Franco-Crosti boiler

The Franco–Crosti boiler is a type of boiler used for steam locomotives. It was designed in the 1930s by Attilio Franco and Dr Piero Crosti.

The Franco–Crosti boiler is a modification of the conventional fire tube boiler design used on most steam locomotives. Unlike conventional boilers the heat remaining in the exhaust gases is used to preheat the water supply for the main boiler using a secondary heat exchange mechanism. This mechanism, known as the feedwater heater is essentially a secondary boiler. The preheated feedwater is fed at full boiler pressure into the main boiler via clack valves.

The feedwater heater is not designed to produce steam, instead raising the temperature of the feedwater. This allows the heater to utilize the remaining energy in the exhaust gases effectively.

The typical configuration of a Franco–Crosti boiler had a relatively conventional main boiler with one or two secondary feedwater heaters running parallel to the boiler barrel. Where the loading gauge did not allow the feedwater heater to be placed beside the boiler it was mounted beneath.

When the locomotive is started, cold water is fed directly into the main boiler which operates normally with the exhaust gases flowing out of the main chimney via the smokebox. Once the boiler is producing steam, the exit from the smokebox into the main chimney is closed and the exhaust gases instead flow through the feedwater heater and exit via the secondary chimney located towards the rear of the locomotive. Water fed into the boiler is now pre-heated in the feedwater heater and enters the boiler at higher than normal temperature.

The first Franco-Crosti boilered locomotive was built for the Belgian State Railways as No. 2096 in 1932. This massive 0–6–2 + 2–4–2–4–2 + 2–6–0 locomotive weighed 248 tons and developed around 3,000 horsepower. It was essentially two Franco-Crosti boilered locomotives joined back-to-back and was one of the most powerful articulated locomotives ever built.

During the German occupation of Belgium in the Second World War the locomotive was separated into two 0–6–2+2–6–2T locomotives. These locomotives were captured by invading Russian troops in 1945 and at least one of them was still in service in Poland in 1955.

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Wikipedia