How did it work?
Atmospheric Model in GWR Room
Well, the Atomspheric system made use of atmospheric pressure to propel rolling stock. In the system adopted by the South Devon Railway, a large diameter tube was laid between the rails. This was connected to a series of pumping engines, which were able to evacuate the air ftrom the pipe. Running along the top of the pipe there was a silt, which had a leather flap attached to one side. This closed over the slit and allowed a vacuum to be created in the pipe.
Slung under the first vehicle of the train was a piston which fitted snugly into the pipe; the connection from the piston to the vehicle being made through the slit in the pipe. Prior to the train leaving, the air was pumped out of the pipe ahead of the train (in advance of the direction of travel). Air at atmospheric pressure was then admitted to the pipe behind the piston and the train was propelled forward by this pressure.
Starting trains from stations was difficult, and small auxillary pipes were provided with rope attached to small pistons. The ropes were coupled to the front of the piston carriage and used to assist the starting of the train being disconnected once the train was in motion.
Newton Abbot pumping house
With no heavy locomotives the permanent way (foundation track) could be of light construction and hense cheaper to build.
Trains were quieter and cleaner as there was no smoke or cinders from locomotives.
In theory accidents were unlikely, as trains could not travel in opposite directions on the same track at the same time.
Trains often overshot the platform as this stopping manouver proved extremely difficult.
Communication was required between the stations and the pumping houses so that the pumps could start evacuating the pipe in advance of the train leaving.
It was not possible to use the pipe where lines diverged or met, e.g. points and junctions. The train had to "coast" over their sections of track.