Articulation
Mallet found typical main line railways unwilling to adopt his particular ideas and, in 1884, he started to propose compounding combined with articulation; on lightly engineered secondary lines this could give greater power to locomotives whose axle load and size was limited. His patent 162876 in France specified four cylinders, two large and two small, with one pair of cylinders acting on two or three fixed axles, and the other pair acting on axles mounted in a swivelling truck
Diagrams provided by Mallet make it clear that the swivelling truck was to be a Bissell truck, that is, a pony truck or bogie pivoting about a vertical pin some distance behind the centre of the truck itself. The weight of the front part of the locomotive frame was to be supported on an arc shaped radial bearing. The truck could therefore turn into a curve and move to some extent laterally.
Mallet considered that the major advantage of this arrangement was that it enabled the cylinders on the truck to be fed with low pressure steam: the high pressure cylinders were on the fixed main frame and only low pressure steam needed to be carried to the low pressure cylinders.
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