The Taff Vale Railway O4 class was a class of 0-6-2T steam tank locomotives designed by Tom Hurry Riches and introduced to the Taff Vale Railway in 1907. They were rebuilt with taper boilers and superheaters by the Great Western Railway (GWR) from 1924.

Taff Vale Railway O4 class
'O4' No. 289 at Danygraig Locomotive Depot, Swansea Docks 1946
Type and origin Power type Steam Designer Tom Hurry Riches Builder Beyer, Peacock & Co. (24); Manning Wardle (7); Vulcan Foundry (10) Build date 1907 (7), 1908 (14), 1910 (20) Total produced 41
Specifications Configuration: ​  • Whyte 0-6-2T Gauge 4 ft 8+1⁄2 in (1,435 mm) standard gauge Driver dia. 4 ft 6+1⁄2 in (1.384 m) Loco weight 61 long tons (68 short tons; 62 t) Fuel type Coal Boiler pressure 175 psi (1.21 MPa) Cylinders Two, inside Cylinder size 17.5 in × 26 in (444 mm × 660 mm)
Performance figures Tractive effort 21,730 lbf (96.7 kN)
Career Operators Taff Vale Railway Great Western Railway; British Railways Retired 1948–1955 Disposition All scrapped

The first loco withdrawn was 402 in April 1948 from Treherbert shed. The last three locos, 290, 317 and 321 were withdrawn together from Cardiff East Dock shed in July 1955. None were preserved.