Petite Ceinture 4-6-0 Locomotives in France

Class 51 (Locobase 8913)

Data from Railway Engineer, June 1908, p 185-186, corrected by Institution of Mechanical Engineers (March 1904), p. 363. See also "Four Cylinder Tandem Compound Locomotive, Ceinture Railway of Paris", Locomotive Magazine, Volume 18 (15 October 1912), pp. 209-210, and A Biel, "Nouvelles Locomotives de la Petite Ceinture", La Nature, No 1549 (31 Jannier 1903), p. 129-130.

The inner belt railway around Paris had special requirements, one of which was a need to restrict axle loading to 16.2 tons. La Nature's account spelled out the taxing operational environment by noting the Petite Ceinture's length of 32 km (19.9 miles) was speckled with 28 stations separated by 600 to 1,500 metres (0.38-0.93 miles) of running distance. This meant abrupt and irregular stops and starts.

Although the trailing tonnage totaled about 100 tonnes (110.2 short tons), the sudden demands for power combined with a goal of dropping circuit time (Courcelles-Ceinture to Courcelles-Ceinture) from 80 minutes to 65 minutes. Combine that target with the ever-present desire to reduce coal and water consumption and a four-cylinder compound starting as a simple-expansion engine seemed the best choice to locomotive superintendent Gaston du Bousquet

According to the author of the June 1908 article:"The adoption of the tandem arrangement of the cylinders was decided upon with a view to eliminating- the weight of the two additional sets of valve gears commonly used in France in connection with four cylindered compound engines."

The arrangement consisted of an HP cylinder in front of an LP cylinder on each side of the smokebox. "The exhaust from the h.p. cylinders flows direct to the steam chest of the l.p. through rotating intercepting valves," explained the author, "these latter valves also acting as starting valves, being automatically moved by a small air motor which is set in motion when the regulator is placed in full open position."

Unusually for tandem cylinders, the LP (front) did not abut the HP cylinder (rear). Instead the rods for the piston and valve in each cylinder were joined by couplings between the two cylinders. Apparently, the connections were both rigid and sturdy enough, assisted by extending the piston rod through the cylinder front and very likely the characteristic French railway devotion of crew to the care of their engine, to permit decades of operation.

The boiler featured a Belpaire firebox and outside steam pipes directly down from the dome to the HP cylinders. In the 1930s, only the 52 gained a trailing axle, thus becoming a 4-6-2T. Only six remained in service when the SNCF was formed in 1938.