NON-STANDARD BR CLASS 9Fs

Masterclass Looking at railways in detail

The BR Class 9F marked the pinnacle of steam locomotive design in the UK but, as NICK BRODRICK explains, the large fleet featured a couple of non-standard versions.

Robert Riddles’ Standard ‘9Fs’ were highly successful goods locomotives; arguably the best ever built for this country before dieselisation. Certainly, the most modern. It might seem odd therefore that British Railways’ Chief Mechanical Engineer seemed hasty in launching a very un-Standard sub-division of the class, less than 18 months after the first conventional 2-10-0s were outshopped from Crewe.

However, the Attilio Franco-Dr Piero Crosti adaptation had been baked in from the early development of the ‘9F’.

The proposal was seemingly cemented sometime around 1950/1 when E.S. Cox, who sat on BR’s Design Panel, spent part of his family holiday to Italy poking around Venice loco shed while discussing the principles of pre-heating with Dr Crosti himself and travelling on the footplate of his machines.

With his colleague Attilio Franco, the Italian engineers had developed a system for pre-heating water before it was fed into the boiler. Instead of exhaust gases being ejected through the smokebox chimney, they were ‘u-turned’ through a cylindrical preheater slung beneath the boiler (or two either side) and exhausted via a nozzle(s) towards the cab end. This pre-warmed, jacketed water was then injected into the boiler at a temperature not much less than its nominal working temperature.

1950s Britain was facing an acute shortage of coal, with rising costs and quality of supply reducing

With 1950s Britain facing an acute shortage of coal in the post-war austerity age, BR was under pressure from the government to shave half a million tons from its annual usage. At that time that consumption was around 14 million. Costs were rising sharply, and quality of supply reducing.

Italy and West Germany had successfully built (and modified) locomotives with this Franco-Crosti system, which had showed the system capable of up to 20% reductions in coal burning.

Wisely, BR bought the Italian patented design on a sliding scale of performance efficiency payments: £800 if 18% was achieved, down to zilch if it fell below 12%.

The theory was that the costs of tweaking/re-engineering the ‘9Fs’ would be offset by the operational efficiency savings from the ten ‘9Fs’ that were already in production and/or complete by the time work began on No. 90020 at Crewe and what would become its nine ‘Crosti’ sisters, Nos. 92021-92029. Mechanically, they were virtually identical, as well as the BR1B high-sided tender. It was the boiler that required the most drastic alteration.