page_title: Condensing steam locomotive
section_title: Underground railways
hierarchical_section_title: Condensing steam locomotive / Purpose / Reduced exhaust emissions / Underground railways
caption_attribution_description: Metropolitan Railway A Class locomotive #23, London Transport Museum
context_page_description: A condensing steam locomotive is a type of locomotive designed to recover exhaust steam, either in order to improve range between taking on boiler water, or to reduce emission of steam inside enclosed spaces. The apparatus takes the exhaust steam that would normally be used to produce a draft for the firebox, and routes it through a heat exchanger, into the boiler water tanks. Installations vary depending on the purpose, design and the type of locomotive to which it is fitted. It differs from the usual closed cycle condensing steam engine, in that the function of the condenser is primarily either to recover water, or to avoid excessive emissions to the atmosphere, rather than maintaining a vacuum to improve both efficiency and power.
context_section_description: Originally developed for the Metropolitan Railway to allow their locomotives to work the tunnels of the London Underground. This system was devised by Daniel Gooch and developed by Beyer Peacock. Steam is diverted from the exhaust steam pipes into the water tanks via condensing pipes within the same tanks. The water in the tanks could quickly heat up near boiling point, reducing the condensing effect on the exhaust steam. It was not unknown for the tanks to be emptied and refilled with cold water on a regular basis. Ordinary injectors will not work with hot water (until hot-water injectors were developed) so condensing locomotives were usually fitted with axle-driven boiler feedwater pumps. When not working in tunnels, the steam was directed to the blast pipe and up the chimney in the usual way.
caption: Metropolitan Railway A Class Note the large valves in the steam return pipes, switching between condensing and non-condensing modes.
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