Signalling: Why?
It's no secret that I have found a great deal of pleasure in talking with the frequent offenders of the 'Theory of General Minories' thread, one of the foremost contributors is @Harlequin, to whom I had the pleasure of sending some of the SECR stock from a prior layout attempt, via an ebay sale. He states an eloquent case in a completely unrelated Track Design & Layout Planning thread:
On 01/12/2021 at 03:55, Harlequin said:...“operational interest” ... is to operate prototypically correctly. Breaking the rules of the real railway makes operations too easy, less challenging and ultimately uninteresting because operation then boils down to driving something from A to B simply because you feel like it. Doing that repeatedly gets boring very quickly. So operating like the prototype gives some structure...Correct operation requires a correct track plan and correct signalling.
I think we have covered the track plan to a greater or lesser degree fairly well already in this entry. But we haven't spoken much about the other - and one thing I absolutely did not expect out of railway modelling was the interest I've found in signalling, interlocking and the operation thereof.
I'm sure many people are about to stop reading at the thought of signalling, but I think it is actually something of an unsung hero - you see, if you are to have correct signalling then your track plan will have had a certain degree of rigor applied to it. If you follow your signalling design, then you will by nature be operating authentically.
Block Signalling as a way to operate calmly
Think of the following scenario of an inbound train at Minories sans signals;
- your train pulls into a platform from one of your double track entry roads
- as it coasts to a stop the station pilot that was waiting on the other main line road catches up, couples up and pulls off the coaches, immediately pulling back and shunting them into an adjacent platform
- The pilot then uncouples and heads to the loco pocket again.
- The main line loco trundles up the platform and out back onto the mainline.
Perfectly adequate but completely un-prototypical, but with signals and block working:
- The FY signal box calls attention to the Slaithwaite box with a single beat, then 3-1 bells (is line clear for an ordinary passenger train?)
- The slaithwaite box reviews the timetable, notes the platform allocation, train length, etc. and sets the route to the relevant platform road via lever frame, noting that the signals cannot be cleared until the turnouts are set, any facing point locks are also set. This blocks any potentially conflicting moves (and also the signals related to them), finally the slaithwaite box then replies with the same 3-1 bell code to accept the inbound train, and moves block indicator to 'line clear', allowing the FY signal box to pull off its starter signal and the Slaithwaite box to pull off it's home signal.
- As the train passes the FY signal box, the signalman calls ahead 2 bells (train on line)
- The slaithwaite box sets repeats this back, setting the block indicator to 'train on line'. The FY box is now blocked from clearing his starter signal (i.e. sending more trains)
- After a few minutes, the slaithwate box observes the train arriving, and once past its home signal, the signal is re-set to danger and the signalman sends 2-1 (train out of (your) section) to the FY box.
- The FY signalman acknowledges this by repeating it, the slaithwaite box now sets the block indicator to 'normal', so the process can be started again for another incoming train.
- In the meantime, the train now at the platform is uncoupled by the loco crew while passengers disembark. The train brakes are now fully engaged with no vacuum.
- Another series of levers are pulled to orient the pointwork for the pilot locomotive to come out of the loco pocket onto the down main up to the limit of shunt, and a shunt signal is cleared for that to happen. The LNWR used calling-on signals from the 1870's, so this is cleared to permit the shunter to enter an occupied section, and the couples up to the rear of the carriages, including building up the vacuum for the brakes to be released.
- More lever twaddling and a subsidiary shunt signal on the platform starter post is cleared, and another shunt move is permitted to the limit of shunt board on the main line, and as the shunter pulls back, the train locomotive also drifts backwards up to the platform starter, in clear view of the signal box.
- A final lever flourish sets the route and signals for the pilot locomotive to deposit the carriages in another platform road, before returning to the loco pocket.
- The main line loco needs coal and water, so the Slaithwaite signalman calls to the FY signal box 2-3 (is the line clear for a light engine?) and the first few steps are repeated in reverse for the light engine to dissapear up the line to the engine shed.
I'm sure a cacophony of bells would drive even the most hardened operator to tears, so I am assuming a very soft tapper sound. The beauty of this system is that all the essential information for the exchange is provided: are you ready? what kind of train is it? are the points set correctly? Oh no, don't send another train - I'm still halfway through dealing with this one! In addition, the tempo of movement is kept leisurely and consistent - there is no speedrunning of the sequence.
Signalling for Slaithwaite Road
CJF in his book 'Model Railway Signalling' handily puts forward a suggested signalling plan for Minories:
Model Railways Signalling credit CJF
Slaithwaite Road obviously has an additional siding, this wil be controlled by the similar ground signal to No. 5 as noted above. Rather than a semaphore however, 4, 5 and 6 (the notional pilot loco spur) will be the LNWR Crewe 1881-pattern revolving type as pictured here :
Greenfield circa 1954 credit to @coachmann
Model Railways, June 1910 p185
Interlocking
Interlocking as described above is the process by which moving a lever in a signal box may lock or unlock other levers. For example, in the diagram below, signal 1 is a distant signal - it can only be pulled off if both signals 2 and 3 are already pulled off. While it is clear, it locks 2 and 3 in their off position as well. Signal 3 and 13 are mutually exclusive, and pulling Signal 3 locks 7 or 12 in whatever position they're in. 7 and 12 both lock Signal 2 (the down home). Therefore, it is not possible to clear the down main home or distant, while either the branch connection or the crossover to the down main are in use. You can follow the chain of cause and effect around here and it's fastincating:
Model Railways, June 1910 p186
The design of interlocking is also interesting - how to determine what blocks which movement and releases what others. It sounds straight forward, but it's not! The grouping of the levers is deliberate - note the down signals at one end, and the up signals at the other, with spare levers bracketing the up and down main turnouts away from the rest of them. Lots to figure out on that one!
Edited by Lacathedrale
- 1
- 1
24 Comments
Recommended Comments
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now