BR Standard Class 9F 92020-9

British Railways Standard Class 9F steam locomotives Nos 92020-9 were experimentally built with Franco-Crosti boilers, thus forming a subclass.

Limitations of the British loading gauge meant that the original BR9 boiler had to be reduced in diameter to allow for the preheater drum below it.

[1] In the event, the experiment did not deliver the hoped-for benefits, and efficiency was not increased sufficiently to justify the cost and complexity.

The Crosti preheaters also proved to be a problem for maintenance, owing to acidic fluegases condensing in the feedwater heater and causing corrosion.

[2] All were fitted with the British Railways standard BR1B-type tenders which had a water capacity of 4,275 imperial gallons (19,430 L) and carried 7 long tons (7.1 t) of coal.

Crosti 9F 92021 at Wellingborough shed in 1959, showing the unique layout on the right hand side of the loco
9F 92022 in 1964; the preheater drum had been sealed off in June 1962
9F 92029 in 1964