>Not quite true, there is a manual brake handle that can be used to lock or
>unlock them (But that is trivial) You are quire correct in that the system
>operates as a pressurised loop air (Was steam, but did not work well, as
>most steam engines only have 120PSI (Some of the French ones got up to
>around the 160 mark). If I recall the pressure is around 180psi in the
>Westinghouse system


Nope - std air pressure is 70 to 90PSI for freight, slightly more for
passenger.

Complete FAQ about airbrakes.
http://www.geocities.com/CapeCanaveral/Hangar/8788/brake2.html

To be intelligible, you should know that RR cars have a bit of 'slack'
between the couplings.
This allows the engineer to start one car moving at a time and do other
fancy tricks (the
engine's nowhere near strong enough to just hook to the train and drag it
all at once).
(all of this slightly less important with diesel engines, which can overload
their motors briefly).

Now check out what happens when you're switching on a downgrade and don't
bother hooking the cars air line to the engine.

http://www.rrhistorical-2.com/cwrr/Parlor/runaway/index.html

Fro those interested in electropneumatic braking:

http://www.kalmbach.com/trains/Archive/Nov96/Brake.html