Motive power depot, usually abbreviated to MPD, or railway depot is a term given to places where usually locomotives are housed when not being used, and also repaired and maintained. They were originally known as "running sheds", "engine sheds", or, for short, just sheds. Facilities are provided for refuelling and replenishing water, lubricating oil and grease and, for steam engines, disposal of the ash. There are often workshops for day to day repairs and maintenance, although locomotive building and major overhauls are usually carried out in the locomotive works.
MPDs in Britain are now often known as traction maintenance depots.
German practice
The equivalent of such depots in German-speaking countries is the Bahnbetriebswerk or Bw which has similar functions, with major repairs and overhauls being carried out at Ausbesserungswerke. The number of these reduced drastically on the changeover from steam to diesel and electric traction and most modern Bw in Germany are specialised depots, often responsible for a single rail class.
In thermodynamics, motive power is a natural agent, such as water or steam, wind or electricity, used to impart motion to machinery such as an engine. Motive power may also be a locomotive or a motor, which provides motive power to a system. Motive power may be thought of as a synonym for either "work", i.e. force times distance, or "power".
History
In 1679, physicist Denis Papin conceived the idea of using steam to power a piston and cylinder engine, by watching a steam release valve of a bone-digester rhythmically move up and down. In 1698, based on Papin’s designs, mechanical designer Thomas Savery built the first engine. The first scientific treatise on the energetics of engines was the 1824 book: Reflections on the Motive Power of Fire written by French physicist Sadi Carnot.
As an example, the Newcomen engine of 1711 was able to replace a team of 500 horses that had “powered” a wheel to pump water out of a mine, i.e. to “move” buckets of water vertically out of a mine. Hence, we have the precursory model to the term motive power. Based on this model, in 1832, Carnot defined work as “weight lifted through a height”, being the very same definition used to this day.
Motive power can refer to:
Motive Power is a bi-monthly railway related magazine that focuses on diesel locomotives in Australia. The first issue was published on 23 August 1998. Its headquarters is in Sydney. The content includes photographs of locomotives & trains, news about newly delivered and repainted locomotives, technical articles, and fleet listings of the various Australian railway operators. Articles about railway photography itself are sometimes included, as well as articles and advertisements about railway modelling.