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GWR Signalling for Terminus


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  • RMweb Gold
12 minutes ago, 5BarVT said:

 

 

Technically a 3’ arm isn’t ‘restricted clearance’, it just happens to be shorter so can fit closer#.  Etch 3 on the MSE kit SOO15/1 is a 3’ steel arm which would be used for signals into sidings and goods loops.  However centre pivot arms (which are restricted clearance) as far as I know are (still) wooden.  MSE kit SOO14 has centre pivot arms on the right hand side, the 3’ arm is top right corner.

For an idea of what one looks like see Droitwich Spa.  They are 4’ arms but the 3’ version is just shorter at each end.

 

Hope this helps,

Paul.

 

As I mentioned previously regarding the signal at Bugle shown in my photo illustrated the obsolescent (by the 1920s) way of using a centre pivot arm to read to a siding (or even a loop in some cases).  I took the Bugle photo in the 1960s so clearly some of these signal could survive for a very long time and one was actually installed at Slough in the mid 1950s because there was no way of erecting a bracket signal in a very constrained site and it survived until the arrival of MAS in 1963 (I have a photo of that one as well).

 

And yes - GWR/WR centre pivot arms were always manufactured using timber.  I don't know when the last completely new ones were erected but they were definitely being erected well into the 1950s on new signal structures which used tubular steel posts (of various diameters on bracket structures in that instance depending on the size and height required for the bracket).  My photo below shows the back of Twyford West's Down Relief Home Signal which was erected, in the 1950s, in the wide six foot which was (and still is)  a relic of broad gauge days - in this case a smaller diameter tube is used for the upright.

 

1517016473_PRESSEDSTEELUNITATTWYFORD1959.jpg.fc5090a578bfc33b1118822917430d58.jpg

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3ft arms of the type needed are indeed on S0014, Colin Waite signal arm etches have been unobtainable for many years unfortunately, the only other source would be on one of the Scalelink etches SLF093  https://www.scalelinkfretcetera.co.uk/product-category/frets/176-oo-gauge/page/2/.

 

You will of course end up with lots of arms not needed. I suggest that once you have decided, email me I may be able to help.

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Hi

Thanks for the help from everyone.

I have some further questions:

On 23/10/2021 at 17:46, Stephen Freeman said:

2) A single post with the main starter and 2 very small brackets, one either side with small arms (centre balance type)

 

On 27/10/2021 at 18:24, The Stationmaster said:

 To suit the period you are modelling - and to mitigate the 'forest of signals' effect  - the ideal signal format to use in both cases is like the signal at Bugle

I understood that the centre-pivot type signal arm was basically used for sighting or clearance reasons e.g. the Bugle signal seems to right next to the railway property boundary. Would the of a use non-centre pivot 3' goods line entry arm (as shown in the book by David Smith) mean that a full sized bracket would be required and that this may tend to overwhelm the layout hence the suggestion for the centre-pivot type.

 

On 23/10/2021 at 17:46, Stephen Freeman said:

It just depends, I think on whether or not the mineral lines would have rated option 1. Or, a cash register signal might have been used

b)What is meant by cash register signal?

 

c) Mention is made of putting signals at the toes of points. Does this literally mean at the toe of the point?

 

d) I had decided that the two mineral lines would be worked the one engine in steam principal. Does this change anything. The lines are railway owned and not private.

 

e) Does the outer advanced signal need to be in advance of home signal or can it be in the rear as shown? Would the normal co-operation between signalman avoid the possibility of collisions?

 

f) Is it a rule that all signals operated by a signal box must be visible to signalman i.e before any electrical detection systems? I may have to change the topography of my layout a bit.

 

Regards

Graham

 

 

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On 27/10/2021 at 18:33, The Stationmaster said:

there is the immediate problem of a locking bar for the facing point leading to mineral line 2 - so the signal needs to be at the toe of that point.  

