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Clearing subsidiary signals.


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  • RMweb Gold

>>>Yellow shunt signals are not used on running lines.....

 

Usually....:-)

 

There was one on the No 2 platform road at Cowes, and also one on the bay at the east end of Salisbury. In both cases they were in effect an alternative to a running-shunt. And was it not the case at one time on the LNER that they used yellow discs instead of running-shunts on running lines?

 

Ducks back behind parapet.... :O

Now that is very interesting Chris - Cowes shows up quite well on the online version of the SRS diagram and is, I think, a very unusual arrangement as signal 18 must inevitably have had to lock the release crossover (No.3) and be led by No4. (the FPL for No.3) which would, on the face of it render 22 superfluous.  So presumably its use was to enable a subsequent run round move from the Platform No.2 line via what was - for such a move - a facing crossover; fascinating stuff.   Link to SRS diagram -

 

http://www.s-r-s.org.uk/html/srs/R266.htm

 

I can't find a large scale drawing of Salisbury East on the 'net but the small scale SRS drawing shows, I suspect, exactly the place you mean with  - similar in effect to Cowes - what amounts to a facing release crossover in that bay.

 

I'm not sure about any LNER examples but what did happen as far as I have been able to ascertain is that many earlier types of what amounted to points indicators (albeit independently worked in many cases) were painted yellow in the Post Grouping period when the 'yellow disc' Rules were initially established.

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I have been enjoying reading the electronic copies of Railway "block" signalling : the principles of train signalling and apparatus for ensuring safety by Pigg, James Published [1899?] and The first principles of railway signalling including an account of the legislation in the United Kingdom affecting the working of railways and the provision of signalling and safety appliances, by C B Byles, 1910.

 

To be honest running shunts as such do not crack a mention Not that you would expect them to really). Pigg is adamant that shunting signals are 'stop' signals even if not "stop signals" like home signals etc. Byles makes the more modern distinction in line with the mid 30s rules. (per Rule 16). He distinguishes shunting signals from "running signals", which he describes them as being similar to.

 

Both are clear (forgive the pun) that for a stop signal to be lowered the line must be 'clear' or 'free from obstruction', and the way must be set.

 

Byles notes that for a distant signal to be off the home signal and all other "running signals" be off too throughout the block.

 

Regards

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  • RMweb Gold

I have been enjoying reading the electronic copies of Railway "block" signalling : the principles of train signalling and apparatus for ensuring safety by Pigg, James Published [1899?] and The first principles of railway signalling including an account of the legislation in the United Kingdom affecting the working of railways and the provision of signalling and safety appliances, by C B Byles, 1910.

 

To be honest running shunts as such do not crack a mention Not that you would expect them to really). Pigg is adamant that shunting signals are 'stop' signals even if not "stop signals" like home signals etc. Byles makes the more modern distinction in line with the mid 30s rules. (per Rule 16). He distinguishes shunting signals from "running signals", which he describes them as being similar to.

 

Both are clear (forgive the pun) that for a stop signal to be lowered the line must be 'clear' or 'free from obstruction', and the way must be set.

 

Byles notes that for a distant signal to be off the home signal and all other "running signals" be off too throughout the block.

 

Regards

Byles is an excellent book - well worth a read in my view although perhaps a little dated by modern standards.  But read his words on the Distant Signal more carefully - as there are no stop signals within a block [section] it is not possible for them to be 'off' (or 'on').   What he in fact says is accurate - that all stop signals to which that Distant Signal applies (at the 'box in advance) are 'off' and that the line is clear into the next block section, or intermediate block section, (and in effect through that section) - although he expresses it in slightly different words.

 

 The interesting part - compared with more recent definitions - is his explanation that the next section in advance is clear although that might equally be the case if the Distant Signal is at caution or is Fixed At Caution.  Thus it is perhaps more sensible to stick to modern explanation regarding the stop signals to which a Distant Signal applies being 'off'.  But as much as anything that is a function of the way in which language and the wording of the Rule Book has changed and don't forget that Byles was writing more from an engineering rather than an operating background.

 

In explanatory terms it has always been much simpler to distinguish subsidiary signals from shunting signals as they generally serve differeent functions and are found in different places - the only awkward bit is when a shunting signal is mounted as a subsidiary ;)

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Splitting yellow discs,

21 and 22, those and 32 are normal use of yellow discs,

a facing yellow disc on the main

17 which needs to be passed when on if not entering the engineers siding

and trailing yellow discs.....

31 and 39 but it seems very unclear why these need to be yellow. Another case where the locking chart would help.

Regards

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  • RMweb Premium

Not shunt signals but there used to be 2 'black' (ie unlit) signals between sandycroft and mold Jn that you could pass under normal operation, you normally have to stop at an unlit signal (if its possible) or its a spad

 

I'll leave you to guess what they are for, beast66606 will know!!

