lines opened in 1802