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The New Zealand Railways Magazine, Volume 3, Issue 7 (November 1, 1928)

Higher Steam Pressure—850 lbs

Higher Steam Pressure—850 lbs.

In the early days of the steam locomotive, steam pressures of something like 50lb. per sq. in were favoured. By degrees this boiler pressure has been advanced to an average level of from 180 to 220lb. per sq. in., and recently there have been many interesting experiments in the utilisation of exceptionally high pressures in the search for heightened power. The American locomotives “Horatio Allen” and “John J. Jervis” are noteworthy contributions in this field, and in Europe a great deal of experimental work has been performed—especially in Germany. Now Switzerland comes into the limelight, giving us a new type of high-pressure steam locomotive which promises to help materially in the search for a more powerful haulage unit.

The new locomotive has been constructed by the Swiss Locomotive and Machine Works, of Wintherur, and is of the 2-6-2 wheel arrangement, with a boiler pressure of 850lb. It is a tank engine intended for passenger service. The water-tube boiler with smoke box, chimney and blast-pipe, is situated above the six-coupled driving wheels. Placed within a cover in front of the boiler is a three-cylinder, high-speed engine, with torque transmitted by gearing to a jack-shaft and connecting rods. The steam engine is designed for singlestage uniflow expansion in three equal cylinders working in parallel. Supported in four bearings, the crank-shaft is fitted with flexible pinions at either end which mesh with gears keyed to the jack-shaft. Single-seat valves control steam admission, and exhaust is controlled by the pistons themselves, these moving on exhaust ports arranged in the central part of the cylinder liner. Cams, arranged on a shaft with lateral displacement, control cut-off. The driving mechanism is arranged in conventional fashion, with the single exception that the connecting rods are linked to the central page 20 portion of the front coupling rods, thereby reducing the adverse influence of spring motion. The principal dimensions of the locomotive are as follows;-Boiler pressure 850lb., grate area 14.4 sq. ft., heating surface 1,940 sq. ft., water capacity of boiler 594 gallons, diameter of cylinders 8 ½ in., piston stroke 13 3/4 in., diameter of driving wheels 60in., weight in working order 75 tons. In recent trials on the Swiss railways the Wintherur locomotive has shown marked economies in coal and water consumption, and it has proved capable of attaining high speeds with heavy trains on stiff gradients.