Midi 4-6-2 Locomotives in France

Class 3 001/231 B (Locobase 20975)

Data from "Fichier:231 3001 01 MM.jpg" on the WikiMidi website at

[], last accessed 9 January 2022.

Sixteen locomotives introduced the Pacific layout in a typically French four-cylinder compound setup, Belapaire trapezoidal firebox, and short cab. They weren't delivered with superheaters and apparently never received them during updates.

In 1925 the Midi began fitting the ACFI feed water heater to 3001, 3005, 3009, and 3015.

Class 3 051/231 C (Locobase 5325)

Data from "231 nñ 3 051 a 3 054 puis 231-051 a 054 du Midi" on the WikiMidi website at [], last accessed 9 January 2022; and table published in Railway Mechanical Engineer (RME) in May 1916. Identification of the actual class from [] (visited 29 May 2004).

Sauvage's table gives exactly the same adhesion weight for the Midi's TenWheeler and for the two Pacifics he provides data for. This arises from the firm 18 tonne axle loading for the lines on which they all worked. This quartet repeated the non-superheated 3.001 design shown in Locobase 20975, but traded small tubes for 24 superheater flues and increased high-pressure cylinder diameters by 30 mm (1.18").

In 1925-1932, 3.054 was fitted with a DM superheater with 24 elements. 3.051's 24-element superheater was replaced by the 28-element superheater fitted in the 3.100 class (Locobase 5326).

Class 3 101/231 E (Locobase 5326)

Data from diagram UG Type 159, Societe Alsacienne de Constructions Mecaniques from locomotive book supplied by Dany Machi up at [] as Diagrammes des machines SACM construites a GRAFENSTADEN (October 2007). See also "2-cylinder locomotive for the Midi Railroad of France", Railway Mechanical Engineer, Volume 97, No 2 (February 1923), p.86; and I N Jevica's [] (visited 29 May 2004). The locomotive mentioned in the RME table must have been a prototype.

This was not a particularly attractive locomotive. The bulk of the boiler and firebox and small cab windows managed to diminish the apparent size of the relatively tall drivers. A very small steam dome sat well forward over the first coupled axle, separated from a short, thin stack by an equally undersized sand dome. A second sand can flanked the dome from the rear. Also less aesthetically pleasing was the rear truck's position at the very rear of the bobtailed cab.

Locobase wonders if the Midi had a pinched loading gauge with especially constricted vertical clearances that, combined with the need for a large boiler diameter, forced the designer to go small along the top.

Yet the design of the locomotive seems to have sought greater efficiency in steam production than the earlier Midi engines shown in Locobase 5325 while reducing maintenance. For example, small-tube counts dropped by in favor of adding four more superheater flues. The result, RME reported, was that "heating surface and grate area remained practically the same, but the volume of gas through the large flues was increased from 40 per cent to 47 percent." Perhaps more important, superheater area increased by about 20%.

Both the cylinder layout and the firebox design changed as well. A typically French four-cylinder compound setup gave way to a two-cylinder simple expansion design because the latter's simplicity reduced maintenance demands at little cost to efficiency. Dropping boiler pressure by about 40 psi (2.75 bar) undoubtedly reduced the strain on the round-topped boiler.

RME reported that the 3100s hauled an average trailing load of 254 tons while consuming 13.5 kg per km (47 lb tons per mile).