Duplex Locomotive - A Successful French Duplex

A Successful French Duplex

In France, the duplex type was made famous by the ten 2-4-6-2 (151A) compound locomotives built in 1932 for the Paris-Lyons-Marseilles company (P.L.M.) to haul heavy freight trains on the 0.8% grade between Les Laumes and Dijon. The performance was so good, the company wanted to order more engines, but the nationalization of the railways in 1938 stopped all projects. These duplex engines were fitted with Lenz-Dabeg rotary cam valve motion and soon thereafter with double exhaust. The low-pressure cylinders drove the first coupled axle, and the high pressure cylinders the second set of axles. Both groups of drivers where linked with inside connecting rods through inside cranks on the 2nd and 3rd drivers, making this locomotive a true 2-10-2, The driving wheels had a diameter of 1.50m (4'11"). The highest permissible speed was 53 mph. In a test on December 19, 1933, the engine developed slightly more than 3000 hp at the drawbar over a distance of 37 miles and a speed of at least 46 mph, without being overworked. In ordinary service these engines could haul 1375 U.S. tons, sustaining 31 mph at the summit of the 0.8% Blaisy grade. After electrification of the line, the 151A were sent for service in northeastern France. They were withdrawn from service in 1956 and scrapped.