P3 1609, Graffenstaden 1894.
P3 Graffenstaden

This machine corresponds to the first style ' alsacien' before De Glehn. The Compound process was already of everyday usage on the fixed steam machines of the navy since the years 1860. But should be waited until 1874, with the patent deposited by Anatole Mallet, to extend this technique to the railway engines. The increase in the pressure of the boilers comprises an economic advantage in thermal terms of units and increases the work provided by the vapor in the cylinder. But the fall of temperature, between the admission of the hotter vapor and its exhaust, is much more significant. It results from it a cooling from the walls and a vapor loss in the form of condensation considerable. The solution is thus to subdivide the process of relaxation on several cylinders: it is the principle developed on the engine compound. De Glehn, in collaboration with De Bousquet, proposes then a type 220 with engine compound with four cylinders and mechanism independent for the network of the NORD. This numbered machine 701, although still comprising defects of youth, is at the origin of re-elected Alsatian School.