Fairlie Locomotive - Single Fairlie or Mason Bogie

Single Fairlie or Mason Bogie

A variation of the Fairlie that enjoyed some popularity, especially in the United States, was the single Fairlie, essentially half a double Fairlie, with one boiler, a cab at one end, and a single articulated power bogie combined with an unpowered bogie under the cab, maintaining the ability to negotiate sharp turns. This design abandoned the bidirectional nature of the double Fairlie but gained back the ability to have a large bunker and water tank behind the cab, and the possibility of using a trailing tender if necessary. The single conventional boiler made maintenance cheaper and did away with the crew's separation. A fair number were built, especially by Fairlie's licensee in the United States, William Mason, who built 146 or so Mason Bogies. In the UK, a single Fairlie 0-4-4T was used by the Swindon, Marlborough and Andover Railway and three 0-6-4T by the North Wales Narrow Gauge Railways.

Interestingly, in both the UK and the USA, these single Fairlies were the first locomotives in each country to use the European Walschaerts valve gear. The Stephenson link gear, which was usual at the time, used multiple eccentrics between the frames but the Walschaerts gear was mounted outboard of the frames and connecting rods. This was advantageous because the Fairlie system required this space between the frames for the bogie pivot.