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Pont Llynfi (spelling corrected)

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Pont Llynfi (spelling corrected)

Unread postby tynewydd » Tue Jun 3, 2014 5:07 am

Next up for discussion is Pont Llyni Junction (PLJ) - the junction station between Port Dinllaen (PD) and Caernavon for the Nantlle branch.

The track plan is here

I think it is fairly conventional design - with a couple of exceptions.

1) It has a single facing point in each direction leading to Pl3 and the marshaling and goods yards.
2) Because of the presence of a pair of high-level viaduct/bridges that encapsulate the station, there are some co-acting signals. This viaduct is use of modeling license, carrying the single line from PD to Tan-Y-Graig, but being nowhere near the correct route.
3) Both Pl2 and 3 are both signaled for bi-directional working to allow fast trains to overtake.Pl3 is also down relief while Pl2 plays that role for Up.

The signaling is part of the CLC/GCR Irish Extension as outlined for PD - and was equipped as that box is with pneumatic controls. The actual signaling is LMS.

Special types of working include branch slip coaches dropped by down express trains and added back onto up expresses and the adding of a milk tank to Nantlle trains. This is why there are calling on signals for Platform 2/3.

Anyway, please let me know if any thoughts occur or I have made some errors in judgement.

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Re: Pont Llyni

Unread postby Danny252 » Tue Jun 3, 2014 11:15 am

1) It has a single facing point in each direction leading to Pl3 and the marshaling and goods yards.

Not sure why that's unconventional - it's what I'd expect, to be honest, as it's the minimum amount of facing points required!

3) Both Pl2 and 3 are both signaled for bi-directional working to allow fast trains to overtake.Pl3 is also down relief while Pl2 plays that role for Up.

My instinct is that P2 would only be signalled in the down, with P3 used for any overtaking use in either direction - however, the layout is all controlled by one box, so it's doable.

For the branch homes, I would've expected a calling on arm to allow an engine to set back onto stock in the platform, even if this occurred rarely in actual operations (as per your brief). Depending on how you work the slip coach, it could also be used in shunting that to/from a branch train.

I also think there should be one on the Up Home bracket for P1, to allow the attachment of the return slip coach - I don't think it would be acceptable to shunt it over the crossover via the discs, given that it would be carrying passengers from Nantle (after being detached from a branch train), but I could be wrong. However, perhaps you intend to do it in P2, hence the calling on for that platform?

I'm not too sure of the use of calling on arms at the right hand end of the platforms.

Double yellow discs - can someone confirm that this would be the practise? I've never seen stacked discs when a yellow disc was involved, but it almost certainly happened somewhere (cue new thread discussing examples?).
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Re: Pont Llyni

Unread postby jc92 » Tue Jun 3, 2014 12:10 pm

I've only seen yellow stacked discs once (can't remember the location). if there is more than one route from the headshunt (eg a yard with a headshunt, and then a left hand exit onto a running line, and a right hand exit onto a running line). in this case, if both discs are on, movements can run into the neck/HS. if one or the other is off, it indicates the signalled route (as per normal red band discs).

the other situation i can think of is where the crossover from the exit signal could lead onto more than one running line (eg up line and down line) and indication of this would be preferable.
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Re: Pont Llyni

Unread postby Danny252 » Tue Jun 3, 2014 12:48 pm

To make it clear (which I didn't before!), I was wondering whether it would be yellow/yellow, or top yellow and bottom red. Sounds like it may well have been the former, which makes more sense, else you'd have to argue that the top yellow gives you permission to pass the bottom red at danger.
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Re: Pont Llynfi

Unread postby tynewydd » Tue Jun 3, 2014 2:18 pm

Danny252 wrote:For the branch homes, I would've expected a calling on arm to allow an engine to set back onto stock in the platform, even if this occurred rarely in actual operations (as per your brief). Depending on how you work the slip coach, it could also be used in shunting that to/from a branch train.

I was certainly missing an calling on arm for the Bay Platform on the branch home bracket - so I added one. Is that the only place you meant?

Danny252 wrote:I also think there should be one on the Up Home bracket for P1, to allow the attachment of the return slip coach - I don't think it would be acceptable to shunt it over the crossover via the discs, given that it would be carrying passengers from Nantle (after being detached from a branch train), but I could be wrong. However, perhaps you intend to do it in P2, hence the calling on for that platform?

