The Holcroft-Anderson Steam-Recompression Locomotive (A186) was a locomotive well before its time.
In 1927, Harry Anderson and John McCallum had invented a process for the recompression of exhaust steam, which could then be reused - to prove this concept worked, they built an exhibit of their work at the privately owned Surbiton Power Station.
It wasn’t long before Harry Holcroft, the the Technical Assistant to Richard Maunsell (Then chief engineer of the Southern Railway) was investigating the process - visiting the so called ‘Steam Heat Conservation Co.’s exhibit. He was impressed, a 29% fuel saving being recorded, and reported back to Maunsell with flying colours.
In 1930, a locomotive converted to the use the system was delivered to the Southern Railway.
The locomotive was sound in principle. Steam was raised and used in the usual way, and then, via grease-separators, to coolers either side of the engine, part-filled with water from the tender; the steam from this was piped to the funnel. The steam in the cooler pipes was partly condensed, very high in density. It was recompressed by compressors driven by vertical steam engines each side of the firebox - and from there, back into the boiler for further use.
The bizarre contraption on the front of the smokebox was a steam driven fan, which was used to provide draught. It was manufactured in such a way it ran backwards, blowing out smoke and dust. It was redesigned accordingly.
It was the aforementioned fan that prevented the locomotive from going further - it was a horrifically inefficient, tending to break down more than the condensing system, that in contrast worked well.
The engine was trialled repeatedly until 1934, when those behind the idea simply abandoned the concept - by 1935 the engine was converted back to a standard engine, and modernisation of steam locomotives, just as it seemed likely, stalled once again.