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Post by d7666 on Oct 6, 2023 14:24:58 GMT
After my first trip to Epping Ongar to the diesel gala a couple of weekends ago, questions about it’s single line signalling before preservation. Questions also put to WNXX. Start from the excellent Harsig site and www.harsig.org/PDF/CentralLineEasternExtensions.pdfshowing the 1946 1957 Central Line extensions. Diagram shows Epping [LW] cabin 1 lever and North Weald [LX] 21 lever as Single Line Permission levers. LX21 as “from Ongar” (to North Weald) ; LW1 not specifically marked but obvious it means from Epping [to North Weald]. General question first. It was my previous understanding of Single Line Permission levers both boxes on double ended single line sections had permission levers and both had to be reversed. That does not seem to be the case here ? So how was the single line locked, and then unlocked, for a train ? Electrically lock / release by track circuit ? or some other detection ? or simply manual sight ? Was this permission lever system inherited from GER / LNER / BR or was it implemented by LT at takeover. If the latter, what was there before – specifically token or tablet or staff or ? Present day E0R operation uses tokens but suggest that is something from preservation days and I doubt could be taken as evidence of anything else. There are a lot of remnants of the LT signalling air main but seemed to me most of what was left is towards the Epping end of the E0R. Did the air main extend all the way to Ongar ? I assume it must have done - or were there no train stops beyond a certain point east of Epping ? |
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Post by tut on Oct 6, 2023 17:21:41 GMT
The following is from the Second Supplement to L.T. Traffic Circular (Railways) No. 30 of 1949 titled Changeover of Signalling, Epping.
This all is from the opening of the LT cabin at Epping and closure of the mechanical signal box.
Changes were made in 1957 with electrification of the Ongar branch. If you can get your hands on Supplement to Traffic Circular Railways No. 42 of 1957 all your questions are answered there. Only the most relevant quotations are given below along with a short summary.
The single line was controlled by Epping.
To signal a train from Epping to North Weald, Epping had to get the train accepted, I believe by block bell, by North Weald. North Weald would reverse lever 2 (working the mechanically-operated semaphore eastbound home signal) which could not be replaced until the train was in the platform. I don't think the starting signals onto the single line at Epping would lower until LX2 at North Weald was pulled off. It was not possible to accept a second train until the first had cleared the eastbound platform.
To signal a train from North Weald to Epping, North Weald had to get the train accepted by Epping. Epping would reverse lever 1 which could not be replaced until the train had reached Epping station.
The single line from North Weald to Ongar was controlled by North Weald and was similar. To signal a train from North Weald to Ongar, North Weald had to get the train accepted and reverse lever 3 which worked the colour light eastbound starting signal. Ongar would then reverse their lever 3 which worked the mechanically-operated semaphore outer home signal and then also one of the levers working the mechanically-operated semaphore inner homes (4, 8 or 9). Only then would the starting signal at North Weald, LX3, lower (subject to the track circuits being clear of course). Levers 3 and 4/8/9 at Ongar could not be restored until the train had arrived.
For Ongar to North Weald Ongar would get the train accepted by North Weald and North Weald would reverse lever 21 giving permission for Ongar to send a train to North Weald. It appears the starting signal levers at Ongar were locked until 21 was reversed at North Weald. The colour lights LZ29 and LZ30 would not lower without the track circuits being clear. 21 at North Weald could not be replaced until the train arrived.
But North Weald could close and King Lever 11 could be reversed. In this case everything is the same really between Epping and Ongar just make the necessary substitutions, e.g. to signal a train from Epping to Ongar Epping would need acceptance from Ongar and levers 3 and 4/8/9 reversed. The line was controlled by Epping in this case and they had the permission lever (No. 1).
When Ongar Cabin closed in 1969 LZ30, the station starting signal, became LX21 (21 of course being the old permission lever). Presumably it was all just track circuit controlled with the interlocking being made between the levers at North Weald but I haven't any notices to add detail. Even then it was still possible for North Weald to switch out and King Lever 11 was still in place. If it was switched out No. 1 permission lever at Epping controlled LX21 (formerly LZ30).
