OKl27

OKl27-41 (HCP 270/1932), preserved at Chabowka loco heritage park, photographed in June 2001.

OKl27-26 (HCP 223/1931), displayed at the Railway Museum in Warsaw; photograph taken on May 25, 2005.

This OKl27-10 (HCP 172/1930), owned by PSMK (railway fans society), is plinthed at the Skierniewice loco depot; photo taken on August 6, 2005.

Another photo of the OKl27-10, taken on the same occasion; shorter right water box can be easily seen.

OKl27 side drawing from PNP.

This OKl27-27 (HCP 227/1931) is plinthed at the Gdynia Grabówek loco depot; photo taken on May 31, 2005.

Another picture of the OKl27-27, taken on August 23, 2007.

OKl27-31, photographed somewhere in Poland in August 1959. Photo from my collection.

Very few locomotives acquired by PKP after WWI could be used on suburban lines; this service demanded fast startups and frequent stops, as well as possibility to run at full speed in both directions. Passenger tank locomotives, most suitable for such duties, were few: most of them were Prussian classes T11 and T12 (in PKP service OKi1 and OKi2, respectively) plus several Austro-Hungarian engines, but their combined number was only about 150 and many of them were obsolete. Due to lack of suitable engines, it was a typical practice to use heavier passenger or even freight machines instead, but this was certainly an interim measure. There was thus a need for a light, fast passenger tank locomotive that could also be used with local trains. Initially it was intended to build an improved version of successful Saxon class XIV HT, which was designed specifically for suburban traffic (eleven served with PKP as class OKl101). Soon, however, a decision was taken to design an entirely new and modern machine, retaining only the axle arrangement of the Saxon engine. The task was entrusted to the Cegielski factory of Poznań (HCP); their design was approved by PKP in 1927 and accepted as class OKl27. First four examples were supplied during the next year and production lasted until 1933, when 122 machines had been built, all by HCP. Despite moderate output (from 16 in 1929 to 30 in 1930 and 1932), the order for OKl27s helped to keep the factory busy during the Great Crisis.

Several modifications were progressively introduced, as new engine was initially not entirely satisfactory. After initial experience with Tr21 and Ty23, which were prone to derailing, small idlers – only 860 mm in diameter – were used, but no substantial improvement resulted and the problem was finally solved by replacing in 1930 Adams idle axle with the Krauss-Helmholtz truck. Running, however, remained somehow uneasy above 50 km/h, but this was not a particular shortcoming, as the machine was not intended for high speeds. Another interesting feature was the introduction of variable-length suspension levers which facilitated easy adjustment of maximum axle load from 16 to 17.5 tonnes. In examples from OKl27-21 onwards, due to fractures of side sills, frame was redesigned and strengthened, which resulted in slight increase of overall length and weight. First machines (up to OKl27-70 inclusive) had water boxes of unequal lengths: the right one was slightly shorter, to provide space for the compressor. This was later eliminated, in order to balance mass distribution. Boiler accessories were also progressively modified and electric lighting supplanted petroleum headlights in 1930. As in some other pre-war Polish locomotives, some new design features were also tested, but not all of them eventually found widespread use. OKl27-112 (HCP 291/1933) was fitted with the Wysłouch-type valve gear, which proved in general successful, but somewhat complex (like similar Lentz valve gear in Germany, it was not widely adopted and further development was abandoned). Several examples were fitted with makeshift smoke lifters.

First machines entered service in 1929 in Upper Silesia. Most were, however, directed to the Warsaw railway hub, with heavy suburban traffic. Eight examples were used by the French-Polish Railway Society for passenger traffic on the ‘Coal Trunk Line’. They soon earned a reputation of good, reliable locomotives, well suited to fulfill demands they had been designed for. Suburban traffic remained their prime domain for a long time.

