The Zoelly Swiss Turbine Locomotive.
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
Left: The 3/5 Swiss turbine locomotive in steam.
Left: The locomotive seen from the other side.
Left: Side elevation of the Swiss turbine 3/5.
Left: The Swiss turbine loco under construction.
Left: The early version?
Left: The original 2-6-0 locomotive looked like this.