The_Mayflower_10_Plymouth_7029_valve_gear Close up of a Castle Class valve gear. The four-cylinder locomotive employs Walschaerts valve gear between the frames, controlling the two inside valves and cylinders, with rocking arms operating the valves of the outside cylinders. The rocking arms are observed passing through a port in the frame, at top, with another port below through which can be seen the slide bars of an inside cylinder. Such a layout, while perhaps aesthetically pleasing, does not make it easy for the locomotive crew to access the inside cylinders and valve gear for inspection and lubrication purposes. roger.griffiths@hotmail.com