 

Google maps does give a clue - though down my way similar protection is provided in the same scenario by putting ordinary continuously lit signals back to red from a proceed. Mind you the volume of traffic of both modes is somewhat different to the location you re describing ;)

 

On a serious note though is there any particular reason for having these extra 'unlit' special signals rather than integrate the protection into regular running signals

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  • RMweb Gold

The area around those signals has been resignalled now, its TCB whereas it used to be AB (mold jn and snadycroft boxes) and those signals were extra within the block as it were, they are no longer there as i suspect the new signalling can do as you say and revert the previous signals to danger

 

The 'black signals' i believe were activated by a trip wire, there was no distant signal associated with them either, basically if they are red then there is probably a plane on tge track in front of you!!

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  • RMweb Premium

- the only awkward bit is when a shunting signal is mounted as a subsidiary ;)

 

Which, is actually a pretty common situation, particularly today with colour lights where you have a signal guarding entry to a station which has call on abilities plus the option of entry into sidings. However - before anyone complains, it also has relevance to mechanical signalling because, from photos, a similar combination using a mechanical disc signal for both shunt and call on moves seems to be pretty common in the later days of the big 4 / BR. I imagine this was probably due to signalling renewals as I pre grouping era photos / signalled installations tend to  prefer for call on routes to feature modified semaphore arms specifically for that function and separate of shunt moves.

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39a can't apply to running shunts because the running shunts have to be cleared before the preceding running signal can be cleared.

 

I may have missed it, but I don't think it has been mentioned before on this thread that one important purpose of a running shunt was that it confirmed to the driver of an approaching train that the facing point immediately beyond the shunt was still locked. Otherwise, and in the absence of track circuits, once the previous running signal was restored, the signalman would have been able to release the fpl and throw the points. Of course, the bobby wouldn't do this deliberately, but mistakes can be made and railway signalling is all about making it difficult for simple mistakes to cause accidents.

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  • RMweb Premium

The area around those signals has been resignalled now, its TCB whereas it used to be AB (mold jn and snadycroft boxes) and those signals were extra within the block as it were, they are no longer there as i suspect the new signalling can do as you say and revert the previous signals to danger

 

The 'black signals' i believe were activated by a trip wire, there was no distant signal associated with them either, basically if they are red then there is probably a plane on tge track in front of you!!

 

Interesting stuff.

 

Gatwick has always had its tripwire linked in with the main signalling system and the 3rd rail powers supply feed for an extensive area. It does however seem a bit of an anachronism today though given the frequency of take offs / landings, and how shall I put it the extensive technology the places and airport have at their disposal not to mention the parallel A23 road lacking any similar protection.

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21 and 22, those and 32 are normal use of yellow discs,17 which needs to be passed when on if not entering the engineers siding31 and 39 but it seems very unclear why these need to be yellow. Another case where the locking chart would help.

Regards

Dated 2nd December 1946 so is not right for the box diagram but possibly the closest i can find right now....

 

post-4034-0-37855100-1439931327_thumb.jpg

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  • RMweb Gold

31 and 39 but it seems very unclear why these need to be yellow. Another case where the locking chart would help.

Regards

 

31 can be passed if going to 38 which then routes, but it must be off to use points 7

 

39 can be passed if going to 30 but must be off to use points 12

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  • RMweb Gold

Which, is actually a pretty common situation, particularly today with colour lights where you have a signal guarding entry to a station which has call on abilities plus the option of entry into sidings. However - before anyone complains, it also has relevance to mechanical signalling because, from photos, a similar combination using a mechanical disc signal for both shunt and call on moves seems to be pretty common in the later days of the big 4 / BR. I imagine this was probably due to signalling renewals as I pre grouping era photos / signalled installations tend to  prefer for call on routes to feature modified semaphore arms specifically for that function and separate of shunt moves.

Not the same thing really Phil - in the sort of situation you mention they are effectively either co-located shunting signals or using a shunting signal as a splitting signal off the running routes (e.g. an increasingly common arrangement on the WR from the early 1960s onwards) although the colour light version would obviously be a subsidiary - and effectively in terms of a splitting route was where a position light subsidiary took over the role of a miniature yellow, from around c.1962 in  most new work.

 

The subsidiary shunting signals were in my experience miniature semaphores - not used by either the Western or the Southern Regions who normally used proper subsidiary arms as apposed to an arm with the same markings as a running signal arm.  Use of miniature arms in this way was very common on the LMS and latterly LMR and ScR and was also practiced on the ER and this arrangement was partly a consequence of - and frequently wrapped around various changes of the meaning of Draw Ahead arms, a complex story in itself.  Much of this practice seems to have descended directly from Pre-Grouping practice and that required a lot of rationalisation in the 1930s RCH standard Rules which left some ambiguities - partially solved by the use of the term Draw Ahead.

