15 - Compound 230-4001 locomotive. Numbering and wheels

The first of the locomotives located beyond the roof of the Rotonda (Roundhouse) is German, built in 1901, and is called the “Compound” 230-4001. The MZA company purchased the “Compound” locomotives to modernise and extend its fleet; they were the first high-power ones to reach speeds of 100 km/h in Spain. It pulled fast trains between Barcelona and Madrid and on other routes of the main network. Its name comes from the technological system that was invented by the engineer Anatole Mallet, to use the excess steam coming out of the engine’s cylinders. Instead of this steam being expelled into the atmosphere, as was the case until then, the “Compound” system directed it into low-pressure cylinders in order to move other engine components.

What do the locomotives’ numbers stand for? The nationalisation of railways throughout Europe, and the establishment of Renfe in 1941, made it necessary to merge all the private wide-gauge companies into a single enterprise. In order to unify the names of all the existing locomotives, which had been peculiar to each company, the French method of two groups of figures was chosen. The first three-figure number designated, respectively, the number of leading, powered and trailing axles. In the second four-figure group, the first digit indicated the number of cylinders, while the other figures were a correlative number indicating the order within the series.

Therefore, the number of this “Compound locomotive” (230-4001) tells us that it has 2 leading unpowered axles, 3 powered axles connected by rods and no free trailing axles. Moreover, its engine had 4 cylinders and is the first in its series. By observing its system of wheels, we can recognise these technical characteristics.