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Signalling for Braeintra - Interlocking


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Thanks again for the replies, it’s been a really interesting discussion. 

 

I always think it’s good to be able to find a real life example of something you want to model, and I think Dunkeld is the example to follow for the down end of Braeintra.  For that reason, I think I will stick with no.11 reading straight into the section (LCR), and no shunt ahead arms on no.4 or no.5. 
I haven’t found a real life example of a shunt ahead arm on tokenless block in Scotland.

 

8 hours ago, The Stationmaster said:

Quite what the Shunting Lever at Dunkeld does is unclear to me but in theat lever frame photo there is obviously an interlocking/acceptance lever of some sort (because of its colour) and it is noticeable on the Dunkeld diagram that that there is a Shunting Lever in one direction and a shunting key in the opposite direction.  Their numbering might suggest that the Shunting Lever is used in order to make a shunt past Signal No.5 and the Shunting Key could possibly be involved with a movement in the opposite direction but it does seem over-complicated and might well be something that was done in Scotland to achieve a similar sort of flexibility to that offered by the old Electric Token etc Regulations or to avoid problems with resetting the block after a shunt had been made?

 

I see what you mean about the diagram referring to a shunt lever and a shunt key, but in the picture of the lever frame below you can see that they both appear exactly the same in reality.  I wonder if the pulling of the two levers has different effects on the interlocking?  Also worthy of note is the white collars that denote a lever released by the block – which includes disc no.12.

 

Dunkeld frame

 

I have a question about how the signals work with the shunt token?  The Forbes Alexander booklet on Scottish Tokenless Block states that as no physical token is provided, a train must never enter the single line without the clearance of the section signal, as that is the driver’s sole authority to proceed, “and its clearance indicates that the line is entirely clear for a running move.  It cannot be used to authorise a shunt”.  He then goes on to mention the shunt token is the solution to this.  What is not clear to me reading it is whether the section signal is cleared for the shunt move once the shunt token is released?  It almost reads like the shunt token is the driver’s authority to pass the section signal at danger for the purpose of a shunt, but I find it hard to believe that is how the arrangement works.  

 

Cheers

 

Rick

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>>> It almost reads like the shunt token is the driver’s authority to pass the section signal at danger for the purpose of a shunt, but I find it hard to believe that is how the arrangement works....

 

That was exactly how it worked, the driver took possession of it as his authority to shunt into the section.

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Ok! Thanks. I'm surprised it involved passing signals at danger, but I suppose that actually makes sense so that there's no confusion between a shunt and a movement through the section.  Do you know if the signalman would have given a yellow flag to start the move, or just given verbal permission to move when ready when handing over the shunt token?  I assume the interlocking would allow the shunt back out of the section (into the station or yard) to be signalled normally?

 

Cheers

 

Rick

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13 minutes ago, RailWest said:

>>> It almost reads like the shunt token is the driver’s authority to pass the section signal at danger for the purpose of a shunt, but I find it hard to believe that is how the arrangement works....

 

That was exactly how it worked, the driver took possession of it as his authority to shunt into the section.

So does pulling Lever No.4 release the 'shunt token' - that on its own makes sense and the diagram calls it the 'Up Shunting Token '.. But what then is the purpose of the 'Down Shunting Key' controlled by Lever No 19 (or is it also a shunting token)?

 

As a past signal engineer colleague of mine would say 'it all sounds a bit Indian' - meaning in signal engineering terms that you have to do several things to achieve something which could readily be controlled by only one thing :scratchhead:  As I mentioned previously I think what we might be looking at is something which was devised to try to recreate the flexibility of the Electric Token Block Regulations where a shunting move could pass the Section Signal  at danger while at the same time dealing with the peculiar (to me) idea that a shunting move could not be signalled by a running signal. (which off course it could not  be if a shunting move was simultaneously taking place at the opposite end of the section).  

