The reference for locomotives and railcars


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Prussian T 6
Polish State Railways OKl1
Germany | 1902 | 12 produced
Die Lokomotive, June 1904

At the beginning of the century the Berlin city, ring and suburban railways had a need to replace the four-coupled locomotives with more powerful ones. The requirements here included to accelerate a 240-ton passenger train consisting of 14 cars between the stations to a basic speed of 60 km/h. At that time, those responsible still saw difficulties in meeting these requirements with electric traction. Thus, Wittfeld ordered powerful six-coupled tank locomotives. Since the axle load permitted 17 tonnes instead of the 14 tonnes of the Vienna city railway, this was favorable to achieve the required performance.

In addition to the conventional superheated two-cylinder T 11 and T 12 engines, the T 6 was also developed, which operated with saturated steam but had three generously dimensioned cylinders. While the outer cylinders were installed between the leading axle and the first driving axle as usual and acted on the second driving axle, the inner cylinder was located horizontally in front of the leading axle and acted on the first driving axle. The leading axle was designed as an Adams axle, while the trailing axle, together with the third driving axle, formed a Krauss-Helmholtz bogie. A Langer-Marcotty design smoke-consuming device was used in the boiler, which burned the soot in the firebox by supplying air from the top.

The tests had shown that the cylinders were oversized compared to the boiler and led to a high coal consumption. They were also too large compared to the adhesive weight, resulting in an adhesion coefficient of less than three and meaning that the locos often slipped when starting. Furthermore, the required acceleration performance could not be achieved, while the more economical T 11 and T 12 achieved it. So the twelve pre-series engines of the T 6 remained.

Two of the twelve engines went to the Altona division. The middle cylinder was removed from the Berlin engines by 1908. They were mainly used for express freight trains and as temporary help at times of heavy traffic, while their sisters, which were clearly outnumbered, pulled the suburban trains. In 1913 they were relocated to other divisions, so that after the First World War five examples served as OKl1 with the PKP. The locomotives remaining in Germany were retired shortly after the end of the war, so that they did not receive Reichsbahn numbers.

Axle config2-6-2T (Prairie) 
Gauge4 ft 8 1/2 in (Standard gauge)
Dimensions and Weights
Length43 ft 11 9/16 in
Wheelbase29 ft 6 5/16 in
Fixed wheelbase12 ft 5 5/8 in
Empty weight136,686 lbs
Service weight172,225 lbs
Adhesive weight111,267 lbs
Axle load37,479 lbs
Water capacity1,770 us gal
Fuel capacity5,512 lbs (coal)
Power sourcesteam
Estimated power738 hp (550 kW)
Optimal speed11 mph
Top speed47 mph
Starting effort42,144 lbf
Power Plant
Driver diameter59.1 in
Boiler pressure203 psi
Expansion typesimple
Cylindersthree, 19 11/16 x 24 13/16 in
Grate area24.8 sq ft
Firebox area128 sq ft
Tube heating area1,533.9 sq ft
Evaporative heating area1,661.9 sq ft
Total heating area1,661.9 sq ft
Calculated Values
steam locomotive
tank locomotive
last changed: 09/2022

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