Well, yes, I did intend that to be a platform 2 operation, but now thinking about it, that is a long way round for an express, isn't it? So I added one to the Up home bracket home for Pl1.

Danny252 wrote:I'm not too sure of the use of calling on arms at the right hand end of the platforms.

Actually I intended those for shunting out onto the Up as it is "wrong direction" working. That's incorrect, I take it? I now realize that I subsequently added the two stacked ground discs that control the exit onto Down and the Up from the road as well, so that's all certainly odd. I have removed both the subsidiaries on the RHS platform starters and those stacked discs and substituted a home (for the Down) with a bracket arm holding a miniature arm (for moves to the Up). As you pointed out, that could include a passenger coach being moved to Platform 1.

For Platform 2 moves shunt moves on the down, the Pl2 starter will have to be cleared. which is OK as there is an advanced starter. The alternative would be no AS, shunt signal + shunt limit and lots of "Shunt Ahead" bells, I think. Right now there will be "Blocking Back Outside Home" for all shunt moves to the Up and "Block Back Inside Home" for goods moves from Down to Up via the trailing crossover into the Brewery, which I could convert into only needing BBIH just for the coach working to Up by adding an outer home on the Up? The same applies to the Branch as well?

Edit: Actually, thinking about it, the shunt moves to the Up for a coach to be added to an express would be done under cover of the TOS not having been sent yet to the previous box (in this case Trefor), so no BBOH in that case.

Danny252 wrote:Double yellow discs - can someone confirm that this would be the practise? I've never seen stacked discs when a yellow disc was involved, but it almost certainly happened somewhere (cue new thread discussing examples?).

Also - what is the alternative you would suggest? In this case the route indications are to the Branch and (via the crossover) to the Up both for departing goods trains or shunting locos to the branch only. Those could have arms on a bracket or just a vertical arrangement of miniature arms, of course, but how would the shunting line be indicated - by a third arm that is nearly always pulled off, perhaps?

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Re: Pont Llyni

Unread postby Danny252 » Tue Jun 3, 2014 3:53 pm

I was certainly missing an calling on arm for the Bay Platform on the branch home bracket - so I added one. Is that the only place you meant?


Yep, that's the one.

Actually I intended those for shunting out onto the Up as it is "wrong direction" working. That's incorrect, I take it?


Yes, as a subsiduary has a specific meaning (calling on, shunt ahead, or warning, none of which are applicable here) - the miniature arm you replaced it with is more suitable. You will also need an LOS on the Up line to indicate where the short arm gives authority to - otherwise, the engine driver could chuff wrong road all the way to Port Dinllaen, as he's not seen any signal or LOS telling him to stop!

Right now there will be "Blocking Back Outside Home" for all shunt moves to the Up and "Block Back Inside Home" for goods moves from Down to Up via the trailing crossover into the Brewery, which I could convert into only needing BBIH just for the coach working to Up by adding an outer home on the Up? The same applies to the Branch as well?

Edit: Actually, thinking about it, the shunt moves to the Up for a coach to be added to an express would be done under cover of the TOS not having been sent yet to the previous box (in this case Trefor), so no BBOH in that case.


Shunting a train into the section before giving TOS for a different train seems a bit iffy. If nothing else, I'd want confirmation from the guard that his train is complete before shunting out onto the Up Main. Otherwise, there's a risk that the slip coach shunt could be hit by a runaway part of the arriving train, following some way behind the first part.

Otherwise, your use of BBO/BBI seems fairly sensible. Depending on the company's regulations, shunts onto the branch may have been performed under token/tablet/staff released for shunting purposes, to protect the shunt move - that would also depend somewhat on the instruments used, as I know some early instruments weren't able to return an authority to the same instrument it was released from.

tynewydd wrote:
Danny252 wrote:Double yellow discs - can someone confirm that this would be the practise? I've never seen stacked discs when a yellow disc was involved, but it almost certainly happened somewhere (cue new thread discussing examples?).

Also - what is the alternative you would suggest? In this case the route indications are to the Branch and (via the crossover) to the Up both for departing goods trains or shunting locos to the branch only. Those could have arms on a bracket or just a vertical arrangement of miniature arms, of course, but how would the shunting line be indicated - by a third arm that is nearly always pulled off, perhaps?


