Basic Signalling

Signals and Telegraph - real and prototype

Basic Signalling

Postby Clive » Sun Feb 06, 2011 1:09 am

Hi All

One aspect that always seems to be wrong with too many model railways is their operation. As a non-railwayman I find this a tad annoying so to a pro it must be frustrating to watch and in some cases bordering on hysterical. This is well expressed by David Millward in http://scalerail.phpbbhosts.co.uk/viewtopic.php?f=83&t=965#p8977.

There are many aspects of operation that many of us non railwaymen need to learn and incorporate into our modelling and the correct use of signals is one of them. There have been many articles in the model railway press about signalling, most written by signalmen or those interested in S & T. The number of times the bell codes used between boxes has been published is unbelievable compared to what I am going to try to explain. Bell codes are very useful if a layout has many signal boxes like the East Riding Finescale's Holcombe Brook and Tottington, not as I have seen where it is a branch line terminus "ding donging" to the fiddle yard with only one geezer operating the layout.

Back to my waffle, each signal has a meaning and relays instructions to the driver but is no good if the message is not correctly delivered. One thing that spoils many layouts is the placing of signals, the poor driver would have to have brakes that are responsive as a controller on an electric train set to be able to stop his train time. :)
Below is the first illustration of a book entitled "Railway Signalling and Communications", given to me by a chap who served as an apprentice with the LNER before WW2, so if it was good enough starting point for the LNER then it is for me.
typical station.png

The book starts off explaining that each signal box should have a stop (home) signal to protect the first fouling point. These are signals 2 on the up line and 12 on the down line. The fouling point does not have to be a real one like the cross over at this station but could be theoretical one such as the commencement of block overlap. A home signal can be cleared without the proceeding distant being cleared or the starting signal to allow operation within station limits to take place.
A distant signal is provided in each direction. This signal is placed a full breaking distance from the home signal, so should the driver of a train pass it at caution he has ample room which bring his train to a halt if the home signal is at danger. This signal cannot be cleared if the home or any subsequent stop signals are at danger.
Starting signals, numbers 3 and 11, are necessary for operating requirements. They enable movements like shunting to take place without the next box (box in advance) having to accept the train. Starting signals cannot be cleared without the box in advance accepting the train. Note that the starting signals are placed to allow the longest train to safely be placed between the signal and the last point that could be blocked by the train. See http://scalerail.phpbbhosts.co.uk/viewtopic.php?f=14&t=877&start=0&hilit=Freight+train+books for information about train lengths and were to find out what there were/are for your lengh of model railway.

Only the home signal can be cleared, allowing a train to proceed to the starting signal without being locked to the distant or the starting signal. The starting signal is locked by the box in advance, so unless the fiddle yard can take a train this will remain at stop. The distant can only be cleared if all the stop signals are cleared and is locked with both the home and starting signal. For a train passing through the station the first signal to be cleared will be the starting signal, followed by the home then the distant, the opposite way to which the train passes. Edit, whoops. The correct sequence should be home signal pulled first, followed by starter signal then the distant signal. Looking at many model railways the distance from home to the distant signal and from the last point to the starting signal would be far greater than most of us have room, therefore it would not look wrong to only have the home signals on a layout using the above track plan.

As a protecting signal the home signal cannot be cleared if any of the point work is reversed therefore needs to be locked with the points it protects. Conversely the shunting (ground) signals cannot be cleared until the points are reversed. Signals 4 and 8 can be cleared to allow reversing movement on the main lines but these would be locked to their respective home signals to prevent an opposing movement being signalled. As the book this was taken from is based on LNER practice there is only one ground signal at the position of signal 4. The LNER used one to indicate that the driver could shunt the train but did not indicate which route. Not all railways worked like this, for example the LMS would have a stack of four signals to indicate not only the driver could shunt but which route he was taking, so it is worth checking the local practice. With the respective points 5, 7, and 9 reversed the ground signals 6, 8 and 10 are unlocked and can be cleared to allow movement to the down line. If one of them is cleared it would lock signal 4 to prevent a conflicting movement.

I have mentioned that the signals and points would be locked to prevent a conflicting movement taking place. I am not going to go into how mechanical locking takes place because as modellers we can either do the locking mechanically, electrically or electronically or even remember that we cannot have signal 3 cleared if point 7 is reversed. The important thing is that we should ensure that we do not set up opposing movements.
Notice how the signals and points are numbered, these correspond to their position on the signal box frame. The up signals are placed at one end and the down signals the other, this makes life easier for the signalman and for the routing of the signal wires. The shunting signals and points are placed in the centre of the frame, and again this helps with the routing of the point rodding and signal wires along as well as helping the signalman. Having the levers in the frame the correct colours matching the signals and points and the signal wires and point rodding placed correctly help with the visual appearance of the layout and coupled with correct signalling operation could convince a railwayman that you know what you are doing.
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Clive Mortimore

Model, noun representation in 3 dimensions of existing person or thing or proposed structure esp. on smaller scale.....(Oxford dictionary)
Clive
 
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