When North Weald closed in 1978 what really happened was it became permanently switched out with the king lever 11 reverse.
I can't remember where I found the details I do have on the arrangements following the closures of Ongar and then North Weald unfortunately, I don't have a yellow peril that applies, but it can't have been too hard to find if I found it!
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Post by tut on Oct 6, 2023 17:41:50 GMT
General question first. It was my previous understanding of Single Line Permission levers both boxes on double ended single line sections had permission levers and both had to be reversed. I can't speak for all railways in all time periods, there have been a great many variations and alternative ways of doing things over the years, but that's not something I'm familiar with. I can talk about GWR practice and they had two ways of doing things. With an acceptance lever reversing the acceptance lever in your signal box electrically releases the signals onto the single line in the other signal box. Generally you can't replace the acceptance lever if a starting signal at the other box is off. It is obviously not possible for both acceptance levers to be reversed at the same time, your must replace yours before your colleague can pull theirs. Obviously if you do have your acceptance lever reverse to accept a train your starting signals onto the single line will be mechanically locked by it. And it can be made to do other things like lock power points in advance of the home signals from the single line and you can put timers on the acceptance lever so you can't give the acceptance until a train which has been signalled up to the starting signal has been at a stand for a couple of minutes, etc.
With direction levers the locking is precisely on the direction levers and only the direction levers. If I reverse my direction lever yours is locked and vice versa. Reversing the direction lever mechanically unlocks the the starting signals in your own box, rather than electrically unlocking the starting signals in the other box.
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Post by d7666 on Oct 6, 2023 21:36:11 GMT
WOW !  Thanks for the time to find that lot. Think all the answers are there. |
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Post by d7666 on Oct 6, 2023 21:39:20 GMT
General question first. It was my previous understanding of Single Line Permission levers both boxes on double ended single line sections had permission levers and both had to be reversed. I can't speak for all railways in all time periods, there have been a great many variations and alternative ways of doing things over the years, but that's not something I'm familiar with. I can talk about GWR practice and they had two ways of doing things. With an acceptance lever reversing the acceptance lever in your signal box electrically releases the signals onto the single line in the other signal box. Generally you can't replace the acceptance lever if a starting signal at the other box is off. It is obviously not possible for both acceptance levers to be reversed at the same time, your must replace yours before your colleague can pull theirs. Obviously if you do have your acceptance lever reverse to accept a train your starting signals onto the single line will be mechanically locked by it. And it can be made to do other things like lock power points in advance of the home signals from the single line and you can put timers on the acceptance lever so you can't give the acceptance until a train which has been signalled up to the starting signal has been at a stand for a couple of minutes, etc. With direction levers the locking is precisely on the direction levers and only the direction levers. If I reverse my direction lever yours is locked and vice versa. Reversing the direction lever mechanically unlocks the the starting signals in your own box, rather than electrically unlocking the starting signals in the other box.
I see. This was my flawed understanding of levers in this function then. What I had thought I had understood was reversing both levers was the method to lock the route. Thanks again. |
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Post by tut on Oct 6, 2023 22:11:36 GMT
I can't speak for all railways in all time periods, there have been a great many variations and alternative ways of doing things over the years, but that's not something I'm familiar with. I can talk about GWR practice and they had two ways of doing things. With an acceptance lever reversing the acceptance lever in your signal box electrically releases the signals onto the single line in the other signal box. Generally you can't replace the acceptance lever if a starting signal at the other box is off. It is obviously not possible for both acceptance levers to be reversed at the same time, your must replace yours before your colleague can pull theirs. Obviously if you do have your acceptance lever reverse to accept a train your starting signals onto the single line will be mechanically locked by it. And it can be made to do other things like lock power points in advance of the home signals from the single line and you can put timers on the acceptance lever so you can't give the acceptance until a train which has been signalled up to the starting signal has been at a stand for a couple of minutes, etc. With direction levers the locking is precisely on the direction levers and only the direction levers. If I reverse my direction lever yours is locked and vice versa. Reversing the direction lever mechanically unlocks the the starting signals in your own box, rather than electrically unlocking the starting signals in the other box.
