Gradients are steep and curves are tight on the Welsh Highland Railway. Many locomotives do not have the power to cope. The Garretts built by Beyer Peacock in Manchester were powerful locos designed to operate over light track, sharp curves and harsh gradients of lines built to a tight budget. They soon became popular with loco crews.
The boiler is mounted on the “central frame”:https://en.wikipedia.org/wiki/File:Garratt_loco.png with two steam engines mounted on separate frames at each end of the boiler.
Articulation allowed the locomotives to negotiate curves and lighter rails that would have restricted large rigid-framed locomotives. The design aimed to double the power of the largest conventional locomotives, thus reducing the need for multiple locomotives and crews. The design proved so successful the locos were sold to railways across the world.
Three Garrett locos were bought from South African Railways in 1997 to work the line. These included No. 143 was the last Garratt built by the Manchester firm. Not only are these are some of the the most powerful steam locomotives ever built for 2′ gauge, they are also the largest 2’ gauge locos in the world.
For those wanting more “information.”:http://www.martynbane.co.uk/modernsteam/pg/ngg16a/ngg16s.htm