I have thought of a potential problem. If the splitting needs to be at the toe of point or even a few feet in the rear, to Mineral line 2 the signals would need to be where the signal box is located. Even if it was back in rear of signal box would this be a sighting problem for signalman? Would this be a case where the signals could on the RHS of the line? I would probably have to ensure there would be enough clearance between mainline and carriage siding.

Regards

Graham

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  • RMweb Gold
3 hours ago, bordercollie said:

b)What is meant by cash register signal?

Quick answer to that one as you have the David Smith book.  It’s a colloquial term used by Reading D.O. people for the (G)WR mechanical route indicator.  See Plates 89 on page 154 of Smith.

Paul.

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  • RMweb Gold
4 hours ago, bordercollie said:

Hi

Thanks for the help from everyone.

I have some further questions:

 

I understood that the centre-pivot type signal arm was basically used for sighting or clearance reasons e.g. the Bugle signal seems to right next to the railway property boundary. Would the of a use non-centre pivot 3' goods line entry arm (as shown in the book by David Smith) mean that a full sized bracket would be required and that this may tend to overwhelm the layout hence the suggestion for the centre-pivot type.

The centre pivot arm was used at one time - as in the Bugle signal - for a route to a siding or goods line.  if you use an ordinary 3ft arm you have no choice but to use a full size bracket structure and these would still have been b comparatively rare in the are/period you are modelling.  I took the pic of the Bugle signal (from a moving train) in the first half of the 1960s so you can see that some of these signals had a long life.  and it avoids using a bracket

4 hours ago, bordercollie said:

 

b)What is meant by cash register signal?

 

c) Mention is made of putting signals at the toes of points. Does this literally mean at the toe of the point?

 

d) I had decided that the two mineral lines would be worked the one engine in steam principal. Does this change anything. The lines are railway owned and not private.

 

e) Does the outer advanced signal need to be in advance of home signal or can it be in the rear as shown? Would the normal co-operation between signalman avoid the possibility of collisions?

 

f) Is it a rule that all signals operated by a signal box must be visible to signalman i.e before any electrical detection systems? I may have to change the topography of my layout a bit.

 

Regards

Graham

 

 

b. 'Cash register' as already described by '5BarVT' - officially called a mechanical stencil route indicator and as seen in my photo of one at Reading in the thread linked below.  Having worked in the past with a number of former Reading Drawing Office staff I never heard any of them use the term but that of course doesn't mean that others did use it

 

c.  Yes, literally OR the length of the facing point locking  bar in rear of the toe unless a track circuit was provided in lieu of the locking bar but you could find some signals at junction where teh signal was further from the points in which case there was probably a locking bar for another facing point involved.

 

d.  The two mineral lines would effectively have been worked as sidings unless they were of sufficient length to be consider them more suitable for working by 'One Engine In Steam' Regulations.

 

e.  This is an interesting area where modern ideas, particularly found on heritage railways, can be rather misleading about the way in which signals used to be placed.   As far as possible, and unless particular circumstances & local operating requirements demanded additional provision,  The Home Signal at a single line crossing station was inevitably placed at the toe of the loop points and an Outer Home Signal was not provided.  The Regulations are in respect of shunting etc movements outside (the protection of) the Home Signal which also means 'into the single line section' (even when there is an Outer Home Signal or any other additional home signal in rear of the one at the loop points.    There is technically no need at all to provide a stop signal (e.g. in your layout situation an Outer Advanced Starting Signal) to act as a limiting point or reminder to go no further into when making a shunt - the movement simply goes as far as is necessary in order to make whatever shunting moves are involved.   But sometimes such a signal would be provided if other operating reasons so dictated and if necessary on the GWR it would have a subsidiary Shunt Ahead arm if there was any regular reason for a shunting movement to proceed beyond that signal due to, perhaps, the position of a ground frame worked  siding connection or the length of trains being shunted.

 

f.  The Signalman must be able to see all the running signals (it being  assumed that all ground discs can be seen but they too would need repeaters if they can't be seen) which he controls and if he can't see them then arm and lamp repeaters must be provided - such repeaters became mandatory in the 1902 amendments to the Board of Trade Requirements (although they had existed previously but were less clearly mandated).

