Compound non-articulated locomotives enjoyed a brief heyday in the US around the turn of the last century. Baldwin's Sam Vauclain introduced the Vauclain Compound in the 1890's claiming an incerase in thermal efficiency of about 10 %. His system was followed by others including cross compounds, tandem compounds, balanced compounds and the afore mentioned three cylinder compounds. High maintenance costs and the chronic inability of the low pressure cylinders to do as much work as the high pressure cylinders negated some of the advantage of using steam twice. When super heating came along circa 1910 offering the same 10% advantage for a much cheaper price, compounding died out and surviving compound engines were converted to "simple" as quickly as possible.
The Rio Grande's 3-foot gauge K-27 class Mikados were originally built as Vauclain compounds. It was sort of a fad at the turn of the last century. Within a couple of deacdes or so, they were rebuilt as simple, because the cost of maintenance was too high and the low speeds on the narrowgauge couldn't take much advantage from compounding.
There were a number of other 4-cylinder compounds built for North America, but not a lot of success.
Three-cylinder locos enjoyed a similar fad among motive power buyers later in the 20th century. I get the impression these were generally more successful, but access to work on the third cylinder buried between the other two cylinders within the frame rails was a bit of a nightmare.
Mike Lehman
Urbana, IL
Don - non-Mallet type 3 or 4 cylinder compound engines were quite common in the erly 1900´s in Europe. Britain, France and Germany built a number of them for premium passenger service.
Just a few examples:
A friend of mind recently pointed me to a beautiful Swedish design engine.
What makes this interesting is it's a compound steam type with 4 cylinders, but only one set of drivers. From the picture I can only assume the high pressure drivers are on the inside driving a central crank attached to the driving wheel(s)
http://en.wikipedia.org/wiki/SJ_F_%28steam_locomotive%29
Don - Specializing in layout DC->DCC conversions
Modeling C&O transition era and steel industries There's Nothing Like Big Steam!