Atmospheric railway
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An atmospheric railway is a railway that uses air pressure or vacuum to provide power for traction. The first commercial application of the system was the line between Kingstown (Dún Laoghaire) and Dalkey in Ireland (1844 - 1854). This system was also used by Isambard Kingdom Brunel on a 52-mile section of the South Devon Railway between Exeter and Plymouth and on the London & Croydon Railway in 1845. Both were soon abandoned.
Although the supposed advantage of the atmospheric system was its hillclimbing ability, Brunel only tested the system on a relatively flat section. He simply assumed that the system would work on the very challenging gradients of up to 1 in 38 on the Plymouth mainline.
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 pumping stations every few kilometres had to run for longer than expected to accommodate late-running trains, and were therefore expensive to operate.
- The hillclimbing abilities of the system were not adequately tested.
- There had to be gaps in the atmospheric tubes at points, and special arrangements at level crossings.
- Telegraphy may not have been advanced enough to properly co-ordinate the pump stations and trains.
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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 (SDR) 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 in this pipe which was 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)[2]. The level portions used fifteen-inch (381-mm) pipes and the steeper gradients west of Newton used 22-inch (559-mm). 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[3]. 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. Therefore, many trains ran very late.
Despite the building of several engine houses the system never expanded beyond Newton. 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 one at Starcross, on the estuary of the River Exe. It is a striking landmark and a reminder of the atmospheric railway – which the name of the village pub also commemorates. 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 that is air driven. The elevated lightweight trains ride on a concrete box girder containing electric motors that drive air inside the box girder, creating a constant airflow. Each train car has a square plate protruding into the box girder. The plate is rotated into the airflow to catch the wind and accelerate the car. Systems have been built in Porto Alegre, Brazil (a two-station demonstration line) and in 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
- ^ 1845, "Jolly-sailor Station", The Pictorial Times
- ^ Dumpleton. Brunel's Three Ships, Intellect Books, 2002. ISBN 1-84150-800-4
- ^ Parkin, Jim. Engineering Judgement and Risk, Thomas Telford (publishers), 2000. ISBN 0-7277-2873-3