 

 

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  • RMweb Gold
2 hours ago, bordercollie said:

I have thought of a potential problem. If the splitting needs to be at the toe of point or even a few feet in the rear, to Mineral line 2 the signals would need to be where the signal box is located. Even if it was back in rear of signal box would this be a sighting problem for signalman? Would this be a case where the signals could on the RHS of the line? I would probably have to ensure there would be enough clearance between mainline and carriage siding.

Regards

Graham

I would think it most likely that the signal would be put in the best place it could be put hence my putting it next to the signal box on 'the wrong side of the line'. (As was of course also the case with the splitting signal at Bodmin).   The locking bar would probably be longer than the signal box and there was nothing wrng with havina few feet between teh signal and the locking bar although it was only a very short distance ;)  Incidentally the locking bar for the facing point at the end of the platform would be within the point itself  hence the platform Starting Signal could be very close to the point toe - it wasn't unusual for locking bars to be arranged in that way

 

BTW I dd carefully try to avoid the 'forest of signals' approach with the main line Home Signal by turning it into the splitting signal but there might even have been a track circuit there with two facing points involved.   The GWR was well into track circuiting prior to the Great War and was additionally undertaking a major programme of track circuit installation from 1913.

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  • RMweb Gold

I should perhaps have said “recent Reading D.O. term”.  Primarily for Mike as he knows who I mean: I suspect GX coined the term in MHA/LR days, it was from him that I “learnt” it.

Paul.

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  • RMweb Gold
6 hours ago, 5BarVT said:

I should perhaps have said “recent Reading D.O. term”.  Primarily for Mike as he knows who I mean: I suspect GX coined the term in MHA/LR days, it was from him that I “learnt” it.

Paul.

I don't think he dared try it on me - or on the several 'old lags' from the D.O. who were working in MHA/LR when I was working there.:jester:     I wonder if GX learnt it from a certain someone at Reading who was not of Western origin and liked to wind up the Reading 'old guard'. (And oddly I first met GX when he was a trainee working on that particular gentleman's section in Western Tower and I still have a very outline SFD which he produced from my initial sketch (which I'd drawn on a piece of scrap A4 paper)

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Hi

 

I have been considering the information received as follows:.

a) I think that shunting past the crossover points from loop would only involve a maximum of 10 clay wagons plus a tank engine. A rough estimation would be 1.1m. I believe that this would be a regular shunting movement.  My next question relates to the effective limit of shunting at a terminus. I am still not sure what constitutes the limit of shunting at a terminus. How should shunting past advanced starter be signaled? Can shunting take place up to the home signal with the advanced starter signal on and without a shunt ahead signal or would a shunt ahead still be required? I don't think the former would allowed so would the shunt ahead signal be required to advance past the advanced starter? I am wondering if the home signals could be moved further in arrears, about 100 scale yards in advance of the first fouling point. This would result in a clearance of 1.1 m from toe of crossover turnout. This would allow shunting to carried within the home signal. With this scenario I think the the outer advanced signal wouldn’t be needed. Correct?

 

b) I have been thinking of moving the signal box to just beyond the end of carriage siding. This would allow the imagined signalman to get better sighting particularly of the main home signals especially if it placed further out, and also siding signals from Mineral Branch 2. Maybe, the loco release ground signals would not be visible but for simplicity I am going say that they are visible.

 

c) What would be the operational difference be between treating the Mineral lines as sidings or One Engine in Steam? I imagine them to be something like 1 to 2 miles long. A token would be required for OES I think.

 

d) If the loco release ground signal on the platform side showed a red light as was GWR practice how would the driver know if he can proceed when the turnouts are set at normal before 3 bar VT? Would it be accepted that the driver can see that how the crossover points where set and proceed accordingly? I have more of less decided to have a double ground signals for loop to branch signal and for movement further along the loop past the branch junction. The next ground signal would display white or green to allow movement down the siding/headshunt or movement onto mainline respectively

 

e) I now understand that the signal must be place at the end of the locking bar or a very short distance in arrears where FPLs occur.

