OKl2

OKl2-6, loco depot in Jaworzyna Śląska, August 4, 2004…

…another view of the same machine, photo taken on October 11, 2000…

…and yet another picture, taken on the same occasion.

Things are improving: OKl2-6 is no longer posing like she did before, but its condition has greatly improved. Photo taken on October 28, 2005

Side drawing of the DR class 64 by K.-E. Hertam (TB vol.2)

Ex-DB 64 305, owned by Nene Valley Railway and awaiting overhaul. Wansford, UK, July 23, 2005.

Two photos from my collection, albeit of rather poor quality: 64 035 (Krupp 964/1928)…

…and 64 109 (Jung 4064/1928). Details are lacking, but both look like factory photos.

After WWI, German railways (DR) faced the difficult problem of rolling stock unification. The Locomotive Commission, formed in 1921, was entrusted the complex task of replacing diverse mixture of types inherited from individual lands’ railways with new family of modern machines, to serve throughout the entire state.

Among other classes, it was soon decided that a light tank locomotive for local traffic, with axle load about 15 tons, was necessary. The 1-3-1 axle arrangement was chosen, although this layout had been almost unknown in Germany, apart from a handful of very unsuccessful Prussian T6s. First preliminary drawings were submitted in 1922 and, after some dispute concerning basic features (including the very layout – some argued that 1-3-2 would be more suitable), Henschel company was asked in September 1924 to prepare the detailed design. This was accomplished in 1925 and after some further modifications the machine was accepted as class 64. It should be noted that the intention of normalization was realized to a considerable degree: over 79% parts were interchangeable with other classes.

First eight machines were built by Henschel in 1927 and production continued until the end of 1940 to reach 520 examples. By German standards this was not a particularly great number; it is thus somehow surprising that these locomotives were built by as many as fifteen factories. This was intended to keep the German locomotive industry busy, but in the end did not prevent many of these companies from going bankrupt, especially between 1929 and 1931. Thus, class 64 was built by AEG (6), Borsig (13), Esslingen (45), Hagans (14), Hanomag (21), Henschel (31), Humboldt (21), Jung (99), Krauss-Maffei (66), Krupp (65), Linke-Hoffmann (13), Orenstein & Koppel (51), Union-Giesserei (40), Schichau (12) and Vulcan (23). Orders for further forty machines from Jung and fifty from Orenstein & Koppel were cancelled. There were minor differences, depending on the manufacturer, some new design features were also tried. Ten machines had Krauss-Helmholtz trucks instead of Bissel idle axes; twenty-seven had their piston feedwater heater pumps replaced by Friedmann-type injectors; and one was fitted with Lentz-type valve gear (which, despite better economy, proved unreliable, so its development was not proceeded with).

Class 64 proved very successful and found widespread use. It was suitable not only for local traffic, but also for light trains on main lines. After WWII most of them remained in Germany (280 with DB and 115 with DR). They were also used in Austria (only one), Czechoslovakia (about 65, as class 365.4) and Soviet Union (7, as class TY).

After WWII Poland took over thirty-seven examples, plus one handed over by Soviets. They were designated OKl2 and all were given PKP serial numbers. Some sources claim, however, that one of these machines (namely OKl2-1) was in fact a Hungarian class 342 – at least this is what has been deduced from boiler serial number! This question still remains to be solved. Just like in pre-war Germany, they turned out to be quite versatile, serving mainly with suburban and local passenger trains. Five machines were written off until 1956, but rapid withdrawal of this type began in mid-60s. Two remained in the PKP inventory until 1973. The OKl2-6 (Union 2820/1928, ex-DRG 64 061) was written off in Nysa on November 3 and preserved in the former locomotive depot in Jaworzyna Śląska (now Industry and Railway Museum). The last one – OKl2-20 – survived in service only few days longer: after being written off on November 20 in Malbork, it was kept there for further four years and, unfortunately, finally scrapped. As many as fifteen machines of this popular class have been preserved in Germany, many of them in working order. Single examples were sold to Great Britain (Krupp 1308/1934, former DB 64 305, purchased in 1973 by Severn Valley Railway, in 1985 sold to Nene Valley Railway, now awaiting overhaul), the Netherlands (Jung 7006/1937, former DB 64 415, now operational with Veluwsche Stoomtrein Maatschappij of Beekbergen) and Belgium.

Main technical data

No.	Parameter	Unit	Value
1.	Years of manufacture	-	1927 – 1940
2.	Total built / used in Poland	-	520 / 38^3)
3.	Tender class	-	-
4.	Axle arrangement	-	1-3-1
5.	Design maximum speed	km/h	90
6.	Cylinder bore	mm	2 X 500
7.	Piston stroke	mm	660
8.	Engine rating	kW/hp	580 / 790^1)
9.	Tractive effort	kG	9 700
10.	Boiler pressure	MPa	1.43
11.	Grate dimensions	m X m	1.9 X 1.07
12.	Firebox heating surface	m^2	8.7
13.	Distance between tube plates	mm	3800
14.	Number of flue tubes	-	114
15.	Heating surface of flue tubes	m^2	53.7
16.	Number of smoke tubes	-	32
17.	Heating surface of smoke tubes	m^2	43.0
18.	Evaporating surface, total	m^2	105.4
19.	Superheater heating surface	m^2	37.4
20.	Diameter of drivers	mm	1500
21.	Diameter of idlers front/rear	mm	850 / 850
22.	Total weight, empty	kg	57 900
23.	Total weight, working order	kg	74 700
24.	Weight on drivers, working order	kg	45 500
25.	Weight with tender, empty	kg	-
26.	Weight with tender, working order	kg	-
27.	Maximum axle load	T	15.3
28.	Axle base (with tender)	mm	9 000
29.	Overall length (with tender)	mm	12 400^2)
30.	Brake type	-	Knorr

1) From 1928 tests

2) 12 400 to 12 500 mm depending on manufacturer and example

3) Possibly OKl2-1 was in fact MÁV class 342

References and acknowledgments

Comprehensive account of this class history and design can be found in the monographic article by Roman Witkowski in SK vol.6/2000. Information on individual examples has been taken mainly from the impressive Ingo Hütter’s locomotive database (available at www.lokomotive.de).