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1700111464_BraeintraColour.jpg.45c5a21a138d7d2c95c54f019857040f.jpg1452137213_BraeintraLockingv2.jpg.87fa72a37e823933b88ecff6afb1652a.jpg

 

Now that I’m happy the layout is mainly correct, I’ve had a go at a locking chart, based on what I’ve read and what I think should lock what logically.  I’m not sure what the relationship between no.2 signal and no.13 and 15 points should be?  Should a train be cautioned at 2 before being allowed to move up to 4 if the points are reversed (ie; not set for that train)?  I suppose the same could be said for signal no.3 if no.9 crossover was reversed and the movement was being signalled towards no.5 and the up platform, but with no.15 was reversed.  Or am I overcomplicating it?  Any comments on the interlocking gratefully received.

 

I’m also still not sure whether no.17 should be a full size arm or a miniature one?  Or if the post should have both.  It reads up to no.10 which is a shunt disc, can a main arm read to a shunt disc like that?  The down line is permissive, so I think there would need to be a miniature arm, because the track curcuits would lock the main arm if the line ahead was occupied.

 

The other thing I’m questioning is whether the limit of shunt board is right?  Does it need to be protected by another stop signal (an outer home?), or is it just protected by the block?

 

Cheers

 

Rick 

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  • Rick_Skateboard changed the title to Signalling for Braeintra - Interlocking
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2 hours ago, Rick_Skateboard said:

 Should a train be cautioned at 2 before being allowed to move up to 4 if the points are reversed (ie; not set for that train)? 

Yes - if 4 cannot be cleared, for any reason, then an approaching train should be cautioned at 2 (by not clearing it until the train is at, or almost at, a stand)

 

2 should also lock 17. 

3 should be released by 9.

10 should lock 9.

Not sure what's happening with 12/13? I'd have thought one lever to work both points, locked by 4 and 17, releasing 11 and 16.

 

I think all running signals have to read to another running signal, so 17 would have to be a minature - but then can't be used for passenger movements. You could also have a fixed-at-danger signal at the up end of the down platform - I'm sure I've seen an example of that somewhere. If the down line is permissive, you'd need a minature to allow access when occupied. I'm not sure about Scottish practice, the Southern would have had a single disc reading for all three routes.

 

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Thanks, I can see the sense in those additions.  12 is the FPL for 13 (that probably isn't clear from my drawing), which is worked as a crossover.  So I've already got 4 locks 12 and 17 locks 12, which in turn locks 13 in either position.  I've also got 11 and 16 being released by 13R and 15R.  Is it right that points release signals, but signals lock the FPL, where provided, rather than the points?

 

I'm sure you're right about 17 being a miniature arm, I will change it on the next draft.  I don't think any passenger trains will be terminating, so that's not an issue.

 

Cheers

 

Rick

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If you've not got passenger trains terminating, you don't need an FPL on those points, as you'd not have any facing passenger movements over them. There's certainly no need for one on 13B (i.e. the points closest to 11)

 

If a movement needs an FPL engaged, then both the FPL lever and the point lever would be required in the correct position to release the signals. Some companies also required FPLs to be not engaged for trailing movements, for others it doesn't matter. 

 

So with an FPL on 13A:

 

1 - 2R, 4R - Requires all associated stop signals clear

2 - 9N, 10N, 17N, 19N

3 - 9R, 16N, 17N, 18N, 19N

4 - 13N, (12N|12R), 15R, 17N

5 - 15N, 19N

9 - 

10 - 9N, 2N

11 - 13R, (12N|12R), 15R, 16N

12 - (13N|13R)

13 - 15R

16 - 15R, 13R, 12R, 11N

17 - 15R, 12R, 13N, 4N, 2N

18 - 9N

19 - 15N, 5N, 4N, 2N, 3N

20 - 18R, 19R

 

I'd recommend downloading the SigScribe software from Modratec and having a play - you can write out the locking in a text file and import it, and it'll then show you what works and what doesn't.

 

The reason for the home signals in opposing directions locking each other is that the overlaps for 4 & 5 conflict with those for 16/17/19, so if an arriving down train overshot 4, it could potentially hit an arriving up train. You also need to work out where your clearing point is for the single line - most likely, it's 18 - so before a train could be accepted from the next station in the down direction, the route must be clear to that point and points 15 set normal. I think a train for the yard or loop would be brought to a stand at the home and then 15 changed and the minature arms cleared - others more versed in Scottish practice might correct me though.