 

Regards

Graham

 

 

 

 

 

 

 

 

I

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>>>>My next question relates to the effective limit of shunting at a terminus. I am still not sure what constitutes the limit of shunting at a terminus. How should shunting past advanced starter be signaled? 

 

In its simplest form, provided that the signalman 'blocks back' i/a/w the Regulations to the next box, then he could simply authorise the driver (verbal or hand-signal) to pass the section signal at danger and shunt as far as was necessary. The GWR did tend to provide subsidiary SA arms for this purpose where such moves would be common, but the rest of those comments would still apply.

 

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  • RMweb Gold
3 hours ago, bordercollie said:

Hi

 

I have been considering the information received as follows:.

a) I think that shunting past the crossover points from loop would only involve a maximum of 10 clay wagons plus a tank engine. A rough estimation would be 1.1m. I believe that this would be a regular shunting movement.  My next question relates to the effective limit of shunting at a terminus. I am still not sure what constitutes the limit of shunting at a terminus. How should shunting past advanced starter be signaled? Can shunting take place up to the home signal with the advanced starter signal on and without a shunt ahead signal or would a shunt ahead still be required? I don't think the former would allowed so would the shunt ahead signal be required to advance past the advanced starter? I am wondering if the home signals could be moved further in arrears, about 100 scale yards in advance of the first fouling point. This would result in a clearance of 1.1 m from toe of crossover turnout. This would allow shunting to carried within the home signal. With this scenario I think the the outer advanced signal wouldn’t be needed. Correct?

The key thing here is shunting outside, i.e. towards the rear of, the Home Signal and that effectively means the signal where the single line becomes double at a loop etc -so in reality it means shunting into the single line section.   Thus moving the Home Signal back would have no effect because you'd still need a signal at the fouling point and that would be the one you are shunting outside.  The movement being block signalled is a shunt outside the Home Signal and a shunt Ahead subsidiary might possibly be provided on a suitably sited stop signal but in any event the authority  to proceed would normally be a verbal Instruction from the Signalman to the Driver.  The only reason for providing a Shunt ahead subsidiary below an Advanced Starting Signal well into the single line section would simply be to let a Driver know that he may pass that signal as well - he already has the verbal authority to make the shunt into the single line.  Provided there are no restrictions such as gradients or other physical features the shunt may then be made as far as is physically necessary once the procedure to allow the shunt has been carried out.  I know of one place where the shunt would have had to proceed for nearly a mile in order to reach a particular siding but usually it would be less than 100-200 yds - solely del pendent on the length of the raft of vehicles being shunted and where they were being shunted to..

 

You only need a Shunt Ahead subsidiary if the movement is a regular feature of booked working and even then it might not be considered necessary (and very often wasn't although that changed over the years.  in your situation I think you could probably get away without one

3 hours ago, bordercollie said:

 

b) I have been thinking of moving the signal box to just beyond the end of carriage siding. This would allow the imagined signalman to get better sighting particularly of the main home signals especially if it placed further out, and also siding signals from Mineral Branch 2. Maybe, the loco release ground signals would not be visible but for simplicity I am going say that they are visible.

U[p to you but note, again, that moving the Home Signal further out saves nothing - you still need a stop signal protecting the fouling point where the mineral branch joins0.

 

3 hours ago, bordercollie said:

 

c) What would be the operational difference be between treating the Mineral lines as sidings or One Engine in Steam? I imagine them to be something like 1 to 2 miles long. A token would be required for OES I think.

It depends as much as anything else on the length of the line and the nature of movements being made over it.  If it becomes an OES section there would almost inevitably be a Train Staff for the line and then of course it becomes  a running line so any trip over the line would need to have a brakevan on the rear end.

