TKr55

 

 

The sole TKr55-1, photographed at an unknown location in April 1959. Photo from my collection.

 

 

TKr55 side drawing from PPN.

 

 

 

After WWII Polish state railways PKP obtained 575 American freight engines of the S-160 Consolidation type, classed Tr201 (supplied by UNRRA – 75 examples) and Tr203 (purchased from USATC stocks – 500 examples). They were among the most important PKP locomotives during the first post-war years and often ran with passenger trains. Their running qualities, however, left something to be desired; they also had several minor shortcomings, resulting mainly from simplified design. In early 1950s these locomotives were shifted to switching or withdrawn and kept in reserve.

Due to modern boiler design and comparatively high efficiency, in 1952 it was decided to marry their boilers with the undercarriages taken from Ok22 passenger engines. This hybrid was classed Ok203 (later Ok55) and two examples were converted between 1952 and 1953. As results were considered satisfactory, plans were eventually drawn to utilize all available Tr201s and Tr203s in such manner. As a ‘by-product’, it was decided to use the S-160 frame and wheelsets to build a tank engine, fitted with a new boiler. Such locomotive would be suitable for local traffic, both freight and passenger, as well as capable to supplant a motley collection of obsolete and inefficient switchers then in use with PKP and industrial operators.

Detailed design was completed in 1955. The prototype was built by ZNTK (Railway Stock Repair Works) of Wrocław in 1957 and designated TKr55-1. Original frame, wheelsets and steam engine were almost unchanged, apart from local frame strengthening; rear coupled axle was given side-play of ±20 mm, in order to allow negotiating curves 120 m in radius. New boiler, of welded construction, was based on that of the TKt48 tank locomotive then in production, but shortened by almost 900 mm, married with the Tr203 superheater and fitted with the rocking grate. Water and coal boxes, as well as the driver’s cab, were also patterned on that of the TKt48. TKr55 turned out as a successful engine, with low fuel consumption and ability to burn low-grade coals. It, however, appeared too late. In 1957 it was decided to terminate the development of steam locomotives in Poland and concentrate on rapid electrification and diesel power. No more TKr55s were thus built. The prototype was used for switching in Kutno until 1972; unfortunately, it has not been preserved.

It may be argued that termination of steam traction development in Poland was premature. Forecasts of electrification progress proved over-optimistic and introduction of diesel power progressed nothing but smoothly. In effects, obsolete and uneconomical steam switchers remained in use well into the 1980s.

 

 


Main technical data

 

No.

Parameter

Unit

Value

1.

Years of manufacture

-

19571)

2.

Total built / used in Poland

-

1 / 1

3.

Tender class

-

-

4.

Axle arrangement

-

1-4-0

5.

Design maximum speed

km/h

70

6.

Cylinder bore

mm

2 X 483

7.

Piston stroke

mm

660

8.

Engine rating

kW/hp

 440 / 600

9.

Tractive effort

kG

 12 000

10.

Boiler pressure

MPa

1.63

11.

Grate dimensions

m X m

1.7 ´ 1.188

12.

Firebox heating surface

m2

12.0

13.

Distance between tube plates

mm

3 300

14.

Number of flue tubes

-

97

15.

Heating surface of flue tubes

m2

46.3

16.

Number of smoke tubes

-

30

17.

Heating surface of smoke tubes

m2

38.8

18.

Evaporating surface, total

m2

97.1

19.

Superheater heating surface

m2

42.0

20.

Diameter of drivers

mm

1450

21.

Diameter of idlers front/rear

mm

838 / -

22.

Total weight, empty

kg

69 000

23.

Total weight, working order

kg

85 000

24.

Weight on drivers, working order

kg

63 000

25.

Weight with tender, empty

kg

-

26.

Weight with tender, working order

kg

-

27.

Maximum axle load

T

18.5

28.

Axle base (with tender)

mm

7 087

29.

Overall length (with tender)

mm

11 547

30.

Brake type

-

Westinghouse

 

1)      Reconstruction. 

 

References and acknowledgments

 

-        PNPP, PPN.