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6 hours ago, Nick C said:

If you've not got passenger trains terminating, you don't need an FPL on those points, as you'd not have any facing passenger movements over them. There's certainly no need for one on 13B (i.e. the points closest to 11)

 

If a movement needs an FPL engaged, then both the FPL lever and the point lever would be required in the correct position to release the signals. Some companies also required FPLs to be not engaged for trailing movements, for others it doesn't matter. 

 

So with an FPL on 13A:

 

1 - 2R, 4R - Requires all associated stop signals clear

2 - 9N, 10N, 17N, 19N

3 - 9R, 16N, 17N, 18N, 19N

4 - 13N, (12N|12R), 15R, 17N

5 - 15N, 19N

9 - 

10 - 9N, 2N

11 - 13R, (12N|12R), 15R, 16N

12 - (13N|13R)

13 - 15R

16 - 15R, 13R, 12R, 11N

17 - 15R, 12R, 13N, 4N, 2N

18 - 9N

19 - 15N, 5N, 4N, 2N, 3N

20 - 18R, 19R

 

I'd recommend downloading the SigScribe software from Modratec and having a play - you can write out the locking in a text file and import it, and it'll then show you what works and what doesn't.

 

The reason for the home signals in opposing directions locking each other is that the overlaps for 4 & 5 conflict with those for 16/17/19, so if an arriving down train overshot 4, it could potentially hit an arriving up train. You also need to work out where your clearing point is for the single line - most likely, it's 18 - so before a train could be accepted from the next station in the down direction, the route must be clear to that point and points 15 set normal. I think a train for the yard or loop would be brought to a stand at the home and then 15 changed and the minature arms cleared - others more versed in Scottish practice might correct me though.

 

I'll have a look at the SigScribe software, thanks.  

 

I see what you mean about the single line clearing point, I hadn't fully appreciated how the operating regulations  would effect the interlocking in that way.

 

Cheers

 

Rick

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1 hour ago, Rick_Skateboard said:

 

I'll have a look at the SigScribe software, thanks.  

 

I see what you mean about the single line clearing point, I hadn't fully appreciated how the operating regulations  would effect the interlocking in that way.

 

Cheers

 

Rick

It's something I've learnt a lot about recently volunteering on the real thing, but it also comes in handy for models, as it helps to understand why!

 

Rule of thumb is that the clearing point is 440 yards past the outermost home signal, but usually the next running signal, or track circuit joint. In order to accept a train it must be clear, and all facing points set and locked - if, on the other hand, you had an outer home, those points wouldn't be included and could be either way.

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Would 14 need to lock 11, 4 & 5 to ensure the integrity of the single line section or did the shunt token work indirectly, by preventing operation of the instrument when removed from the frame?  I don't know whether Line Clear Release is correct terminology for ScR tokenless block, but I assume same conditions need to apply to 14 lever?

 

Wouldn't 19 lock 2N and 9N as an equivalent control to the single line rule about not letting trains enter a crossing  loop at the same time?

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Hi Michael,

 

I think Line Clear Release is the correct terminology, it certainly appears on the box diagrams.  According to the book, the shunting key can be released under two condtions; section clear or behind another train.  It is electrically released by the block instrument in both instances, and the block is locked until it is replaced.  Because withdrawing the key locks the block, it would not be possible to get LCR for nos.4/5/11, so they will be electrically locked.  Looking at the interlocking at Dunkeld it appears that the shunt key lever does mechanically lock the starters too, belt and braces!  I agree that 19 should lock 2 and 9 normal.

 

Cheers

 

Rick

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20210117_191211.jpg.66e95858e912fecae671ee53414d7b6d.jpg20210117_191236.jpg.9319740ce853804849917fdd5e64d778.jpg

 

The MSE lever frame kit has arrived, and I've had a look at the bits.  The cast levers are nice, although the handle and pull rod to the latch could probably be improved on.  I'm not 100% convinved by the frame arrangement, and I may try to modify it or build something else.  The issues are discussed on this thread.

 

 

 

I've made a start on the locking drawing, but I think I'm making hard work for myself by doing it on paper!  I need to get on with learning CAD.  