See my later clarifying post - I had meant to ask if it would prototypically be two stacked yellows, or instead a yellow and a red, purely as stacked yellows looked a bit odd. I have no issues with the actual arrangement and intention!
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Re: Pont Llyni

Unread postby John Hinson » Tue Jun 3, 2014 5:38 pm

Danny252 wrote:See my later clarifying post - I had meant to ask if it would prototypically be two stacked yellows, or instead a yellow and a red, purely as stacked yellows looked a bit odd. I have no issues with the actual arrangement and intention!


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Re: Pont Llyni

Unread postby kbarber » Tue Jun 3, 2014 5:59 pm

As the signalling seems to be LP pneumatic as used by both the LSWR and the GCR, and installed over a wide area (thus akin to the LSWR Woking - Basingstoke scheme), I suspect that rather than Absolute Block working and consequent BBI/BBO and shunt ahead signals, there would be long stretches of automatic signalling (home-over-distant or even the new-fangled three-position arms), with PL box having a control on a rear signal sufficiently far out to protect any shunts. So far as shunting ahead is concerned, I don't know what the regulations were on the LSWR main line but I suspect, at this early date, the automatic sections (apart from one or two on the approach and the first in advance) weren't indicated in any box (I would welcome confirmation). That would replicate American practice of the day, from which this system was derived. If there were unindicated auto sections between signalboxes, there would seem to be no need for any bell signals for shunting ahead - the advance box would never need to know what you were doing in a section he had no indication for. (Of course a UK operator might have felt it needed to be done anyway, however superfluous; again further information would be welcome.)

None of this applies to the Nantlle Branch, of course, where standard single line instructions of some flavour would apply. I think it's a bit unlikely that anyone would go so far as to install any kind of tokenless or track circuited system to even a single section up there :-)
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Re: Pont Llyni

Unread postby davidwoodcock » Tue Jun 3, 2014 6:51 pm

Can anyone confirm whether or not the CLC used stacked discs, I would have assumed that they didn't until the joint lines got subsumed into the LMR and then (surely) only where layouts were altered?

The LSWR LP pneumatic signalling areas originally used rather distinctive miniature arm shunt signals (and a yellow version certainly existed from c1925 because there is an HC Casserley photo showing one), but I am not sure what the GC used. Presumably the CLC would have followed the GC.
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Re: Pont Llynfi

Unread postby John Hinson » Wed Jun 4, 2014 6:00 am

davidwoodcock wrote:Can anyone confirm whether or not the CLC used stacked discs, I would have assumed that they didn't until the joint lines got subsumed into the LMR and then (surely) only where layouts were altered?

Probably not - but the first post says that the signalling is LMS and the LMS certainly did.

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Re: Pont Llyni

Unread postby tynewydd » Wed Jun 4, 2014 1:54 pm

kbarber wrote:As the signalling seems to be LP pneumatic as used by both the LSWR and the GCR, and installed over a wide area (thus akin to the LSWR Woking - Basingstoke scheme), I suspect that rather than Absolute Block working and consequent BBI/BBO and shunt ahead signals, there would be long stretches of automatic signalling (home-over-distant or even the new-fangled three-position arms), with PL box having a control on a rear signal sufficiently far out to protect any shunts. So far as shunting ahead is concerned, I don't know what the regulations were on the LSWR main line but I suspect, at this early date, the automatic sections (apart from one or two on the approach and the first in advance) weren't indicated in any box (I would welcome confirmation). That would replicate American practice of the day, from which this system was derived. If there were unindicated auto sections between signalboxes, there would seem to be no need for any bell signals for shunting ahead - the advance box would never need to know what you were doing in a section he had no indication for. (Of course a UK operator might have felt it needed to be done anyway, however superfluous; again further information would be welcome.)


In such a system, how does the box get informed/requested to accept a train with its class/direction early enough to not cause delay to an express but not too early on a goods (and so inhibit local shunting)? Would there be some form of train describer (and how was it set) or were there still block bells from the box in the rear?
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Re: Pont Llyni

Unread postby Mike Hodgson » Wed Jun 4, 2014 3:21 pm

I think a train describer is unlikely in North Wales for the scenario being modelled.

Sometimes a special bell code might be used for a train conveying a slip portion. It was important to identify such trains correctly as if a coach was slipped prematurely, there was a risk that train out of section might be given when the main train passed and the slip guard was sitting in the middle of nowhere wondering how late his shift was going to finish today. There was also a risk that the guard might attempt to slip but the mechanism might fail and the coach would be overcarried.

Special tail lamps might be carried to distinguish the end of the the various slips portions (some trains could convey slips for more than one destination).