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39a can't apply to running shunts because the running shunts have to be cleared before the preceding running signal can be cleared.

 

I may have missed it, but I don't think it has been mentioned before on this thread that one important purpose of a running shunt was that it confirmed to the driver of an approaching train that the facing point immediately beyond the shunt was still locked. Otherwise, and in the absence of track circuits, once the previous running signal was restored, the signalman would have been able to release the fpl and throw the points. Of course, the bobby wouldn't do this deliberately, but mistakes can be made and railway signalling is all about making it difficult for simple mistakes to cause accidents.

In the absence of track circuits., fouling bars were present

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In the absence of track circuits., fouling bars were present

Not over the entire length of track between the signals and points concerned!

 

Here's a simple example of a running shunt signal, at Arley on the Severn Valley prior to preservation. I understand that this layout dates from the 1930s, prior to which there was a trailing connection into the yard off the Down loop.

 

http://www.signalbox.org/diagrams.php?id=669

 

Although the signalling was completely rebuilt on reopening the Up signalling is much the same today, the differences being that the double disc is now a single disc, the miniature arm on the Up Home is now a colocated ground disc, and there is a track circuit in rear of the Up Home.

 

The distance between the North loop points and the yard points is too long to provide a bar for the whole length. The modern method of working is: lock both FPLs, clear the disc at the toe of the yard points, then either the Up Home or its colocated disc. For the former the yard points must be normal, for the latter they must be reversed. Presumably this would also have applied prior to preservation.

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Byles is an excellent book - well worth a read in my view although perhaps a little dated by modern standards.  But read his words on the Distant Signal more carefully - as there are no stop signals within a block [section] it is not possible for them to be 'off' (or 'on').   What he in fact says is accurate - that all stop signals to which that Distant Signal applies (at the 'box in advance) are 'off' and that the line is clear into the next block section, or intermediate block section, (and in effect through that section) - although he expresses it in slightly different words.

 

 The interesting part - compared with more recent definitions - is his explanation that the next section in advance is clear although that might equally be the case if the Distant Signal is at caution or is Fixed At Caution.  Thus it is perhaps more sensible to stick to modern explanation regarding the stop signals to which a Distant Signal applies being 'off'.  But as much as anything that is a function of the way in which language and the wording of the Rule Book has changed and don't forget that Byles was writing more from an engineering rather than an operating background.

 

In explanatory terms it has always been much simpler to distinguish subsidiary signals from shunting signals as they generally serve differeent functions and are found in different places - the only awkward bit is when a shunting signal is mounted as a subsidiary ;)

Hmmm, maybe my version is different:

 

A distant signal when at danger in-

dicates that the home signal for the box concerned is at danger ;

when at all right it indicates that, not only the home signal but,

any other running signals for the same box, have been lowered also.

In other words the lowering of a distant signal indicates that the

road is clear up to the home signal for the block signal box next

in advance of the box from which the distant signal is worked.

 

Regards

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  • RMweb Gold

Hmmm, maybe my version is different:

 

A distant signal when at danger in-

dicates that the home signal for the box concerned is at danger ;

when at all right it indicates that, not only the home signal but,

any other running signals for the same box, have been lowered also.

In other words the lowering of a distant signal indicates that the

road is clear up to the home signal for the block signal box next

in advance of the box from which the distant signal is worked.

 

Regards

No different - that's what he says.

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Not over the entire length of track between the signals and points concerned!

 

Here's a simple example of a running shunt signal, at Arley on the Severn Valley prior to preservation. I understand that this layout dates from the 1930s, prior to which there was a trailing connection into the yard off the Down loop.

 

http://www.signalbox.org/diagrams.php?id=669

 

Although the signalling was completely rebuilt on reopening the Up signalling is much the same today, the differences being that the double disc is now a single disc, the miniature arm on the Up Home is now a colocated ground disc, and there is a track circuit in rear of the Up Home.

 

The distance between the North loop points and the yard points is too long to provide a bar for the whole length. The modern method of working is: lock both FPLs, clear the disc at the toe of the yard points, then either the Up Home or its colocated disc. For the former the yard points must be normal, for the latter they must be reversed. Presumably this would also have applied prior to preservation.

