Württemberg Hz

The Reutlingen-Schelklingen railway line had a section between Honau and Lichtenstein, on whose ten percent incline the Fz class rack locomotives previously used were soon no longer sufficient. Therefore, the Württemberg State Railways ordered the new type Hz from Maschinenfabrik Esslingen, which was ten-coupled and was taken over directly by the Reichsbahn after it was founded.

The Hz shared some of its parts with the Tn and T 5 locomotives. The main difference was the Winterthur-type rack system, which was driven by two additional cylinders. Before entering the rack, the rack wheel had to be brought up to speed. To do this, the upper cylinders were briefly powered by live steam before switching to compound mode. From this point on, the lower cylinders powering the wheels served as high-pressure cylinders, the exhaust steam from which flowed into the upper cylinders of the rack drive, which now acted as low-pressure cylinders.

After the first expansion, the steam had a larger volume, which was opposed by all cylinders having the same dimensions. This was compensated by the fact that the upper gear wheel rotated at twice the speed and the power transmission to the actual gear wheel for the rack took place only through a reduction gear.

In the years 1922 and 1925, four locomotives were completed, which were put into service by the Reichsbahn as class 97⁵. They all survived the war and were then taken over by the Bundesbahn. From 1952, two received a modernization, whereby they received a new steel firebox, a reinforced frame, centering springs on the laterally adjustable end axles to improve running smoothness and an increase in the coal bunker by one tonne. The first locomotive was retired in 1956 and the rest in 1962 after rack railbuses were introduced. Three of them are still preserved today.