As built the locomotives had
slide valves, but 20 were fitted with
piston valves and
superheaters between 1914 and 1920. The cylinder bore was increased by half an inch at the same time. In the infobox (right) 'ns' denotes non-superheated and 'su' denotes superheated. Some locomotives later had their superheaters removed but the piston valves were retained. ==British Railways==