In 1939, most OKl27s were taken over by the Germans. 107 of them were impressed into DRG service as class 75^12-13 (service numbers 75 1201 through 1307). Fifteen were captured by the Soviets, but probably only two (OKl27-55 and OKl27-90) were converted to the 1524 mm track. They retained their original designation (written in Russian script as OKЛ27) and service numbers. The remaining thirteen fell after Fall Barbarossa into German hands and became 75 1308 through 1320. During 1944 and 1945, Soviet forces captured eleven OKl27s, which were later impressed into the NKPS service and never returned. They probably retained their DRG designations. In 1945, four OKl27s were found in Hradec Králové in Czechoslovakia. Three of them (OKl27-117, then DRG 75 1302, OKl27-32, then DRG 75 1228 and OKl27-53, then DRG 75 1249) were impressed into ČSD service as class 358.0 and designated 358.0500, 358.0501 and 358.0502, respectively; the fourth (OKl27-4, then DRG 75 1204) was not re-designated. Their service with ČSD was brief and in 1947 all were returned to Poland. Seven OKl27s were found in Austria; all were returned in 1947. A number of engines (fourteen?), taken over by DB, saw little service, if any, and were written off in 1952. In all, after the war, 95 OKl27s were given new PKP service numbers. Of these, OKl27-20 was badly damaged and was scrapped in late 40s. At first, these comparatively new, modern and valuable locomotives served mainly near Warsaw and in the Upper Silesia. Later, with mounting supplies of TKt48s (despite designation, they were designed for the same role!) and electrification, which progressed rapidly in suburban areas, they were scattered throughout the country.

Rapid withdrawal of this class began in early 70s. In 1972 PKP had ninety OKl27s, but until 1975 their number fell to 74 and in 1979 there was only one (plus three more used by the railway stock repair works in Łapy until 1985). The last machine in the PKP inventory, OKl27-10 (pre-war OKl27-25, DRG 75 1225, s/n 172/1930) was used for switching in Skierniewice locomotive depot until December 1979 and is now plinthed there. Three more locomotives of this class have survived, namely:

- OKl27-27 (pre-war OKl27-65, DRG 75 1254, s/n 227/1931) at Gdynia Grabówek loco depot,

- OKl27-41 (pre-war OKl27-91, DRG 75 1278, s/n 270/1932) at Chabówka rolling stock heritage park,

- OKl27-26 (pre-war OKl27-61, DRG 75 1253, s/n 223/1931), initially preserved at the Praga locomotive depot in Warsaw, finally found its way to the Railway Museum.

All of them are in good condition, but none is operational. Unfortunately, at least three withdrawn OKl27s were scrapped in the 1990s.

It should be noted that OKl27 was in fact the very first machine of entirely Polish origin; all earlier classes built in Poland had either German (Ok22, Ty23) or Austrian (Tr21, Os24) background. This certainly gives it a place in history.

Main technical data

No.	Parameter	Unit	Value
1.	Years of manufacture	-	1928 – 1933
2.	Total built / used in Poland	-	122 / 122
3.	Tender class	-	-
4.	Axle arrangement	-	1-3-1
5.	Design maximum speed	km/h	80
6.	Cylinder bore	mm	2 X 540
7.	Piston stroke	mm	630
8.	Engine rating	kW/hp	685 / 930
9.	Tractive effort	kG	10 300
10.	Boiler pressure	MPa	1.22
11.	Grate dimensions	m X m	2.42 X 1.01
12.	Firebox heating surface	m^2	11.44
13.	Distance between tube plates	mm	4150
14.	Number of flue tubes	-	123
15.	Heating surface of flue tubes	m^2	73.6
16.	Number of smoke tubes	-	24
17.	Heating surface of smoke tubes	m^2	39.11
18.	Evaporating surface, total	m^2	124.15
19.	Superheater heating surface	m^2	42.2
20.	Diameter of drivers	mm	1500
21.	Diameter of idlers front/rear	mm	860 / 860
22.	Total weight, empty	kg	67 680^2)
23.	Total weight, working order	kg	85 100^2)
24.	Adhesive weight, working order	kg	54 200^2)
25.	Weight with tender, empty	kg	-
26.	Weight with tender, working order	kg	-
27.	Maximum axle load	T	16.8^1)
28.	Axle base (with tender)	mm	9 000
29.	Overall length (with tender)	mm	12 863^2)
30.	Brake type	-	Westinghouse

1) Adjusted from 16.0 to 17.5 tonnes (from OKl27-21 onwards, 18.2 tonnes) by changing suspension levers mounting.

2) Up to OKl27-20 inclusive: overall length 12 613 mm, weight empty 61 500 kg, in working order 80 800 kg, weight on drivers 51 800 kg.

References and acknowledgments

Monographic article by Paweł Terczyński can be found in SK 1/1998. Comprehensive account of this class history and design by Michał ‘Doctor’ Pawełczyk can be found at www.parowozy.best.net. For concise descriptons, see AP and PPN. Many interesting details were taken from (or confirmed by) the entry on OKl27 by Tomisław Czarnecki at the PSMK website www.psmk.org.pl.