Design Features
The design initially caused major difficulties, because it had to keep to the maximum permitted axle load for the railway network of 16 t (15.7 long tons; 17.6 short tons).
This limitation led to the weight savings in many areas. At first, the plate frame was made of 22 mm (0.87 in) thick material; this later had to be changed to the usual 25 mm (0.98 in). On the first few engines, a smokebox superheater was installed, but the design this was changed during the first year in favour of a Schmidt smoke tube superheater. The long boiler was located well forward in order to spread the weight to the front carrying wheels and to keep the axle load within the maximum limits, thus giving the engine the typical appearance of a "Garbe locomotive".
The driving wheels of the S6 had the rather unusual diameter of 2,100 mm (82.68 in) in order to keep the rpm down and to guarantee the smooth running of the driving gear. Originally a diameter of 2,200 mm (86.61 in) had been planned, but in the end it was reduced by 100 mm (3.94 in). The heavy balancing masses of the driving gear were badly affected by weight savings. That resulted in serious jerkiness when running. A remedy was achieved by coupling the tender closer to the locomotive and thus raising the compression of the buffer springs.
Not until the lines were upgraded in 1910 to take a 17-tonne (16.7-long-ton; 18.7-short-ton) axle load, could the necessary reinforcing measures be taken. The S 6 then became the heaviest 4-4-0 locomotive on continental Europe, even outweighing the subsequently built four-cylinder, saturated steam locomotives of Class S 7.
The driver's cab was initially built with a tapered front and conical smokebox doors in order to reduce wind resistance. An unfortunate side effect of the streamlined driver's cab, however, was that the engine crew were dazzled at night by reflexions from the diagonally oriented front window panes. From 1908/1909 the cab was built with a flat front.
The locomotives were equipped with Prussian Class pr 2’2’ T 21.5 tenders.
Read more about this topic: Prussian S 6
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