3 hours ago, bordercollie said:

 

d) If the loco release ground signal on the platform side showed a red light as was GWR practice how would the driver know if he can proceed when the turnouts are set at normal before 3 bar VT? Would it be accepted that the driver can see that how the crossover points where set and proceed accordingly? I have more of less decided to have a double ground signals for loop to branch signal and for movement further along the loop past the branch junction. The next ground signal would display white or green to allow movement down the siding/headshunt or movement onto mainline respectively

The ground signal at the release v crossover would only be approached by an engine wishing to run round its train - so numerous GWr trains almost inevitably passed a signal at danger if they had been pucj hed back over the release points (and passed overa facing point which had no FPL and wasn't detected by a fixed signal.  The ground signal at the end of the platform sat alongside a running signal which could be lowered for any movement along the running line.  The guiding principle with a white light ground disc or backing signal was that it must be at a point which when standing normal would take anything passing that signal towards a signal with a red light.

3 hours ago, bordercollie said:

 

e) I now understand that the signal must be place at the end of the locking bar or a very short distance in arrears where FPLs occur.

But don't forget that the locking bar can be within the point itself so the signal can go at the point toe ;)   The Twyford West signal shown in the photo I posted earlier was however at the end of the locking bar

3 hours ago, bordercollie said:

 

Regards

Graham

 

 

 

 

 

 

 

 

I

 

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On 22/11/2021 at 02:12, The Stationmaster said:

he movement being block signalled is a shunt outside the Home Signal and a shunt Ahead subsidiary might possibly be provided on a suitably sited stop signal but in any event the authority  to proceed would normally be a verbal Instruction from the Signalman to the Driver.

 

On 22/11/2021 at 01:15, RailWest said:

In its simplest form, provided that the signalman 'blocks back' i/a/w the Regulations to the next box, then he could simply authorise the driver (verbal or hand-signal) to pass the section signal at danger and shunt as far as was necessary. The GWR did tend to provide subsidiary SA arms for this purpose where such moves would be common, but the rest of those comments would still apply

Hi

I think these comments have solved my misunderstanding. I had not realised that a stop signal could be passed whilst "on" with the signalman's permission. As Bodmin did have a shunt ahead signal I may of may not have one on the advanced starter. It may be that this was due to the distance from signal box at Bodmin. Do you think that the Signal box location on my layout would have reduced the need for a shunt ahead signal?

Regards

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Coming  to this rather late, but with an interest in both Bodmin and mineral branches, it seems the fact that Bodmin was a) at the top of a hill, and b) a place where very few trains terminated has been overlooked.  Most passenger trains ran Bodmin Road (Now Parkway) to Wadebridge, pausing at Bodmin GWR only for the loco to swap ends .   The Wadebridge line led into the platform within the run round loop and all trains from Wadebridge ( as in one of your Mineral Lines ) had to run into the platform road and leave from the platform road. both goods and passenger.  Some long goods were divided and half brought up from the Boscarne jct on the Wasebridge line and left in the sidings while the loco and brake went back for the rest, taking the combined load down to the GW main line at Bodmin Road.   The reversal was sensible as locos could work smokebox uphill on both lines. so the otherwise sensible idea of a triangular junction was never applied.   Also stopping was a non issue, you didn't need 1/4 mile beyond the stop signal as the train would just about stop dead on the gradient so operating under section clear but station blocked "Warning" was no problem, except starting again on the gradient. So a goods could leave Boscarne as soon as the preceding passenger train arrived at Bodmin, normally the passenger would be away towards Bodmin Road before the goods was stopped.   

With mineral lines coming downhill to the station the platform would need to be kept clear before the train was allowed into the section, that could also mean the line blocked for a considerable time, With one engine in steam  the station would be tied up while the engine was on the branch, maybe a couple of hours, even with block signalling a couple  of miles might take half an hour if brakes had to be pinned down and released.   Basically the Bodmin arrangement was a one off. a way of getting a station nearer the town on a hill top,   Its not a great basis for a freelance terminus, very interesting to operate correctly as an accurate mode, a right PITA if trying to operate it as a terminus. 