 

20210117_191131.jpg.20cbfe8ab285fb0a3afbe1a17ba79aa4.jpg

 

I've got hold of some small 12v electomagnetic cabinet latches that might be a start for electrical interlocking, they have about 4mm of movement.  I've also bought a small rotary swith that may be the start of a circuit controller.  

 

20210117_203700.jpg.1469c577dec69a97cd71a61a60d4830e.jpg

 

Cheers

 

Rick

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Good luck with the MSE kit!  You need to be aware that it has a fundamental flaw - the radius of the quadrants is much larger that the radius struck by the catches so it can never work properly as supplied.  Just ask anyone who has built onebut be prepared for a lot of vituperative invective in response ...    I discovered that fault about 30 years ago and the design has never been changed.  I am tempted to go into a rage ...

 

As I am sure you will know from your researches that an alternative is the scalefour society's frame which is much better, the MkII version also has a kit for the locking.   But then I would say it is better as I designed it(!) and I have built almost 200 levers worth of frames with the locking kits.  The MkII version is only available from exhibitions or to members though given the current crisis, relaxations might be possible on that.

 

for example this 50-lever frame:-

Wellington Locking.jpg

 

You can see plenty of examples of conditional locks.

 

If you look elsewhere in that thread, you will also find a 70-lever frame and you will also find how we implemented the electrical locking:-

 

image.png

 

 

(edited to correct the link)

 

 

Hope that helps

 

Good luck,

Howard

 

Edited by HAB
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Rick,

 

Worth persevering with CAD, as as with the M5 and M1 drawings I produce with it, with your M2 you quickly built up  a library of standard parts for future drawings and its very easy to move parts around within drawing.

 

best wishes,

 

Robert

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On 13/01/2021 at 19:12, Nick C said:

Rule of thumb is that the clearing point is 440 yards past the outermost home signal...

Hi all,

broadly tend to be lurker on here, but thought in this case it worth adding that the RSSB Rulebook, on the matter of clearing points, currently states 440yds for a Semaphore Distant Signal, and 200yds for a Colour Light Distant Signal - I'm not sure when this came into being but perhaps worth looking into if consideration for these is being taken in the interlocking design.

 

Best,

Joe

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Thanks for the replies guys,

 

Howard, the lever frames on the Leeds City thread are things of beauty!  I'm familiar with Leeds as it is today, so I enjoy watching the model coming together.  I’ll have a read of the link from the scalefour forum, thanks.  I’m planning to modify the MSE kit, perhaps even build something new and just use the cast levers.

 

Cheers

 

Rick

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14 hours ago, Joe61264 said:

Hi all,

broadly tend to be lurker on here, but thought in this case it worth adding that the RSSB Rulebook, on the matter of clearing points, currently states 440yds for a Semaphore Distant Signal, and 200yds for a Colour Light Distant Signal - I'm not sure when this came into being but perhaps worth looking into if consideration for these is being taken in the interlocking design.

 

Best,

Joe

The Absolute Block Clearing Point when a colour light distant signal is used was reduced from 440 to 200 yards in the 1980s.  On Tokenless Block the normal Clearing Point (i.e. the loop exit signal) was not affected by this change.  The only situation on Tokenless Block Lines where the change had any effect was at a junction which was not a crossing place.

 

Thus at Braeintra for train approaching off the single line the Clearing point would be 200 yards because there is a clour light distant and it is not a crossing place for a train in that direction (it will be going forward on a double line).  A train approaching in the opposite direction is approaching a crossing place so the clearing point will be the loop exit signal (although the train is arriving on a double line) and the Home Signal would be interlocked already covered above) and worked in the same manner as a Home Signal at a crossing place.

 

However the Signal Box Special Instructions could, if it was considered safe, have amended the basic Regulation and it would be very useful if they were available for Dunkled (although gradients and possibly other local factors could affect what was in them).  We had a 'box on my patch where we were in a vaguely similar situation with a single line becoming double at that 'box (no station) but there all the signals were colour lights and on the double line section the line approaching the start of the single line was also worked by Tokenless Block but in that case towards a c.l. signal with a full overlap - so not really comparable with the Scottish situation.

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