Isambard Kingdom Brunel - Brunel's "atmospheric Caper"

Brunel's "atmospheric Caper"

Though ultimately unsuccessful, another of Brunel's interesting use of technical innovations was the atmospheric railway, the extension of the Great Western Railway (GWR) southward from Exeter towards Plymouth, technically the South Devon Railway (SDR), though supported by the GWR. Instead of using locomotives, the trains were moved by Clegg and Samuda's patented system of atmospheric (vacuum) traction, whereby stationary pumps sucked air from a pipe placed in the centre of the track.

The section from Exeter to Newton (now Newton Abbot) was completed on this principle, and trains ran at approximately 68 miles per hour (109 km/h). Pumping stations with distinctive square chimneys were sited at two-mile intervals. Fifteen-inch (381 mm) pipes were used on the level portions, and 22-inch (559 mm) pipes were intended for the steeper gradients.

The technology required the use of leather flaps to seal the vacuum pipes. The natural oils were drawn out of the leather by the vacuum, making the leather vulnerable to water, rotting it and breaking the fibres when it froze. It had to be kept supple with tallow, which is attractive to rats. The flaps were eaten, and vacuum operation lasted less than a year, from 1847 (experimental service began in September; operations from February 1848) to 10 September 1848. It has been suggested that the whole project was an expensive flop. In Brunel's favour, it has been noted that he had the courage to call a halt to the venture instead of struggling on with it at greater cost.

The accounts of the SDR for 1848 suggest that atmospheric traction cost 3s 1d (three shillings and one penny) per mile compared to 1s 4d/mile for conventional steam power. A number of South Devon Railway engine houses still stand, including that at Totnes (scheduled as a grade II listed monument in 2007 to prevent its imminent demolition, even as Brunel's bicentenary celebrations were continuing) and at Starcross, on the estuary of the River Exe, which is a striking landmark, and a reminder of the atmospheric railway, also commemorated as the name of the village pub.

A section of the pipe, without the leather covers, is preserved at the Didcot Railway Centre.