SNCB 2-8-2 Locomotives in Belgium

Class Type 5 (Locobase 20839)

Data from data card "Type 5 - Belgische Stoomlokomotieven - 2-8-2 Mikado", Fiche #264, demijilpaal, supplied by Jonathan VanAken in a 3 February 2021 email that included several accounts of this quartet. (Many thanks to VanAken for filling a rarely referenced class.)

The various accounts all agree: the Type 5 was at least problematic. They were designed to pull 600 ton loads up a 1/6% grade at 40 km (25 mph) in a combination that outstripped the 2-8-0s in grate and firebox size. In the mid-1920s, Belgian State's design department first examined in 1924 a four-cylinder line-abreast compound layout that would enter service later as the core of the Type 8 (later Type 7) 4-6-0s. Another option considered reproduced the lines and dimensions of the Prussian State Railways' massive type 2-10-2 tank locomotive.

In addition to the increased freight tonnage, the trains would need to reach 100 kph (62 mph) and the Mikado layout of four coupled axles and leading and trailing trucks proved the winning arrangement. Tests using PLM and KPEV P10 (Locobase 1126) 2-8-2s completed in September 1928 confirmed the decision.

Clearly, the design emphasized power at speed as expressed in horsepower. Two big "square" (bore=stroke) simple-expansion cylinders encompassed a volume unmatched anywhere other than in North America. 330 mm (13") piston valves supplied the cylinders with steam generated by a large grate and superheated to a very high degree to drive the third coupled axle. An ACFI feed water heater had a 21,687 litres (5,730 US gallons). (The Belge superheater was designed by Flamme; it seems to have been a four-loop system similar to the Type E superheater used by many modern North American locomotives.)

Soon after the class's introduction, the design showed poorly designed internal steam passages, high coal consumption, too much cylinder volume. Power generated by the big cylinders stressed the rails, as did the locomotive's high weight and axle loading.

501 tested smaller cylinders (680 mm/26 3/4") in March 1934, but results showed continued high coal consumption and sooty deposits on the superheater elements. Three months later, tests of a new setup saw a 25% drop in coal consumption.

1935 saw the installation of 4.5 sq m (49.5 sq ft) of water tubes in the brick arch. Even so, the boiler simply didn't produce enough steam, in part because the brick arch reduced the grate area, and superheater temperatures failed to impress.

Such lemons needed drastic remediation and two solutions were considered, said Vapeur en Belgique, Volume 2. One was to modify the valves by drawing on recent design work on the Type 1 (Locobase 2601). In addtion, the shops would replace the Belge superheater with a two-loop system produced by the Superheater Company (US owner of the Schmidt patents). Much simpler than overhauling the valve train was the option to enlarge the piston valve diameter to 345 mm (13.59") and making the other changes. This is the path they chose.

Apparently these modification worked well enough. The four Mikes served the Belgian railways throughout World War II, their railways' maximum speeds reduced from 120 kph to 90 kph and on into the early 1950s.

NB: The data fiche's tube heating surface calculaton reflected the interior diameters of the tubes and flues. Together with the firebox area, the result came to 286.05 sq m (3,079 sq ft). Calculating the tube heating surface from the outside diameters given in the data fiche yields the figure shown above.