Maintenance of the leather valve was the nail in the coffin, though. As with the Croydon line, a metal plate intended to cover the leather valve to protect it from the elements wasn't installed, despite it being part of Samuda's design. The leather was prone to freezing during the winter of 1847-48, and drying out from the sea air and heat of the following summer. It had to be treated to keep it supple, and repaired at great expense. Debris was a constant threat, and there is some anecdotal evidence rats were attracted to the tallow sealant and leather, eating it away to cause further damage.
Samuda had been employed to maintain the line, but ultimately the entire leather valve needed replacing, which was the straw that broke the camel's back. It would have been an extremely costly undertaking, and Samuda refused. The question of liability bounced between Brunel, Samuda and the South Devon Railway Company as the atmospheric system fell into disrepair. Though a telegraph became operational in August 1848, significantly reducing coal consumption at the pumping stations, in early September the atmospheric line was abandoned and replaced by steam locomotives. A shareholder meeting was held in January 1849 to make the final call. Some were keen to continue the service, but in the end votes against outnumbered votes in favor by nearly five to one.
Despite the failures of the London and South Devon projects, the much shorter atmospheric lines in Ireland and France ran more or less uninterrupted for over a decade until more powerful steam trains capable of the ascents replaced them. In that sense, atmospheric railways were a stopgap technology. They were favorable to early steam engines, but were eventually outpaced by those same machines as they improved over the decades.
The draw of atmospheric transport didn't die with Brunel's overambitious "caper." Having already built a pneumatic system for the transport of letters and other goods around the capital, engineer Thomas Webster Rammell built a short demonstration line in south London's Crystal Palace Park in 1864, which was operational for a few months. This was a subway style atmospheric system where the whole car was propelled down a tunnel by a large fan, and pulled the other way by reversing the rotation of the blades to create a partial vacuum. It's thought this was intended to prove the design could work for a short, underground line running beneath the River Thames between London's Waterloo station and Whitehall. Construction of this, overseen by engineer Edmund Wragge, began in 1865 but was never completed due to a financial crisis that struck the following year.
Not long after, inventor Alfred Ely Beach set to work on the first underground transportation system in New York City. Funding the project in part with his own money, he completed construction of a block-long tunnel under Broadway in less than two months. The Beach Pneumatic Transit line worked in the same way as the Crystal Palace demonstration, blowing and sucking cars along its length. In early 1870 it opened to the public, who could buy a return trip ticket -- there was no exit at the end of the tunnel, just a dead end -- for 25 cents. It never amounted to much more than a novelty, though. The plan was to extend the subway by roughly five miles to Central Park, but bureaucracy and a lack of funding and support led to it closing down in 1873, despite Beach having finally obtained the permission he needed. It did, however, give rise to a pneumatic mail transport system in the city.
After Beach's failed attempt to build a pneumatic subway system, appetites waned. It's important to note here that Hyperloop and similar concepts don't use air pressure (or the lack thereof) as a means of power. The evacuated tunnels integral to their design are simply to reduce drag on the vehicle.