SNCF 4-8-4 Locomotives in France

Class 242.A1 (Locobase 1063)

Much of the data from Thierry Stora's French Compounds site ([], accessed 19 August 2007). (Thanks to Alexander Blessing for his 4 March 2022 email containing the phrase "reinforced compound" of which Locobase had not heard. He also noted the valve gear ID, boiler pressure, and the road number as well as commenting on the different tractive effort values he had found.)

One of the largest engines ever to run in Europe, this one-of-a-kind design is considered to be Andre Chapelon's valedictory.

Its foundation was the 241-101 experimental three-cylinder engine that had appeared in 1938, but not particularly impressed. In 1943, Chapelon began converting the 4-8-2 according his own precepts. He adopted many of the innovations from other builders and added several of his own. The firebox had a combustion chamber and two Nicholson thermic syphons. A triple Kylchap exhaust system replaced the more typical blast nozzle.

In addition to the unusual one HP, two LP cylinder layout, the design included two 200 mm x 190 mm (7.87" x 7.48") Trick slide valves for the HP cylinder, one Willoteaux slide valve (380 mm x 150 mm / 15" x 5.9") per LP cylinder.

Stora explains the valve operation in detail, the essence of which is: When the 242 coupled to a heavy train (1,000 tons or more), one started this massive locomotive as a simple-expansion system "...formed by the two L.P. cylinders helped and partially fed by the H.P. cylinder functioning under the difference (fixed by the pressure reducer) of pressure between its steam chest and the one in the intermediate receiver." Pretty neat. This may be the "reinforced compound" setting that Blessing mentions when he assesses John van Riemsdick "Compound Locomotive" report that tractive effort could reach 26 metric tons (57,320 lb). Blessing adds "I have no definitive proof of this, but the locomotive was capable of running as such."

Then, at about 15 mph (25 km/h), the driver closed the LP regulator and opened the HP regulator fully (partial opening led to high losses of efficiency according to Chapelon) and the engine now operated as a full compound. At all other times, the engine started in the compound mode with the regulator fully opened.

In one test, pulling 611 tons of train at 56 mph, this locomotive developed 4,200 hp. Intended to be a class leader, it was orphaned by the French decision to electrify. A 2-10-4 would have been a freight-service companion.