Everything about Atmospheric Railway totally explained
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's an arrangement for admitting air to the tube behind the piston so that
atmospheric pressure propels it (and the train to which it's attached) forward.
Historical applications
Commercial applications of the system were as follows:
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.
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 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.
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 isn't 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, 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 wasn't 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
.
Recent applications
The
Aeromovel Corporation markets an automated people mover that's 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).
Technical considerations
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 wasn't 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.Further Information
Get more info on 'Atmospheric Railway'.
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