The class were fitted with a steam chest and slide valves located beneath the cylinders. The valves were driven by Stephenson valve gear. This inverted arrangement of slide valves and steam chest, originally introduced by William Stroudley of the LB&SCR, allowed the valves to drop away from the cylinder's steam port faces when the regulator was closed, thus reducing wear. Because the steam chest was below the cylinders, and not between them, the latter could have an increased diameter. The centre line of the cylinders was inclined at an angle of 6° to the centre line of the valves, each centre line being aligned with the driving centre. This arrangement allowed the valve rods to be driven directly from the expansion link. First used on the Armstrong and 3031 Classes, this arrangement of cylinders, valves and valve gear was subsequently used on all GWR outside framed 4-4-0s, with the slide valves being eventually replaced by piston valves.