 

 

In the absence of track circuits being used to lock FPLs, fouling bars once  longer then the longest wheelbase in use, did ensure that  while FPLs could be released in advance of the train , they at least couldn't be operated whilst the train was Over or just immediate to the locked points in question  . the interlock system would of course ensure also that the lock had to be active before any signals could be cleared of course 

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In the absence of track circuits being used to lock FPLs, fouling bars once longer then the longest wheelbase in use, did ensure that while FPLs could be released in advance of the train , they at least couldn't be operated whilst the train was Over or just immediate to the locked points in question . the interlock system would of course ensure also that the lock had to be active before any signals could be cleared of course

Yes - you can see them marked on the 1960 diagram I linked to, and Arley still uses fouling bars today on all its FPLs (as the only track circuit is in rear of the Up Home, fouling bars are needed to ensure the FPLs aren't moved with a train underneath).

 

However - as you said yourself - they're located immediately at the points themselves. As I tried to explain, the distance between the two points is considerably longer than the length of a fouling bar.

 

It's quite possible - given a short train and a fast signalman - to unlock the FPL on the yard points and change them whilst the train (it would probably have to be a light engine) is between the two points and not fouling either bar. I feel obliged to add, I haven't actually tried! However, to do so, the running shunt disc would have to be thrown back in the crew's face, so they should be alerted. As was said above, the fact the running shunt is off (and has been off since the Home was cleared) proves to the train crew that the route has not been changed since they passed the Home.

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  • RMweb Gold

In the absence of track circuits being used to lock FPLs, fouling bars once  longer then the longest wheelbase in use, did ensure that  while FPLs could be released in advance of the train , they at least couldn't be operated whilst the train was Over or just immediate to the locked points in question  . the interlock system would of course ensure also that the lock had to be active before any signals could be cleared of course 

 

Yes - you can see them marked on the 1960 diagram I linked to, and Arley still uses fouling bars today on all its FPLs (as the only track circuit is in rear of the Up Home, fouling bars are needed to ensure the FPLs aren't moved with a train underneath).

 

However - as you said yourself - they're located immediately at the points themselves. As I tried to explain, the distance between the two points is considerably longer than the length of a fouling bar.

 

It's quite possible - given a short train and a fast signalman - to unlock the FPL on the yard points and change them whilst the train (it would probably have to be a light engine) is between the two points and not fouling either bar. I feel obliged to add, I haven't actually tried! However, to do so, the running shunt disc would have to be thrown back in the crew's face, so they should be alerted. As was said above, the fact the running shunt is off (and has been off since the Home was cleared) proves to the train crew that the route has not been changed since they passed the Home.

These are not Fouling Bars - they are Facing Point Lock Bars although the function is as identified.

 

There is Fouling Bar (or Clearance Bar) shown on the locking sketch for Hitchin South - serves the slightly different purpose of making sure the rear of a train is clear of the point  heel before the points are changed.

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These are not Fouling Bars - they are Facing Point Lock Bars although the function is as identified.

 

There is Fouling Bar (or Clearance Bar) shown on the locking sketch for Hitchin South - serves the slightly different purpose of making sure the rear of a train is clear of the point  heel before the points are changed.

Fouling bars are the generic term , describing a mechanism that the wheel interfered with a long bar to active a certain function , in FPL these are then actually known as locking bars  http://www.irse.org/minorrailways/publicdocuments/PA01%20-%20Mechanically%20Operated%20Points%20v2.pdfpage 11

 

in the case of situations where a clearance distance had to be maintained out of sight of the signalman, sometimes a fouling bar was used, in that case it was known as a clearance bar.

 

in the same vein a vehicle is a generic for a car and a lorry 

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  • RMweb Gold

Ever so slightly off topic....

 

This is one of the subsidiary signals in shrewsbury, it may look like its a normal stand alone shunt disc but its actually the sub for the main signal on the right which is for the centre of the 3 roads! (It's located on the wrong side, my locos signal is on the platform!)

 

2D46F37F-0909-4630-B439-69A84CDF54D7.jpg

 

If you get the sub at that signal you take the left hand diverging road into abbey forgate yard and your next 'signal' is a stop board, ive done it once with the logs when the box couldnt pull the main signal off, if you get the main signal you to round to the next semaphore (that you may be aboe to make out the o the extreme left of the picture) and that has a sub to take you into the other end of the yard!

 

Good old shrewsbury

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  • RMweb Gold

Then there is this one, this time the shunt discs look like they are associated with the bracket signal but they aren't, they are completely different lines

 

21C8A88D-C6A6-4DDA-8DE8-67AE652940D2.jpg

 

The discs are for the siding to the left (coton hill) to take you either towards platform 7 (top) or 4 (bottom)

 

The main bracket signals are for the up line on the right (next to the train i took the picture from) again to take you towards 7 or 4 however between that signal and the platform there is another signal on each diverging route which have miniture arm subsidiary signals to rake you into an occupied platform

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