Box instructions sometimes specified that trains of certain classes were to be offered on immediately whilst others must wait for TES etc. The journey time for slow goods vs express passenger would be known, so the signalman in advance should know whether he was all right to continue shunting for a few minutes (assuming there were outer homes etc to allow this). He also has his WTT (which in practice he knows) and special train notices so he knows when the crack trains are imminent and when he should be OK to block the station with shunting. The pick up goods will be timetabled to allow this. And there would be telephone/telegraph traffic to keep him advised of late running of important trains.
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Re: Pont Llynfi

Unread postby tynewydd » Wed Jun 4, 2014 7:03 pm

So I now realize from all this discussion that I should probably have included the signaling at Trefor junction as being inside the scope of the Pont Llyni box rather than having it's own box - which would make perfect sense as there are no stops in between. That way the Cricceth box can offer goods trains (maybe even using permissive block if we assume Goods Only) to PLJ. Port Dinllaen would be the down box, and the next box up the line would be Caernavon on the Up. By having an automatic section between PD and Trefor and another between Trefor and PLJ, we can have increase traffic density during those boat arrival and departure rushes.

Would there need to be something special about the Block Instruments for PLJ and PD when with working automatic blocks? After all, one assumes that PLJ could accept a train from PD or Cricceth even if a subsequent section (like the station) was occupied as long as the initial section was clear to its own clearing point. But you would still want the signalman to be aware of the occupancy of the subsequent sections (like the station) to avoid clearing signals too soon. I guess I can see how this would work if the LC and TOS was all about the initial block and then rigorous track circuiting took care of the subsequent section signal interlocks, but what about where there is a junction and so a subsequent (automated) block could be impeded by a merging train from a different direction? Does that imply that the junction has to be at the boundary between boxes? So PD would be offering to PLJ and the acceptance is really at Trefor?

Adam

PS I'll add the Trefor section(s) to the picture later today.
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Re: Pont Llyni

Unread postby Pete2320 » Wed Jun 4, 2014 10:43 pm

I've looked through this discussion and it seems to be resolving itself nicely but I'll comment on one or two points I've picked up on.

Trevor Junction
I think this would have been provided with its own signalbox even if the LP system was in use here as until 192x there was still a limit on the distance that power operated points could be operated from a box. I think this distance would be (well) exceeded because Pont Lyni box is at the opposite end of the station and TJs down distant is not under PLs advance starter (with possible repeat under at least the P2 platform starter) suggesting TJ is more than braking distance from PL. However, there is nothing to stop the box having been abolished subsequently but my gut feeling is that this would not have happened if TJ is as far away as I suspect. I also have a suspicion that the true LP system was not efficient over long distances but of course we can reasonably assume that these boxes were converted to EP operation as were all the GCR and L&SWR boxes.

Automatic Signalling
As suggested, this might well have been a possibility certainly for the longer "block (sic)" sections. Outer homes would be essential, at least in the sense that the last signal before the inner home would need to be controlled. No LC, TOL or LB would be used, trains only being descried. Not sure how this would be done, a bell is probably simplest but it would be reasonable to assume that the same system as used on the L&SWR would be used- whatever that was!

The West End
I don't think that route from P3 to the Limit of Shunt would have been provided unless clearing the Down Main was a priority. I don't see any objection to shunting the loaded Slip Coach onto the back of an Up express via the down main and then the "Brewery" crossover on the authority of disc signals. This may not be permitted by modern signalling principles but we are not talking a modern installation here. As it is the said Slip coach has to get to the LOS on the authority of a miniature arm which has the same meaning as a disc. However if that LOS was provided, given its' use I feel certain that there would have been an outer home. But is this going to conflict with Trevor Junction?

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Re: Pont Llyni

Unread postby StevieG » Wed Jun 4, 2014 11:49 pm

John Hinson wrote:
Danny252 wrote:See my later clarifying post - I had meant to ask if it would prototypically be two stacked yellows, or instead a yellow and a red, purely as stacked yellows looked a bit odd. I have no issues with the actual arrangement and intention!


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Not necessarily appropriate for Pont Llyni, but as stacked yellow discs have been a reality (as have 2-up stacked 'yellow' ground position-light shunts, for that matter), hypothetically, in general terms, it would appear that a single yellow disc with a route indicator, still passable when 'On' to a headshunt or such, could have been a possibility, though hardly an ideal solution.
But has there ever been a real example of this?
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