Duplexlok (Järnväg allmänt)
"Some of the more unusual steam locomotives had 'Duplex drive' where separate cylinders drove wheels or sets of wheels that were not all coupled together. This is otherwise known as 'divided drive'. Articulated locomotives have separate driving arrangements but are not considered to use duplex drive; a rigid wheelbase is required.
The usual motivation was to halve the stresses in the connecting rods that communicated the power of the cylinders to the driving wheels. In a conventional locomotive there is on each side one connecting rod driving one crank, and the other wheels are driven from that one by coupling rods. Clearly there is something of a bottleneck as on each side all the power of the engine has to go through one connecting rod and one crank-pin, and as US locomotives grew in size and power this was becoming a problem. Another issue is that the connecting rod has to be of massive construction and so is difficult to balance."