Adjacent to the broad gauge running line is a display on Brunel's ill-fated attempt at ‘atmospheric’ propulsion. The three 22” diameter cast iron pipes are a relic of I K Brunel’s flirtation with atmospheric traction on the South Devon Railway. The tubes were discovered, by the Great Western Society, being used for drainage at Goodrington in Devon and are displayed on broad gauge baulk road at the 1 in 36 gradient of Dainton Bank, the steepest part of the line for which they were intended.
The South Devon Railway was persuaded by Brunel to adopt Clegg & Samuda’s system of atmospheric traction. This consisted of stationary pumping engines creating a partial vacuum in large slotted cast iron pipes laid between the rails. The pipe was sealed by airtight valves at each end and a metal strip hinged by leather along the length of the slot. The partial vacuum allowed a piston attached to a carriage to be propelled by the greater pressure of the atmosphere behind. This system was intended to be capable of operating trains on much steeper gradients and sharper curves than locomotives could manage.
The largely flat section of the Railway between Exeter and Newton (Abbot), including the scenic seawall section, was duly built with 15” pipes for atmospheric operation, experimental services beginning in September 1847 and full atmospheric operation commencing in February 1848.
The 22” pipes, such as those on display, were intended for the steeply graded section between Newton and Totnes where the larger diameter was needed for greater tractive effort. However as this section was being built the system’s failings were becoming evident. The leather hinges were inadequate and air leaked into the pipes overworking the undersized pumps. The 1848 accounts show that atmospheric working cost 3s1d (15.5p) a mile compared to 1s4d (7p) for locomotive working.
Atmospheric working between Exeter and Newton was discontinued from 10 September 1848 (after only 7 months). The Newton to Totnes section was never opened for atmospheric traction, though an engine house was built at Dainton, and pipes were laid from Newton as far as Dart Bridge in Totnes.
The steep grades and sharp curves of this part of the line have remained, as a legacy of Brunel’s ‘Atmospheric Caper’, to provide a challenge to Great Western locomotives and their successors as they struggle to lift their heavy trains over the South Devon banks.