Originally posted by donga666
Originally posted by tidoco2222
Aaaawwww not the leaves on the line business I can write a very boring essay on that one.
Go on then
Ok you asked for it,
Railway signalling is operated by track circuits these circuits are put through the rails in most cases as low voltage DC tracks separated by insulated rail joints IRJ\'s.
These circuits in turn operate relays which are in essence very fancy switches and they are either energised or de-energised up or down.
The Track circuit is then eventually indicated on a signalman\'s panel at the controlling signal box in your case Andy York IECC (Intergrated Electrical Control Center).
The indication takes the form of lights on the diagram which is a basic plan view of the signalling layout for that area. If the Red lights are on then the circuit is occupied, relay de-energised/down thus the signalman will know that either a train is present on the track as the trains axles will short circuit the track circuit and therefore cut the supply to the track relay or there is a fault causing the track to show occupied. If the lights are out the track circuit is un- occupied, relay energised/up no train present and the line is therefore clear. If the track is occupied the track relay being down will interact with other relays in the signalling system and the signal in rear of the occupied track will go to danger (red) and remain so until the track circuit is clear.
Now the leaves on the line problem comes in during late autmn early winter when the trees are shedding their leaves. These leaves fall onto the line and start to rot the act of nature.
The mould generated by rotting leaves can cause an insulating paste to form on the railhead and in the most severe cases and can build up to such a degree that a train passing over this paste would fail to opereate the track circuit ie the wheels would not be able to short out the track circuit and therefore the track circuit would show clear with a train present and the protecting signal in rear would still show green ( what is commonly called a wrong side failure unprotected.) Which is the one of the most dangerous faults that can occur on the railway.
Told you it was boring I have simplified it somewhat but I am sure you get the gist.
