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Atmospheric railway
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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.
799 George Medhurst of London discussed the idea of moving goods, pneumatically, through cast iron pipes, and in 1812, he proposed, but never implemented, blowing passenger carriages through a tunnel.
In 1835 Henry Pinkus launched a prospectus for the National Pneumatic Railway Association.
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Encyclopedia
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.
Historical applications
In 1799 George Medhurst of London discussed the idea of moving goods, pneumatically, through cast iron pipes, and in 1812, he proposed, but never implemented, blowing passenger carriages through a tunnel.
In 1835 Henry Pinkus launched a prospectus for the National Pneumatic Railway Association. However it was not until 1838, when the gas engineer Samuel Clegg and the marine engineers Jacob and Joseph Samuda jointly took out a patent “for a new improvement in valves” that atmospheric propulsion became possible. The partnership set up a working model at the Samuda Brothers’ workshop in Southwark in 1839, and a demonstration track of the Birmingham, Bristol & Thames Junction Railway at Wormwood Scrubs between 1840 and 1843. The following year Joseph d'Aguilar Samuda published A Treatise on the Adaptation of Atmospheric Pressure to the Purposes of Locomotion on Railways
The Clegg-Samuda system attracted the attention and support of some of the foremost railway engineers of the day, notably William Cubitt, Charles Vignoles, and Isambard Kingdom Brunel, each of whom was engaged on the construction of new railway lines. It was also severely criticised by other engineers and railway commentators, notably Robert Stephenson and John Herapath.
Dalkey Atmospheric Railway
The first practical use of the system was the Dublin and Kingstown Railway's Dalkey Atmospheric Railway between Kingstown (Dún Laoghaire) and Dalkey, Ireland This line was built by Vignoles and operated between 1844 and 1854.
London and Croydon Railway
Cubbit recommended the system for the London and Croydon Railway between London Bridge station and Croydon. Clegg and Samuda were invited by the directors to supply equipment to operate their trains between London Bridge and Epsom. The first stage of this project (between Croydon and Forest Hill) opened in January 1846, but the system of propulsion encountered many problems with both the pumping equipment and in maintaining air-tight seals in the delivery pipes. The London and Croydon Railway became a part of the London Brighton and South Coast Railway in July 1846 and the new board of directors invited Samuda to operate the new atmospheric railway on their behalf in return for a fixed fee. However, once further propulsion problems became apparent in the second section of line to be equipped (between Forest Hill and New Cross) during 1847 the atmospheric method of propulsion was abandoned and the equipment sold.
South Devon Railway
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 innovation. Brunel and others from the GWR travelled to Ireland to view the atmospheric system at Dalkey first hand. Afterwards Brunel's engineer of locomotives for the GWR, Daniel Gooch, calculated that conventional locomotives could work the proposed Plymouth line at lower cost, but Brunel's concerns with the heavy grades led him to try the atmospheric system regardless.
The section from Exeter to Newton (now Newton Abbot) was completed on the principle, with stationary engines spaced at around intervals. Trains ran at speeds of up to 70 mph (112 km/h), but service speeds were usually around 40 mph (64 km/h). The level portions used pipes but the steeper gradients west of Newton were to have used 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.
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 initially 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 .
Other early applications
The Paris–Saint-Germain railway between Bois de Vésinet and Saint-Germain-en-Laye, France 1847-60
Beach Pneumatic Transit One city block long subway beneath Broadway in New York City, USA 1870 - 1873.
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.
Recent applications
The 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).
A web page describing a system called 'Whoosh' was available for a time. Basically the system is a single monorail track of the vacuum tube with a track either side. The piston in the tube is connected to the carriage below which is supported by wheels running on the tracks each side of the tube.
Technical considerations
Advantages
The supporters of the atmospheric system claimed it had several advantages over traditional motive power by steam locomotive.
- 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.
- Operating efficiencies. Atmospheric railways could be operated on cheaper and lighter tracks which did not have to carry the weight of a locomotive, and could take advantage of sharper curves.
- Fuel efficiency. It was far cheaper to maintain and operate a few large pumping engines than a large number of individual locomotives.
- Cleanliness. The smoke and dirt from the steam engines was kept away from the passengers.
- Safety. The system could achieve higher speeds, but it would be impossible to operate two trains on the same stretch of track simultaneously and so collisions would be avoided.
Disadvantages
The ultimate failure of the system was due to technical problems with the stationary engines and the leather seals on the vacuum pipes. The former were suffered by the London and Croydon Railway but would have been overcome with more experience by the manufacturers and operators. The difficulty of maintaining an air tight seal in the vacuum pipes was a serious problem, particularly for the South Devon Railway Company that was never satisfactorily solved using the materials and technology of the 1840s.
However, the atmospheric system also suffered from a number of operating problems.
- 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.
Overall assessment
The atmospheric system foresaw the inherent efficiencies of delivering centrally generated power to the line side rather generating it on individual locomotives, as would ultimately become the normal practice with electrification systems. The use of modern materials and technology would overcome many of the problems of the original systems, but atmospheric railways were ultimately too inflexible for widespread use.
Further reading
See also
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