Caerphilly Railway Works in Caerphilly, Glamorgan was the only main railway works in Wales
1899 built for the Rhymney Railway
Much of its initial work was in refurbishing older locomotives with new boilers and covered cabs.
1906 C. H. Riches who had been at Gorton railway works became Locomotive Superintendent and appointed J. H. Sellars as Works Foreman. Their policy was to modernise and standardise the locomotive stock, and Riches designed a standard boiler and cylinders for all the railway's tank engines.
He also designed a new class of 0-6-2 tank engine to be built by Robert Stephenson & Company who had provided six of their own design in 1903.
1919 Sellars became the Works Manager.
Until 1922 the works only repaired its own locomotives but this year engines started to be sent from the Barry Railway
At the time of the grouping of the railways the works were brought up-to-date to deal with tank engines working in the South Wales area. The development of Caerphilly works made possible the closing of other works in the area and the transference of the men to Caerphilly, thus centralizing locomotive repair, storage of spares, etc.
1923 taken over by the Great Western Railway at amalgamation.
1924 the first Swindon-built locomotive arrived
The works was enlarged with a new erecting shop in 1926.
The works also maintained a variety of wagons and passenger vehicles, building new mineral wagons and a few carriages, with a new workshop in 1901. However a new wagon works was built at Cardiff and, with work finishing its main work of converting Westinghouse air brakes to GWR vacuum brakes, the carriage and wagon works was phased out.
1932 Carriage and wagon repairs, which had been carried on at Caerphilly prior to the grouping, were discontinued and the work transferred to other depots in the district
1938 A new carriage lifting and painting shop was built alongside the old carriage shops.
1939 new workshops were built for carriage repairs only.
Until 1952 only tank engines had been repaired, but the efficiency of the works was such that they were asked to handle the smaller two-cylinder tender engines. They were so successful that larger engines were sent, the first being the 4-6-0 Number 5955 Garth Hall.
Around 1958 Swindon Works were committed to diesel locomotives and Caerphilly was sent Castle class and BR Standard locomotives.
With the withdrawal of steam on British Railways, the works closed in 1963 and the site converted into an industrial estate.
Sources of Information
-  Wikipedia