Freight Train Steam Locomotive with a Tender.

After intensive experiments with the two class 42.90 Franco-Crosti locomotives, the German Federal Railroad decided to convert several class 50 locomotives in the same manner. A Franco Crosti boiler is a conventional locomotive tank with a second boiler connected in the steam lines. It heats feed water with the assistance of smoke exhaust gases passing over the water. This second boiler is therefore called an exhaust gas pre-heater. The Italian designers Franco and Crosti built their first test units with this technology as early as the Thirties. The savings in coal were approximately 20 % with the improved efficiency. The flat smokestack for operation projects from one side of the boiler, which results in a rather striking appearance. The standard smokestack no longer serves to discharge smoke exhaust gases during operation, but is only required for firing up the locomotive. Relatively high operating costs resulted despite the increased efficiency, since the pre-heater boiler was easily subject to corrosion. A total of 31 locomotives were delivered to the German Federal Railroad by Henschel in 1954 and 1958, and were designated as the class 50.40. These two-cylinder, 90.6 metric tons heavy locomotives had a maximum speed of 80 km/h / 50 mph in both directions and an indexed performance of 1,540 pounds per square inch. They were used in the Münsterland area and in the Rhine area in freight train service until they were retired in 1967 and then scrapped.