For mineral lines the Severn and Wye would be good  if someone would make suitable locos, 16XX and 2021 classes

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  • RMweb Gold
7 hours ago, bordercollie said:

 

Hi

I think these comments have solved my misunderstanding. I had not realised that a stop signal could be passed whilst "on" with the signalman's permission. As Bodmin did have a shunt ahead signal I may of may not have one on the advanced starter. It may be that this was due to the distance from signal box at Bodmin. Do you think that the Signal box location on my layout would have reduced the need for a shunt ahead signal?

Regards

You signal boxlocation would reduce the need for a Shunt Ahead subsidiary because any shunt move out onto the single line would start from somewhere fairly close to the signal box.  So even if there area fair number of shunts the subsidiary signal might not have been considered necessary in a real world equivalent of your layout.  And contrary to what we might think the GWR didn't spend good money on signals which it didn't think were essential ;) 

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  • RMweb Gold
5 hours ago, DCB said:

Coming  to this rather late, but with an interest in both Bodmin and mineral branches, it seems the fact that Bodmin was a) at the top of a hill, and b) a place where very few trains terminated has been overlooked.  Most passenger trains ran Bodmin Road (Now Parkway) to Wadebridge, pausing at Bodmin GWR only for the loco to swap ends .   The Wadebridge line led into the platform within the run round loop and all trains from Wadebridge ( as in one of your Mineral Lines ) had to run into the platform road and leave from the platform road. both goods and passenger.  Some long goods were divided and half brought up from the Boscarne jct on the Wasebridge line and left in the sidings while the loco and brake went back for the rest, taking the combined load down to the GW main line at Bodmin Road.   The reversal was sensible as locos could work smokebox uphill on both lines. so the otherwise sensible idea of a triangular junction was never applied.   Also stopping was a non issue, you didn't need 1/4 mile beyond the stop signal as the train would just about stop dead on the gradient so operating under section clear but station blocked "Warning" was no problem, except starting again on the gradient. So a goods could leave Boscarne as soon as the preceding passenger train arrived at Bodmin, normally the passenger would be away towards Bodmin Road before the goods was stopped.   

With mineral lines coming downhill to the station the platform would need to be kept clear before the train was allowed into the section, that could also mean the line blocked for a considerable time, With one engine in steam  the station would be tied up while the engine was on the branch, maybe a couple of hours, even with block signalling a couple  of miles might take half an hour if brakes had to be pinned down and released.   Basically the Bodmin arrangement was a one off. a way of getting a station nearer the town on a hill top,   Its not a great basis for a freelance terminus, very interesting to operate correctly as an accurate mode, a right PITA if trying to operate it as a terminus. 

For mineral lines the Severn and Wye would be good  if someone would make suitable locos, 16XX and 2021 classes

The mineral lines on this layout either come to a trap point or come into a siding so there is no reason at all why a train cannot approach on them while there is a passenger train standing in the platform - thus there is no direct comparison with the situation at Bodmin (irrespective of gradients).

 

And of course in any case on a single line at a terminus, especially on GWR Block Regulations, you did not need a quarter mile Clearing Point in advance of the Home Signal unless it was an additional Home Signal (i.e = an outer Home Signal) provided for acceptance purposes.

 

At Bodmin assistance in the rear was permitted for trains coming up the 1 in 40 from Boscarne Jcn so there would be no problem getting away (depending on the load) if a train was stopped at the Home Signal.  The branch Home Signal at Bodmin was 240 yards from the signal box so, in view of the very steep rising  gradient there might in any case have been a modified Clearing point for the the branch.  without the Signal Box foot notes/Special instri uctions we simply don't know what might or might not have been permitted as an exception from the standard Regulations.

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  • RMweb Gold
2 hours ago, The Stationmaster said:

And contrary to what we might think the GWR didn't spend good money on signals which it didn't think were essential

Unlike the NER I am led to believe.

Paul.

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The Bodmin area saw two "interesting" passenger train crossing movements, at least in its later years, both at locations without crossing loops.

 

Firstly the 4.43pm afternoon school train from Wadebridge to Bodmin General crossed the 4.35pm Bodmin Road to Padstow train at Boscarne Junction. I do know how that was done, the school train took the Bodmin North line and stopped clear of the junction until the other train had passed en route to Wadebridge, it then reversed back out on to the single line and reversed again to continue to Bodmin General.

