Atmospheric Railway

Even though the 52-mile section between Exeter and Plymouth, England was only partly completed, Brunel's Atmospheric Railway was the most extensive ever built.

An Atmospheric Train passing the pumping house at Dawlish, Devon, 1887. Source unknown.

Another of Brunel’s interesting though ultimately unsuccessful technical innovations was the atmospheric railway, the extension of the 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 Cleggs and Samudas Patent system of atmospheric (vacuum) traction, the evacuation being done by stationary engines at a series of pumping stations. The section from Exeter to Newton (now Newton Abbot) was completed on this principle.

Known to locals as the “Atmospheric caper” it was plagued by problems from the start. Initial tests showed that the original 12" (30cm) pipe needed to be replaced by one of 15" (38cm). This meant that the pumping engines already installed along the route had to run faster than their design speed in order to exhaust the pipe sufficiently. The first passenger trains eventually ran in September 1847. There were frequent breakdowns, which resulted in third class passengers having to get out and push. The main problem though, was the leather sealing valve, which rapidly deteriorated. Unfortunately the technology required the use of leather flaps to seal the air pipes, the leather had to be kept supple by the use of tallow, and tallow is attractive to rats; the result was inevitable, and air-powered vacuum service lasted less than a year, from 1847 (experimental services began in September; operationally from February 1848) to September 10th 1848. The accounts of the SDR for 1848 suggest that the atmospheric traction cost 3s 1d per mile, compared to 1s 4d for conventional steam power.

Atmospheric Railway Map.

The pipes were cast too roughly, the steam engine pumps kept breaking down, and the leather valve along the pipe, was eaten by rats. Despite these problems, the Atmospheric Railway ran quite well towards the end of its life, and was a firm favourite with the passengers - except maybe those in third class. During the Spring and Summer of 1848 nine trains a day were running between Exeter and Teignmouth and average speeds of 64 mph (103 kph) were attained. The highest speed recorded was 70 mph (112 kph) with a train of 28 tons (28,450kg). When it was discovered that the whole valve needed replacing after less than a year of service at a cost of £25,000, the South Devon Railway directors abandoned the project in favour of conventional locomotives. The last atmospheric passenger train ran in September 1848.

The map shows the section of the South Devon Railway on which Brunel applied the Atmospheric System. Steam powered pumps were installed in engine houses at the places marked in red. Each engine house contained two 41.5 h.p (31 kW) vertical vacuum pumping engines fed with steam from boilers at 40lbs/square inch. (2.8 bar). They were designed to run independently to allow maintenance, though in practice they had to run coupled, and at top speed -to the dismay of the boilermen who had to keep shoveling the coal - in order to compensate for the leaky leather valve. The distance between successive pumping stations was around 3 miles (4.8km). Additional pumping houses were built at Torquay and Totnes, though engines were never installed. Brunel admitted his failure and took responsibility. He also took no fee for his work, setting a good professional example.

The pumping house at Starcross.

The pumping station at Starcross, on the estuary of the River Exe, remains as a striking landmark, and a reminder of the atmospheric railway — which is also commemorated in the name of the village pub. It was built in an Italianate style that was popular at the time. The two engines used to stand about 30 feet high in the main part of the building though they have long since disappeared. The top of the chimney was removed as it presented a danger to the main railway line that runs along the top of the sea wall in the foreground. A section of the pipe, without the leather covers, is preserved in Didcot Railway Museum. The pumping house at Starcross is the most intact remaining and the building is now the property of Starcross fishing club.