The Holcroft-Anderson Recompression Locomotive.

Updated: 1 Apr 2008

New: Engineering reference added

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Above: The Holcroft-Anderson Recompression Locomotive A186 in Eastleigh works, June 1933.

The Holcroft-Anderson Recompression Locomotive had a long and complicated history which I won't explore deeply at present.

In brief, engineers Anderson & McCallum had invented a process for the recompression of exhaust steam to improve efficiency; this was proven to work in a static installation at Surbiton power-station in 1927-29.
Harry Holcroft, Technical Assistant to Maunsell of the Southern Railway, visited the installation in 1927 and was impressed with the concept. A controlled test at Surbiton with Holcroft present showed a 29% fuel saving compared with atmospheric working.

Vapour recompression, as it is called today, is a perfectly sound thermodynamic process. If you need some steam at modest pressure, it is often more economic to compress the exhaust vapour and reuse it rather than generate more steam at high pressure in the boiler. Today this recompression is done either by steam-powered ejectors or electrically driven centrifugal compressors, usually to provide process steam.

A locomotive converted to use the process was delivered to the Southern Railway (UK) in 1930. Details of the steam cycle are somewhat obscure, but included an evaporative cooler and exhaust compressor on each side of the boiler.
Steam was raised in the boiler, passed through the cylinders and then, via grease-separators, to evaporative coolers either side of the engine, part-filled with water from the tender. The steam was only partly condensed; cooled and greatly increased in density, it was recompressed by compressors driven by vertical steam engines each side of the firebox, and re-entered the boiler via clack boxes either side of the steam dome. These engines also drove gear-type boiler feed pumps. A valve allowed conventional working with the cylinder exhaust going through a blast-pipe; this was used for starting.
A steam-driven fan attached to the inside of the smokebox door provided the draught; as originally manufactured this worked backwards, blowing smoke out of the firebox door. A quick redesign of this feature was called for, but the fan draught system still seems to have given a quite excessive amount of trouble.

The loco was put through trials until 1934, suffering various problems, especially with the draught fan, until once again those concerned appear to have lost interest for no obvious reason. The engine was reconverted to standard form in 1935.

Here are some nuggets of hard fact:

Steam conditions
200 psi
Wheel layout
2-6-0
Weight
66tons 4cwt

Details of the design were published in the journal Engineer:

See Holcroft, H. "Condensing by compression a locomotive experiment". Engineer, 1946, 182, 202-3; 227-9; 248-9. With 3 illustrations, 3 diagrams, table.
There was further discussion on this topic by H.H. Carr and Oliver Lyle in Engineer, 1946, 182, 327; 350; 446: 183, 89-91. (See Duffy)

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