 

Secondly in the early evening at Bodmin General, the 6.15pm Bodmin Road to Padstow (WR) train (Bodmin General 6.25-6.35) crossed the 6.12pm Wadebridge to Bodmin Road (SR) train (Bodmin General 6.33-6.43) and I am not certain how that was done. The most likely scenario is that the two trains swapped locos with a further swap at Bodmin General occurring later in the evening.

 

The timings are from summer 1963 and probably varied by a few minutes in other years.

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On 01/11/2021 at 01:14, The Stationmaster said:

The double disc at the toe of the loop to mineral line 2 points could just as easily be a single disc if the lever frame had been renewed with 3 bar VT locking,

 

On 06/11/2021 at 18:35, 5BarVT said:

If it was on old style frame, it would be a double disc, both with red light.  If a 3 or 5 bar, it could be a single disc reading both ways but still a red light.

 

On 06/11/2021 at 18:43, The Stationmaster said:

the reason for it was because the interlocking used back then did not allow for 'conditional' releases but when Vertical Tappet locking was introduced in the early 20th century conditional locking became possible and technically there was no need for the white light although many hundreds remained.

Hi

I have been trying to understand the older v 3 bar locking. I now understand how the locking was arranged with 3 bar at loco release i.e. both ground signals where locked when points set normal and released when points reversed. Also when either ground signal pulled off it locked the other. Was this conditional locking or was it a type of locking that was not actually conditional but could be done with 3 bar locking? I accept that due to GWR practice that the signal on platform side showed red but that loco could progress down the platform line when points normal.

With the introduction of 3 bar locking white lights could have been used but technically not required. So the signal at the end of the loop adjacent to loco release could been red when "on" but could be passed. Similarly under the old system a double ground signal would have been necessary for loop to branch signal or movement further down the loop. I can understand this as it was basically a splitting signal. However, I don't see how one signal with red aspect would be OK under 3 bar locking. Was it simply that, under the later locking, passing such a signal when "on" was now allowable due to the safety improvements inherent in the 3 bar system?

Regards

Graham

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I think you have a fundamental mis-understanding here :-)

 

The older types of pre-HT/VT locking (eg Double-twist, stud) did not allow for conditional locking (although some frames had tappet locking added later  to provide this). So you could not have the case that when the lever for (say) a ground-signal was pulled it did one set of locking if the point lever was reversed, but a different set of the point lever was normal. Hence again with an engine release crossover as an example, the shunt discs would be released ONLY if the points were reversed. Hence the use of white lights for shunts which had to be passed when 'on' for one route.

 

Once HT/VT frame arrived with a conditional capability, then you could have the case that the shunt discs could be worked for either route, as the frame allowed for different locking to be applied applied depending upon the position of the points.  As a ground signal could now work for more than one route, then it was preferable - indeed probably essential - that it had a red rather than a white light as it had to be obeyed regardless of the route.

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10 hours ago, RailWest said:

As a ground signal could now work for more than one route, then it was preferable - indeed probably essential - that it had a red rather than a white light as it had to be obeyed regardless of the route.

Hi

Thanks. Yes I did have a fundamental misunderstanding as I had expected. I think I now have it, as follows: With 3 bar Vt a single ground signal when on meant that the driver couldn't proceed. When off the driver could proceed, depending on how the points had been set.i.e. in my cases a) onto branch or down the loop towards headshunt, and b) loop onto mainline over crossover or into headshunt. Was the situation at the loco release crossover a special condition?  As when the points were normal signals was locked?

Regards

Graham

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>>>Was the situation at the loco release crossover a special condition?  As when the points were normal signals was locked?

