SAR Class 25 Condensor locomotive

[TramFan]

Finaly finished, my scratch built SAR Class 25 locomotive to a scale of 1:55
These locomotives were designed and built in the early 1950's for use in the semi desert arid Karoo region of South Africa. There were 90 in the class the order being split between NBL in Glasgow and Henschell in Germany. It is reported that the loco's could run for up to 400 miles without taking on water. The exhaust steam was piped to the huge condensing tender and condensed back into water and reused in the boiler. In the early 1970's all but 2 were rebuilt as conventional loco's and all but the 2 that were kept were scrapped in 1991.

[ReynoldsSlumber]

Always wondered why no one tried to recapture the steam from steam locomotives, cool to find out that someone did. Fun scratchbuilt model!

[michik]

Originally Posted by ReynoldsSlumber

Always wondered why no one tried to recapture the steam from steam locomotives[...]

Two main reasons:
- Unlike steam ships, steam engines have no handy access to cooling water. I.e., you need big radiators and ventilators to cool down the exhaust steam sufficiently. This means extra machinery, extra weight and also extra train length.
- In 'conventional' steam engines the exhaust steam is used to create the neccessary draught to fire the boiler (it's blown through the stack, which forms a venturi nozzle, thus creating an underpressure in the smoke chamber). In condensor engines you have to provide the draught by other means, typically a turbo fan, which, in turn, is again extra weight and extra complexity.

Long story short:
Condensing the exhaust steam means substantial extra efforts that you want to avoid as long as you can guarantee a sufficient water supply!

[Viator]

As Michik stated, the condensor locos were more complicated than the standard steam locos, so they were more expensive and more failure-prone. Morover, all steam locomotives had relatively low efficiency and therefore burned a huge amount of fuel, but condensing steam engines consumed even more of it, so their efficiency was much worse and operation was more expensive. The economic factor decided that condensing locomotives were used only on routes where water supply would be terribly expensive or impossible, and all because taking a supply of fuel with you was easier than taking a supply of water - for every unit of coal burned, a steam locomotive used more than two units of water. Therefore, for a journey through the desert, a steam locomotive would have to take with it, in addition to a full tender of coal, two and a half similar wagons of water, which of course would reduce the train's useful load by the same amount and would be even more unprofitable.

[Siwi]

The Metropolitan Railway used condensor systems with some success after early failures, as an attempt to keep steam and smoke to a minimum in tunnels. It would be vented at openings in the shallow cut-and-cover tunnels.

Do you have any more pictures of this model and the construction? What is the reason for the choice of 1:55 scale - is this to use HO scale track for narrow gauge?

[michik]

Now that you mentioned it:
A niche where condensor engines were relatively popular were steam tramways.
There too, the intention was to avoid the exhaust steam when trversing densly populated areas. The condensors typically where simple packs of pipes, which had no other ventilation than the air stream that was provided by the train's movement.

Exhibit A
Exhibit B

Naturally, those condensors worked only for the most modest engines, and they became pretty obsolete with the introduction of electric tram cars, anyway.

[TramFan]

Thank you all for the comments, I do have a few pics of construction will have to upload them. Scale 1:55, it was the size of the basic drawing I used and did not feel the need to enlarge or decrease size,