Updated: 5 June 2007

This locomotive was drawn to my attention by Alex Stirrat, who also provided the pictures and much of the information.

This little-known Swiss locomotive was the first serious turbine design to be built, by SLM/Escher-Wyss/Zoelly in 1919. For some reason it fails to appear in most locomotive books.

It was a conversion of an elderly 3/4 locomotive of the Federal railways. (see bottom of page for a picture of the original type) The "3/4" is the old German/Swiss axle classification system, indicating 3 driven axles from a total of 4. Thus a 4-6-0 and a 2-6-2 are both 3/5, which is not too helpful.

The new locomotive had a 6-stage Swiss Zoelly impulse turbine located transversely in front of the smoke box, a separate 2-stage Curtis turbine being used for reverse. Steam supply was controlled by two sets of valves. The main turbine developed 1200 HP and drove the coupled wheels through two stage reduction gearing with a ratio of 1:28, a jackshaft and coupling rods. Turbine speed was 7500rpm at the planned maximum speed of 75 km/h.
Two surface condensers were placed on either side of the boiler, using cooling water from the tender. This water was returned to the tender by turbo-pumps. The boiler, of the usual locomotive firetube type, had a working pressure of 170 psi.

A condensing system naturally prevents the use of a conventional blast-pipe for boiler draught, and this was supplied by means of a cold-air blower beneath the grate. This very unusual arrangement avoided having a suction fan working in exhaust gases at 300 degC, an approach which gave trouble in many subsequent condensing locomotives, but meant that the firebox was at positive pressure and the blower had to be stopped every time the fire needed feeding.
This highly dangerous system (one hopes the blower and fire-door were interlocked, but history is silent on this point) was soon replaced by a draught fan mounted on the smokebox door.

The German Krupp-Zoelly Turbine Loco of 1922 was a development of this locomotive, a significant difference being a larger condenser housed in the tender.

Left: The Swiss 3/5 turbine locomotive The weight was 115 tons and the planned speed 75 km/h.

Left: The 3/5 Swiss turbine locomotive in steam. Note surface condensers each side of the boiler. These were cooled by water from the tender; this water was itself cooled by intimate contact with the air as it was sprayed from a series of pipes in the tender. The overall water consumption was about half that of a conventional locomotive. The perforated streamline nose held a turbine-driven draught fan; the suggestive pipe visible running into this casing may have been the fan steam supply, but this is speculation.

Left: The locomotive seen from the other side. This is probably one of the official photographs, and gives a good view of the jackshaft drive. Note that this cutting-edge locomotive still has an oil lamp on the front.

Left: Side elevation of the Swiss turbine 3/5. This gives a better view of the cooling tender.

Left: The Swiss turbine loco under construction. The turbine shaft can be seen just in front of the smokebox. Bibliography: Un.

Left: The early version? This rather enigmatic picture appears to show the locomotive just after its completion. However, there is no sign of the condensers. The smokebox looks normal, so the extraction fan is not installed. There are three intriguing pipes leading from the side of the boiler down to the turbine, which probably feed the turbine nozzles. From Modern Power Engineering, by A Regnauld, pub Caxton 1924. Vol 1, p15.

Left: The original 2-6-0 locomotive looked like this. It was clearly a radical conversion; very little appears to have been unchanged.

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