Atmospheric railway

Several variants of the principle were proposed in the early 19th century, and a number of practical forms were implemented, but all were overcome by unforeseen disadvantages and discontinued within a few years.

In 1799, George Medhurst of London discussed the idea of moving goods pneumatically through cast iron pipes, and in 1812, he proposed blowing passenger carriages through a tunnel.

In his treatise, described below, Samuda implies that the pipe would be used in one direction only, and the fact that only one pumping station was erected suggests that trains were gravitated back to the lower end of the run after the atmospheric ascent, as was later done on the Dalkey line (below).

A piston, which is introduced into this pipe, is attached to the leading carriage in each train, through a lateral opening, and is made to travel forward by means of the exhaustion created in front of it.

The continuous pipe is fixed between the rails and bolted to the sleepers which carry them; the inside of the tube is unbored, but lined or coated with tallow 1/10th of an inch thick, to equalize the surface and prevent any unnecessary friction from the passage of the travelling piston through it.The operation of the closure valve was to be critical: Along the upper surface of the pipe is a continuous slit or groove about two inches wide.

As this was the first commercially operating atmospheric railway, it attracted the attention of many eminent engineers of the day, including Isambard Kingdom Brunel, Robert Stephenson, and Sir William Cubitt.

[3][6][9] It was through his interest that the Pereire brothers decided to adopt the system for an extension to Saint Germain itself, and construction started in 1845, with a wooden bridge crossing the Seine followed by a twenty-arch masonry viaduct and two tunnels under the castle.

The pressure in the air cauldron (claudieres) attached to the exhausting machines is equal to six absolute atmospheres.He described the valve: Throughout the entire length of the tube, a section is made in the top, leaving an open space of about five inches.

[note 4] A two-needle electric telegraph system was installed on the line, enabling station staff to indicate to the remote engine house that a train was ready to start.

On quitting the station on locomotive lines we have frequently experienced a "jerk" amounting at times to an absolute "shock" and sufficient to alarm the nervous and timid passenger.

At this time the directors were making plans for the Epsom extension; they quickly revised their intended purchase of engines from Maudslay, and invited tenders; Boulton and Watt of Birmingham were awarded the contract, their price having been considerably less than their competitors'.

As for the tallow-and-beeswax compound that was supposed to seal the joint after every train, Samuda had originally said "this composition is solid at the temperature of the atmosphere, and becomes fluid when heated a few degrees above it"[4] and the hot weather had that effect.

An 1859 source reports rats entering the iron tube overnight to eat the tallow, and "hundreds" being killed each morning when the pump was activated for the first train.

[16] Delays became frequent, due to inability to create enough vacuum to move the trains, and stoppages on the steep approach inclines at the flyover were commonplace, and widely reported in the press.

The winter of 1846/7 brought new meteorological difficulties: unusually cold weather made the leather flap stiff, and snow got into the tube[note 9] resulting in more cancellations of the atmospheric service.

The reason seems not to have been made public at once, but the trigger seems to have been the insistence of the Board of Trade inspector on a second junction at the divergence of the Brighton and Epsom lines.

Interested parties in Devonshire considered it important to extend the connection to Plymouth, but the terrain posed considerable difficulties: there was high ground with no easy route through.

If Brunel had decided definitely to use the atmospheric system at the planning stage, it would have allowed him to strike a route that would have been impossible with the locomotive technology of the day.

Commentators often blame this on it being designed for atmospheric traction; for example: Sekon, describing the topography of the line, says that beyond Newton Abbot, the conformation of the country is very unsuitable for the purpose of constructing a railway with good gradients.

Delivery of the machinery and laying of the pipes was much delayed, but on 11 August 1846, with that work still in progress, a contract was let for the engines required over the hilly section beyond Newton.

This would not have rectified the immediate problem, and complete replacement of the leather flap was required; this was estimated to cost £32,000—a very large sum of money then—and Samuda declined to act.

Maintenance of the traction pipe and the valve was Samuda's contractual responsibility, but Brunel indicated that he was blaming the company for careless storage, and for the fact that the valve had been installed for some time before being used by trains; Brunel declined to go into the liability question, alluding to possible palliative measures, but concluded: The cost of construction has far exceeded our expectations, and the difficulty of working a system so totally different from that to which everybody—traveller as well as workmen—is accustomed, have (sic) proved too great; and therefore, although, no doubt, after some further trial, great reductions may be made in the cost of working the portion now laid, I cannot anticipate the possibility of any inducement to continue the system beyond Newton.

Lengthy technical discussion took place, in which Gill stated that Clark and Varley were prepared to contract to complete the atmospheric system and maintain it over a section of the line.

The section put into service, Le Pecq to Saint Germain, was almost exactly the same length as the Dalkey line, and was operated in a similar way except that the descent by gravity was made with the piston in the tube so that air pressure helped retard speed.

As well as a brake, the driver had a by-pass valve which admitted air to the partially exhausted traction tube ahead of the piston, reducing the tractive force exerted.

Clayton describes it: the change could be controlled by the driver while in motion; a lever operated a device rather like an umbrella at the rear of the piston head; it had hinged steel ribs.

In fact this was never used on the South Devon Railway, for the 22-inch tubes there were never opened; and the change at Forest Hill only lasted four months before the end of the atmospheric system there.

Electric power for lighting and braking is supplied to the train by a low voltage (50 V) current through the track the vehicles run on; this is used to charge onboard batteries.

In 2019 the government of Ghana signed a build–operate–transfer concession agreement with a South African consortium to develop the project, at an estimated cost of $2.6 billion dollars.

in the United States has developed the concept of a high-speed atmospheric train that uses vacuum and air pressure to move passenger modules along an elevated guideway.