I see. This was my flawed understanding of levers in this function then. What I had thought I had understood was reversing both levers was the method to lock the route. Thanks again.
I'm sure you can see that it makes a lot of sense for the levers in the opposite signal boxes to work in opposition rather than in concert because one box is sending a train to and the other is accepting a train from. If both levers had to be reversed what does that mean, does that mean, say, the single line will be used for down direction movements as an arbitrary convention? Okay so what would we do for an up train? Both levers must then be normal. That would make some sense, right, both boxes agree which way the train is going to go and set their direction lever accordingly and if they both agree you're good to go. And I believe that is exactly what is down in the Up and Down Platform line, platform 4 at Shrewsbury station between Severn Bridge Jn and Crew Jn boxes. How could I forget Shrewsbury, with its eclectic mix of GWR and LNWR signalling? But with that mix in mind, in the Down Main, Up Main, Down Platform (3) and Up Platform (7) have acceptance levers. I think that's because the Up and Down Platform line is truly bi-directional and used as such, whereas all the others have a normal direction of travel with the ability to work over them in the wrong direction. It's worth mentioning as well that they are all of them worked by absolute block and the block instrument for the Up and Down Platform line is specially interlocked to enable the line to be used in either direction. The way that it works is, if you send a train in in one direction, say the up direction, as soon as you've done that, it's an up line now until that first train leaves and then it can be either again. If you want to put another train in the platform from the opposite direction you have to signal it as a wrong direction movement, and there's a special bell code to use in that situation, 2-3-3-3. Now how about that?
But Shrewsbury aside single lines between boxes being fully track circuited and worked with levers are not very common so it's hard to say with certainty what's 'normal'. I'm morally certain, if nothing else, that what the GWR called an acceptance lever somebody else would have called a direction lever, or vice versa. But regarding the method of working where the 'interlocking levers' have to both be in the same position, the problem is I can't imagine it would be very easy to arrange your electrical or mechanical interlocking around that. Clearly it's possible, they did it at Shrewsbury, but they did use block instruments there as well.
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Post by d7666 on Oct 6, 2023 23:51:40 GMT
I'm sure you can see that it makes a lot of sense for the levers in the opposite signal boxes to work in opposition rather than in concert because one box is sending a train to and the other is accepting a train from. If both levers had to be reversed what does that mean, does that mean, say, the single line will be used for down direction movements as an arbitrary convention? Err no that wasn't how I thought it worked. It is an entirely academic point now since I was completely wrong anyway. But, since we have gone into my misunderstanding, it was that if the system was each box had a permission lever working in concert, it is not that complex to devise relay circuitry to lock the single line for a train from A to B if box A then box B reversed their levers in that order, but train from B to A needs reverse lever box B first then box A. Or, that equally could work that train A > B needed B then A reversed, and B > A levers A then B. In all cases route remains locked until track circuit or other detection sequences prove train departed A and arrived B (or v.v.). None of that is any more complex than the relay circuitry behind single line electric token block with track circuit detection at entry and exit points. |
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Post by tut on Oct 7, 2023 0:29:13 GMT
I see, now that's something I hadn't thought of and couldn't say whether it's been tried or not really. Possibly it's very common, possibly nobody thought of it, possibly there's a reason it wouldn't work as well that I don't have the knowledge or understanding to be able to identify. I suppose obviously if you did it that way for one thing the locking of the starting signal levers would have to be electrical, which is fine, it's the same with acceptance levers, but you presumably wouldn't be able to apply any mechanical interlocking to the permission levers.
