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Jolly-sailor station on the London and Croydon Railway in 1845, showing the atmospheric-propulsion system pumping station, with its Gothic chimney/exhaust vent. Note the locomotive-less train"Jolly-sailor Station", The Pictorial Times, 1845.
An atmospheric railway is a railway that uses air pressure to provide power for traction. A pneumatic tube is laid between the rails, with a piston running in it suspended from the train through a sealable slot in the top of the tube. By means of stationary pumping engines along the route, air is exhausted from the tube leaving a vacuum in advance of the piston, and there is an arrangement for admitting air to the tube behind the piston so that atmospheric pressure propels it (and the train to which it is attached) forward.This system is generally attributed to Clegg and Samuda. For instance, see this site (retrieved 2007-11-24) which also includes drawings of the internals of the system.
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Commercial applications of the system were as follows:
A supposed advantage of the atmospheric system was its hillclimbing ability. On the two longest-lived applications, at Dalkey and Saint-Germain, this seems to have been vindicated: here the system was used on uphill journeys and gravity in the other direction. Brunel assumed that the system would work on the very challenging gradients of up to 1 in 38 on the Plymouth mainline if the South Devon application had been extended beyond Newton, probably by increasing the diameter of the tube on the gradients (although this would have involved a complex expanding piston arrangement); however here it was tested only on a relatively flat section.
The following section gives a case study of the South Devon application which outlines some of the technical problems, of which maintaining an adequate seal to the tubes, given the technology of the 1840s, was a serious one. Other reasons why it was not practicable on a large scale are more related to operational difficulties:
The extension of 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 uses of technical innovations. Brunel and others from the GWR traveled to Ireland to view such a system first hand. There, Brunel\'s engineer of locomotives for the GWR, Daniel Gooch, calculated that conventional locomotives could work the proposed line at lower cost, but Brunel\'s concerns with the heavy grades led him to try the system regardless.Awdry, Christopher. Brunel\'s Broad Gauge Railway, 1992, ISBN 0-86093-504-3, p.49
The remains of Brunel\'s atmospheric railway at Didcot Railway Centre
The section from Exeter to Newton (now Newton Abbot) was completed on the principle, with stationary engines spaced every two miles, and trains ran at approximately 20 miles per hour (32 km/h)Dumpleton, Bernard (2002). Brunel\'s Three Ships. Bristol: Intellect Books. ISBN 1-84150-800-4. . The level portions used fifteen-inch (381-mm) pipes and the steeper gradients west of Newton used 22-inch (559-mm). The harsh environment of the line, which runs directly adjacent to the sea and is soaked with salt spray in even moderate winds, presented difficulties in maintaining the leather flaps provided to seal the vacuum pipes, which had to be kept supple by being greased with tallow; even so, air leaked in, destroying the vacuum. (The idea that the tallow was particularly attractive to rats which chewed the seal is without contemporary foundation.) Many trains ran very late.
Atmospheric-powered service lasted less than a year, from 1847 (experimental services began in September; operationally from February 1848) to September 10 1848Parkin, Jim (2000). Engineering Judgement and Risk. London: Thomas Telford (publishers). ISBN 0-7277-2873-3. . 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, which increased pumping costs.
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.
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).
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