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Railway Signalling |
 Grosmont Signal Box |
We are all familiar with the Signal Box that used to grace every
station and wayside junction on our Railways. While the simple idea of just pulling levers to clear the signals is basically correct the actual function is a little more complex. The Signalman and the mechanism in the Signal Box are the safety system that prevents accidents and controls the running of the trains to the timetable. While the system is controlled by a set of very strict rules, mechanical interlocks are built into the Signal Box that physically prevent the signalman from setting what are known as 'Conflicting Routes'. |
| Consider the situation shown opposite:- With the points 'Normal' as shown in the diagram, Signal 1 must NOT be cleared as any train approaching from the left on that line could be de-railed. On the other hand Signal 2 Can be safely cleared to allow a train to pass. If the Points need to be reversed then both signals need to be at danger then Signal 1 can be safely cleared. A simple mechanical interlocking using notches and locking 'Tappets' was used to provide this function. The diagrams below show a simple tappet locked three lever frame controlling the point and signals. On the right is a diagram of the locking levers mechanism showing the lever tails with the notches and the tappets connected to the locking bars, while on the other side is a representation of the signal levers. Click on the levers to change then an see how the the interlocking works. |
 Trailing Junction |
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In the Next Part of the description we will see how mechanical and electrical aids have been used to help the signalman
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