2-6-4 Steam Locomotives in Switzerland

Class Ea 3/6 (Locobase 20311)

Data from "Heizdampf-Tenderlokomotiven, Serie Ea 3/6 der Bern-Neuenberg-Bahn", Schweizerische Bauzeitung, Bd LXII [52], Nr 18 (1 November 1918) pp. 250-252, archived at [], last accessed 12 September 2024; "2-6-4 Tank Locomotive, Berne-Neuchatel Railway", Locomotive Magazine, Volume XX [20] (15 June 1914), p. 150; and "BN Ea 3/6" in Wikipedia at [], last accessed 12 September 2024. Works numbers were 2350-2352 in 1913.

The remarkable thing about this pair of locomotives, apart from the four-cylinder layout and the toy-like 850-mm (33.5") diameter trailing bogie wheels, was their owner. At the time of their production in 1914, the B-N was the only large railway in Switzerland not owned by the government. Comprising an impressive list of subsidiary lines like the 43 km (26.7 mile) BN, the Berne-Lotschberg-SImplon amalgamation included the (Thun/ScherzligenvInterlakenvBenigen, Scherzligen-Brigue, Berne-Schwarzenberg, Berne-Thoune (via Belp), Gruben Valley, and Spiez-Zweisimmen.

The fixed wheelbase for the drivers measured 1.70 m (5 ft 7 in) and included two of the three axles.

Wikipedia gives a detailed explanation for the surprisingly steep cylinder angle of 1:8. All four cylinders lay in line abreast under the smokebox and drove on the middle axle. That wasn't uncommon for four-cylinder simple-expansion locomotives. but SLM set up the quartet in unusual ways. Using inside-admission piston valves meant setting the inner cylinder cranks on each side 180 deg from the outer cylinder on that side. Settings from one side to the other were 90 deg. As a result, the valve gear could control both cylinders on the same side.

The outer two connecting rods faced no obstruction, but the inside pair had to clear the leading ashesion axle, hence the steep rake on the cylinders. In many four-cylinder setups, a listener would hear the flutter of eight pants of steam per driver revolution. In the Ea 3/6, only four "beats" would be heard because of the synchronized cycles on each side.

Limited to 90 kph (56 mph) typical maximum speed, the Ea 3/6 hit 105 kph (65 mphj) during trials. One of these powerful engines could pull a typical trailing load of 300 tons up a 1.8% grade at 40 kph (25 mph). But BN found the fuel and water consumption of four simple-expansion cylinders was, according to Google's translation of the Wikipedia account, "anything but economical." Such excess of potential combined with a high axle loading limited its utility on much of the system.

Like many 20th century steam locomotives, the Eas' careers ended prematurely as they were displaced by the BN's electrification in 1928. By 1933, the two were taken out of service and scrapped.