Atmospheric railway

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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^[1].

Arriving at Kingstown, The Illustrated London News, 1844

An atmospheric railway is a railway that uses air pressure to provide power for propulsion. 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.^[2]

[edit] Historical applications

Commercial applications of the system were as follows:

• The Birmingham, Bristol & Thames Junction Railway (0.5 mi (1 km)) Trial in 1840^[3]
  
• The Dalkey Atmospheric Railway extension of the Dublin and Kingstown Railway between Kingstown (Dún Laoghaire) and Dalkey, Ireland (1.75 mi (3 km)) 1844-54^[4]
• The London and Croydon Railway between Croydon and New Cross, London, England (7.5 mi (12 km)) 1846-47
• Isambard Kingdom Brunel's South Devon Railway between Exeter and Newton Abbot, England (20 mi (32 km)) 1847-48
• The Paris–Saint-Germain railway between Bois de Vésinet and Saint-Germain-en-Laye, France (8.5 km (5 mi)) 1847-60 ^[5]
• Beach Pneumatic Transit

The Crystal Palace atmospheric railway of 1864 had seals around the carriage, so (like Rammell's similar GPO Railway) the whole carriage fits in a tube tunnel and was propelled by the large fixed fan.

[edit] South Devon Railway

The remains of the SDR's atmospheric railway pipe at Didcot

Main article: South Devon Railway engine houses

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.^[6]

The section from Exeter to Newton (now Newton Abbot) was completed on the principle, with stationary engines spaced at around 3 miles (4.8 km) intervals. Trains ran at speeds of up to 70 mph (112 km/h), but service speeds were usually around 40 mph (64 km/h).^[7] The level portions used 15 inches (381 mm) pipes but the steeper gradients west of Newton were to have used 22 inches (559 mm)pipes. It is not clear how the change between the two pipe sizes would have been achieved unless the piston carriages were changed at Newton. It is also unclear how the level crossing at Turf was operated as the pipe projected some way above the rails.

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.

Pumping House at Torquay, Devon

Atmospheric-powered service lasted less than a year, from 1847 (experimental services began in September; operationally from February 1848) to 9 September 1848. 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.

[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] Technical considerations

Illustration from A Treatise on the Adaptation of Atmospheric Pressure to the Purposes of Locomotion on Railways, Samuda

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 section above gives a case study of Samuda's system on the South Devon Railway 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:

• Shunting the trains into atmospheric formation was difficult or cumbersome (although this would have seemed less of a problem in an era when much shunting was in any case carried out by horse- or man-power)
• A change in traction, with consequent delays, would be necessary if an atmospheric line became part of a through route
• There had to be gaps in the atmospheric tubes at points, with flyovers or similar arrangements at junctions; and special arrangements would have been needed at level crossings.

[edit] References

[edit] Further reading

• Clayton, Howard (1966). The Atmospheric Railways. Lichfield: Howard Clayton. 
• Hadfield, Charles (1967). Atmospheric Railways, 1st edn, Newton Abbot: David & Charles. ISBN 0-7153-4107-3. 

[edit] See also

• Dalkey Atmospheric Railway
• Beach Pneumatic Transit
• Crystal Palace pneumatic railway
• 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
• Steam catapult - the arrangement of seal and traveller is essentially the same, albeit all steel.
• Vactrain - combination of gravity and air power