Atmospheric railway
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Image:Brunel's Atmospheric Railway.jpgAn atmospheric railway is a railway in which air pressure or vacuum is used to drive trains. The first commercial application of the system was the line from Kingstown (Dún Laoghaire) to Dalkey in Ireland. This system was also used by Isambard Kingdom Brunel in the 19th century on a 52-mile section of the South Devon Railway between Exeter and Plymouth, England and on the London & Croydon Railway in 1845, but was soon abandoned.
The supposed advantage of the atmospheric system was its hillclimbing ability, but Brunel chose to test the system on a relatively flat section. Brunel simply assumed that the system would work, because the mainline to Cornwall was designed to contain some very challenging gradients of up to 1 in 38.
The atmospheric system did not work, for the following reasons:
- Failure of the tube seals, likely due to rats eating the leather sealing strip greased with tallow.
- Shunting the trains into atmospheric formation was difficult or cumbersome.
- The pump stations every few kilometres had to be continuously run and were expensive to operate.
- The hillclimbing abilities of the system were not adequately tested.
- It was not clear how atmospheric railway tubes could be compatible with railway points.
- Telegraphy may not have been advanced enough to co-ordinate the pump stations and trains properly.
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[edit] Brunel's "atmospheric caper"
The extension of Isambard Kingdom Brunel's broad gauge railway westward from Exeter towards Plymouth by the South Devon Railway Company was one of his interesting though ultimately unsuccessful technical innovations. Instead of using locomotives, the trains were moved by Clegg and Samuda's patent system of atmospheric (vacuum) traction, whereby stationary pumping engines sucked air from a pipe laid between the rails, the trains being moved by a piston running in this pipe and connected to the underside of a carriage.
The section from Exeter to Newton (now Newton Abbot) was completed on this principle, with stationary engines spaced every two miles, and trains ran at approximately 20 miles per hour (32 km/h)<ref name=3ships>Dumpleton. Brunel's Three Ships, Intellect Books, 2002. ISBN 1-84150-800-4</ref>. Fifteen-inch (381 mm) pipes were used on the level portions, and 22-inch (559 mm) pipes were intended for the steeper gradients west of Newton. Unfortunately, the technology required the use of leather flaps to seal the vacuum pipes. In view of the harsh environment of the line, which runs directly adjacent to the sea and is soaked with salt spray in even moderate winds, the leather had to be kept supple by the use of tallow, which is attractive to rats; the result was inevitable – the flaps were eaten, and air leaked in, destroying the vacuum.
Atmospheric-powered service lasted less than a year, from 1847 (experimental services began in September; operationally from February 1848) to September 10 1848<ref>Parkin, Jim. Engineering Judgement and Risk, Thomas Telford (publishers), 2000. ISBN 0-7277-2873-3</ref>. The accounts of the SDR for 1848 suggest that the atmospheric traction cost 3s 1d per mile (£0.10/km) compared to 1s 4d (£0.04/km) for conventional steam power. Part of the problem was that the engines had to be run for longer than expected as they were not, at first, connected to the telegraph and so had to pump according to the railway timetable, until the train passed. As a result, many trains ran very late.
The system was never expanded beyond Newton, although several of the engine houses were built. Similarly, the proposal to use the same system on the Cornwall Railway was not pursued.
There are remains of several South Devon Railway engine houses, including that at Starcross, on the estuary of the River Exe. It is a striking landmark and a reminder of the atmospheric railway – which is also commemorated in the name of the village pub. A section of the pipe, without the leather covers, is preserved in Didcot Railway Centre.
[edit] Recent Applications
The Aeromovel® Corporation markets an automated people mover which is air driven. The light-weight trains ride on an elevated concrete box girder which houses electrical motors that drive air inside the box girder, creating a constant air flow. Each train car has a square plate protruding into the box girder. The plate acts as a sail and can be rotated into the air flow to catch the wind and accelerate the car. Systems have been built in Porto Alegre, Brazil (a two-station demonstration line) and Taman Mini Indonesia Indah, Jakarta, Indonesia (a 2-mile, 6-station loop serving a theme-park).
[edit] See also
- Cable railway - a more successful albeit slow way of overcoming steep grades.
- Funicular - A system of overcoming steep grades using the force of gravity on downbound cars to raise upbound cars.
- Pneumatic tube
- Steam catapult - the arrangement of seal and traveller is essentially the same, albeit all steel.
- Dalkey Atmospheric Railway
[edit] References
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