At the very end, about a current implementation:<p>> <i>The free piston is magnetically coupled to the passenger modules above; this arrangement allows the power tube to be closed, avoiding leakage. The transportation unit operates above the power tube on a pair of parallel steel rails. The company currently has a 1/6 scale pilot model operating on an outdoor test guideway... The Corporation claims that a full-scale implementation would be capable of speeds in excess of 200 mph (322 km/h).</i><p>It sounds like magnetic coupling is the solution to the maintenance issues.<p>But it also seems like you can only have one train on a track at any given time.<p>Or, at least a track would have to be divided into sections, each with its own pumps and own piston, which could only support one train at a time... and then the piston would have to be sent backwards to the beginning of the section to be ready for the next train. (And you'd need electromagnets to let go of one piston and grab the one on the next section.)<p>So I can see why this might not be viable for something like a city's subway system.<p>But at the end of the day... what advantages would this ever have over electric trains that get their power from a third rail?
<a href="https://en.wikipedia.org/wiki/Dalkey_Atmospheric_Railway" rel="nofollow">https://en.wikipedia.org/wiki/Dalkey_Atmospheric_Railway</a><p>"The journey to Dalkey could be completed in just over 3 minutes with the speed being limited by the need to brake for curves on the"<p>That's faster than the train gets there today.
Related technology: <a href="https://en.wikipedia.org/wiki/Fireless_locomotive" rel="nofollow">https://en.wikipedia.org/wiki/Fireless_locomotive</a>
I did not know that a modern version of the system was in use. Spent a few years living along the South Devon route, and Brunel's seals eaten by rats were a definite thing.