Prussian P 4¹

The Prussian State Railways designated passenger locomotives with a 4-4-0 wheel arrangement as P 4¹, which were originally delivered in the 1990s with simple steam expansion and saturated steam technology. These were two slightly different variants, which were referred to as “Erfurt type” and “Hanover type”.

The Erfurt type came from a series of eight locomotives that had been built to compare different designs. Two locomotives each were built with compound and simple engines and with different driving wheel diameters. The P 4¹ emerged from the variants with a diameter of 1,730 mm, while the two specimens with a diameter of 1,960 mm were designated the S 3. The P 4¹ went into series production with a simple engine, so that between 1891 and 1893, including the two test locomotives, a total of 57 units were built. The main reason for the early cessation of series production was the front bogie, which had often caused problems.

The Hanover design was thus a further development, with the bogie being redesigned in particular. In addition, the diameter of the cylinders had been increased by 30 mm to increase power. The valve gear linkage had been moved from the inside to the outside. Due to a different distribution of the loads, the newer design had more load on the driven axles despite a lower total weight. With a maximum speed of 90 km/h, they were also used in front of express trains, especially at the beginning, but later more and more powerful machines took over this task. By 1902 a total of 428 machines had been completed.

Both types have been modified over time. Since the pre-production locomotives of the Erfurt type included two with a compound engine, more of the series locomotives were later converted in this way. A Hanover-type example was fitted with a flame tube superheater shortly before the turn of the century, making it the second superheated steam locomotive after an S 3. These attempts were made under the direction of Robert Garbe, the head of the Prussian State Railways' design department, and ensured that soon outside of Prussia almost exclusively steam locomotives with superheated engines were being developed.

When it was taken over by the Reichsbahn, a total of four of the older design were still planned for the renumbering plan. In fact, only one of the locomotives with a compound engine was renumbered in 1925, which was given the number 36 001. A total of 157 locomotives of the Hanover type were counted in 1923 and the numbers between 36 7001 and 36 7202 were reserved for them. In the two years until the actual renumbering, almost all of them were taken out of service, so that finally only nine machines were taken over.