As built it would have been a well tank loco featuring Kitson's patent valve gear, which is prominent in this and in album photos. Originally it was hidden behind a plate, making the loco look like a side tank loco. The Great Western took control of the Cardiff Railway in 1923 and subsequently rebuilt the loco as a saddle tank design, revealing the valve gear and 'Westernising' the loco. The safety valves on top of the dome are an example of this. Notice the bell ahead of the cab, necessary in the confined spaces of the Cardiff dockland.