 

Sadly I can't answer that without sight of the actual locking table. I have come across situations elsewhere (non-GWR) where the the starting signal at the end of the platform could not be pulled off until the shunt signal in rear of it had been cleared first, but I'm not familiar enough with GWR practice in such situations. Hopefully the Stationmaster will be able to help in due course....:-)

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16 hours ago, bordercollie said:

Hi

Thanks. Yes I did have a fundamental misunderstanding as I had expected. I think I now have it, as follows: With 3 bar Vt a single ground signal when on meant that the driver couldn't proceed. When off the driver could proceed, depending on how the points had been set.i.e. in my cases a) onto branch or down the loop towards headshunt, and b) loop onto mainline over crossover or into headshunt. Was the situation at the loco release crossover a special condition?  As when the points were normal signals was locked?

Regards

Graham

It is probably best to ignore release crossovers when it cmes to locking for the simple reason that the associated ground signals weren't necessarily regarded in teh same way as ground signals at other facing point ends.

 

The practice of providing a signal for a release crossover started by using a non-independent signal - i.e. the signal (a rotating lamp with different coloured and shaped 'targets' on its two faces).  Thus this type of signal only gave a proceed indication when the engine release crossover was reversed - in order that the engine could be released by crossing it to the run round loop.  It seems fairly certain, as known locking charts show, that this principle effectively remained once independent ground disc signals began  to be used instead of a non-independent signals.  That was an entirely logical decision because in the vast majority of cases the engine of an arriving train train would be released via the crossover and would not/could not run back along the platform because its train was in the way.  Clearing the signal back along the platform line only made a degree of sense if the incoming engine was shunt released by another engine shifting its train off it thus allowing it to run back along the platform.

 

Add to that that a simple release - without any conditions having to be taken into account - was cheaper and simpler to incorporate in the locking than a conditional release (or even more so if other potentially conflicting signals needed to have conditional locks).    The oddity in GWR practice - as existed at Bodmin (Princetown was another example) - was providing a ground signal for the point end in the run round loop.  Again it was logical not to prob vide such a signal because the loop was a siding and the only movement through the crossover standing reverse would be from the platform line.  I suspect that the ground signal at Bodmin might have been provided because trains were possibly signalled in to terminate in the loop - rather different from normal practice at a terminus on a single line but we would need to see the signal box footnotes, it isn't mentioned in the 1939 Sectional Appendix.

 

There is a locking table for Bodmin on the SRS website and it appears to be a copy of the original Reading D.O. locking table.  We do not know if it was accurately copied or indeed if the locking table was subsequently altered at some time but as drawn the release crossover signal locking was 100% self contained in that the crossover released the two ground discs and they locked each other and one of the discs could give a proceed indication which directly conflicted with signals reading in the opposite direction - but on a siding so it didn't matter because a hunter would be in charge.  Quite why anybody would want to make a movement from the loop to the stop block end of the platform is something I find rather difficult to comprehend except in order to release an engine which had brought a train into the loop to run round via the platform line (and thus pass at danger the disc at that end of the crossover!).

 

Single or double, and multiple. discs on the GWR went though a number of phases and their use was not wholly governed by the capability of the interlocking, and the principle seems to have changed over the years.  Thus during some of the inter-war years double or multiple discs were provided in new work where it was considered that their provision would be beneficial to the working.  But during the 1940s, including post-war no only were single discs the normal way of doing things but even with 5Bar VT frames they didn't necessarily come with conditional locking to allow them to read to all possible routes through what was a normally trailing running line point.  Thus even in the late 1970s there were situations where movements had to be handsignalled because there was no fixed signal for that particular route in a lever frame which had been renewed and relocked as late as 1949.

 

And I was thinking very much in terms of the traffic situation when sketching in that double disc at the connection to Mineral Line 2 on your layout plan.  Yes it could indeed be a single arm disc with conditional release  but as far as a Driver and Shunter were concerned definitely knowing they were heading onto the Mineral Line, instead of over the short distance to the exit disc from that loop, could allow a significant advantage in handling the movement.

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Goods trains from Bodmin Road were booked to arrive at the General while the platform was occupied with a passenger train (which then immediately departed for Bodmin Road). As far as I can see this could only be made to happen by the goods being routed on arrival into the loop.

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