What I can say from hard experience is that it's, oh, it's so common, to go to put your acceptance lever back and the bloody thing's stuck because the other signaller's left their signal lever out, or you go to pull the acceptance and it won't come because they've forgotten to put their acceptance back. Or I've sent train out of section and written it in the book and turned around and seen that the acceptance is still out of the frame. Or I'll accept the train on the bells and clear the signals and I've not pulled the bloody acceptance. Oh it can happen. And I can see a trap with that way of doing things. I also know that if there's a little fault with the circuitry finding that is a horrible job and if you've got loads of signals involved in it, as they would have had at Ongar with all the discs, that's so many circuits that can affect other circuits. And then what happens (I can tell you this from painful experience) is you go to pull the acceptance and it's stuck because the other signaller has left their acceptance out. So they put it back. But now there's a timeout. And you wait. And you try again, but you've not waited long enough and the timeout resets. And then you try again and you reset it and you tie it up in knots and the Paddington ends up an hour late. That was a good shift that was. The point of all this being is I can sort of see why they might not have wanted to rely on the order that different signallers in different boxes operated their levers and would have defaulted to mechanical locking between levers and an action at one end preventing the same action at the other but allowing the opposite action.
It would also presumably be more complicated to allow the run-round moves shunting onto the single line and then back off it that they provided at Epping.
But I'm not trying to pick holes I'm sure all of these problems could be solved if they had gone down that route and maybe somebody did somewhere I don't really know, but it's an interesting one to ponder.
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Post by d7666 on Oct 7, 2023 12:36:04 GMT
I see, now that's something I hadn't thought of and couldn't say whether it's been tried or not really. Possibly I may have picked up something from an overseas railway and confused the matter. British practice digresses from the rest of the world outside the former Empire. I did think it might have been in German practice, such as described in English here : www.joernpachl.de/German_principles.htmin the route locking description, but having skimmed through this again today, it needs a significant brain concentration effort that I don't have right now. And am aware we are risking moderator comment since we are quite along way from Ongar now. |
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Post by rdm on Oct 7, 2023 15:19:21 GMT
Between Bewdley North (BN), Bewdley South (BS) and Kidderminster(KR) on the Severn Valley Railway there are two systems in use: on the Back Road between BN and BS, Direction Lever (DL) and on the true single line between BS and KR, Acceptance Lever (AL). Both lines are fully track cirduited. The principle difference beteen the two systems as that with DL working the signalbox in rear, on receiving Line Clear on the Block Instrument, reverses the DL at that end, which (a) proves the DL at the box in advance is Normal and (b) releases the Section Signal at that end to allow the train to proceed. Whereas with AL working it is the signalbox in advance that reverses the AL to accept the train, thus releasing the Section signal at the rear box. There are no Block Instruments but trains are offered and accepted on the bells, with movement of the respective AL at the accepting box equating to a Line Clear on the Block Indicator. As with DL working the AL cannot be reversed unless the one at the opposite end of the section is Normal. The circuits are proved electrically by means of plungers on the block shelf. The interlocking between the boxes works in the same way as described by Tut above.
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Post by ertowerty1 on Aug 22, 2024 22:19:49 GMT
I know that this may be slightly off-topic, but the Epping Ongar section was forced on LT who had a very small budget to convert and operate this section of railway. There was a design for a substation to be built at Blake Hall which would have allowed unconditional operation of 8-car trains.
This was never built so Epping substation had to supply traction all the way to Ongar which was outside acceptable traction design. I believe either the signalling was interlocked at North Weald to prevent trains departing in different directions simultaneously.
Blake Hall station lighting was supplied from the current rails, as there was no alternative except oil lamps. I believe that the station staff could tell where the trains were by the brightness of the lights.
As you can see from the above, everything was done on the cheap, cheaper solutions would have been letting the steam shuttle continue or shutting the line completely.
I'm guessing that only the train stops would have been supplied from the air-main, points would have remained mechanical?
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Post by ertowerty1 on Aug 23, 2024 8:07:19 GMT
Thinking about my earlier post the line would have had standard stock which had electrically operated control thus more sensitive to track under voltage, the 62 stock had pneumatic contactors and accelerating actuators so not that sensitive to low track volts hence a single 8-car 62 stock was able to operate on this line.Similarsituation to an 8 car formation on the Chesham branch.
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Tom
Administrator
Signalfel?
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Post by Tom on Aug 23, 2024 22:47:21 GMT
I'm guessing that only the train stops would have been supplied from the air-main, points would have remained mechanical? That's my understanding, though it was all gone by the time I joined LU! |
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