Modifications
Superheating of the boiler was first applied to no. 3702, Halifax in June 1910. All of the class had been fitted with superheaters by 1912. Boiler feed was originally by clack valves fitted to the underside of the barrel. Top feed was introduced in 1912 and new cast iron chimneys in 1921. The slide valves were replaced by 8 in (20.3 cm) semi-plug piston valves from 1914. All the engines were fitted with steam reversing gear but only a few, including no. 3716 City of London, had the gear replaced by the screw reverse. The Dean suspension bogie was replaced by a bogie developed from the type used on the de Glehn Atlantics.
Read more about this topic: GWR 3700 Class