Signals for Shunting

andrew jukes
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Signals for Shunting

Postby andrew jukes » Wed Oct 27, 2010 9:02 pm

I am trying to get a better understanding of shunt/ground signals.

In the simple situation of a siding making a trailing connection with a uni-directional running line, a ground signal is often used to ‘give permission’ for a train to shunt into the siding. There is some variation in which side of the track to place the signal, but that is not my main concern.

Consider a goods train wishing to pick up or drop wagons in the siding. Assume it would initially stop before the siding and uncouple its brakevan and perhaps part of the train. It would then move forward over the siding turnout and, once clear of the turnout, stop, whistle and wait for the turnout to be reversed and the ground signal to be cleared. It would then enter the siding, couple up (or drop) the appropriate wagons and move forward onto the running line, clear of the turnout. What happens then? How is permission to back onto the rest of the train, couple up and set off given? Does the ground signal get used also for backing along the running line... or is a second ground signal (alongside, or ‘stacked’?) needed?

I have a rather separate question about ground signals on facing points. In this case, a train running along the running line would effectively ignore the ground signal - is that right. And, although I’m mostly thinking about disc ground signals, what happens with position light ground signals on facing points? Having red lights on the running line is confusing.

There are several trailing ground signals planned for my layout at Welwyn. A screen shot of part of the control screen is attached (I hope - it’s an experiment!), from which it can be seen there are three trailing shunt signal positions on the running lines. Basically, I want to figure out how these should be used.

[The circles on the screen are buttons to operate the turnouts - white when available, black when locked; the boxes with numbers are the block/track circuit numbers]

Andrew Jukes
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Welwyn screen shot.tiff

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grovenor-2685
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Re: Signals for Shunting

Postby grovenor-2685 » Wed Oct 27, 2010 11:06 pm

andrew jukes wrote:I am trying to get a better understanding of shunt/ground signals.

Consider a goods train wishing to pick up or drop wagons in the siding. Assume it would initially stop before the siding and uncouple its brakevan and perhaps part of the train. It would then move forward over the siding turnout and, once clear of the turnout, stop, whistle and wait for the turnout to be reversed and the ground signal to be cleared. It would then enter the siding, couple up (or drop) the appropriate wagons and move forward onto the running line, clear of the turnout. What happens then? How is permission to back onto the rest of the train, couple up and set off given? Does the ground signal get used also for backing along the running line... or is a second ground signal (alongside, or ‘stacked’?) needed?

If designing a signalling scheme the signal engineer would discuss the required operations with the operators and then signal for the required moves, paying due regard to any established standards of the company and when he has a choice, any preferences of his own.
In this situation the choice as to whether to use one signal reading to all routes or to have two or more seperate signals would come out of this process, plenty of examples of both to be found.
In general having a shunt signal lead back wrong line was a last resort due to the risk of head ons that it posed. If there was another crossover behind the train then the move back would probably need that crossover reversed. If not then there would be a 'Limit of Shunt' marker. With colour light signalling and track circuits conditions could be applied to only allow the signal to clear for that route if the track circuit was occupied, ie by the brake van etc.
I have a rather separate question about ground signals on facing points. In this case, a train running along the running line would effectively ignore the ground signal - is that right. And, although I’m mostly thinking about disc ground signals, what happens with position light ground signals on facing points? Having red lights on the running line is confusing.

This one needs research into the particular company practice at the relevant time. Alternatives are essentially,
1. The main aspect rules, ignore any in-route shunts,
2. Change the stop aspect of the in-route shunts to something other than red so the train does not have to pass reds.
3. Require the in-route shunts to be pulled off before the main signal can be cleared.
Current practice is option 3. Study of relevant locking tables if available will tell you if 3 was applied to a lever frame but it did create problems with mechanical locking so in-line shunts would ba avoided if possible in mechanical installations.
There are several trailing ground signals planned for my layout at Welwyn. A screen shot of part of the control screen is attached (I hope - it’s an experiment!)

If you had used a .gif file instead of a .tiff the image would have been displayed without us needing to open it in another programme.
from which it can be seen there are three trailing shunt signal positions on the running lines. Basically, I want to figure out how these should be used.

Its not very clear which ones you mean as the directions of the various lines are not identified and most of the potential destinations are out of view?
Regards
Keith


[The circles on the screen are buttons to operate the turnouts - white when available, black when locked; the boxes with numbers are the block/track circuit numbers]

Andrew Jukes[/quote]

andrew jukes
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Re: Signals for Shunting

Postby andrew jukes » Wed Oct 27, 2010 11:43 pm

Thanks, Keith.

Here is a larger picture (as a gif), London to the left and the North to the right. The running signals are notional at this stage, they will all be semaphores, some with co-located distant or shunt signals. The track layout is more or less as at the end of steam - it was a lot more complicated in the late 1930s but space ruled that out. The sidings look hard to shunt and a horse was used until very late on.

The question is if, for example, you want to drop wagons in the down yard, using the crossover from block 504, then it would seem natural to park the rear of the train in block 502, drop the wagons and reconnect to the rear of the train. Would the shunt signal on the down line at the end of the crossover be used both for reversing into the yard and for reversing to reconnect to the train? I think you're saying both moves would be signalled but practice varied, some railways using one disc and some two. I had initially assumed the shunt signal showed the crossover was reversed (and locked) and that the reconnecting move would be unsignalled, but that did seem wrong.

Andrew
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grovenor-2685
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Re: Signals for Shunting

Postby grovenor-2685 » Thu Oct 28, 2010 7:52 am

How long are blocks 502 and 503? the home signals look to far away from the points for mechanical signalling.
Where is the signal box?
Were there any other up/down crossovers, eg in blocks 510 or 511?

Route holding is always an issue with mechanical signalling and it would not be acceptable to release the points in block 504 with block 502 occupied. Hence to do the shunt moves you are suggesting you need another signal at the 502/4 boundary so the existing signal becomes the outer home and could have an LOS just inside it.
The location of the SB is germane to the shunt signal situation as it affects the ease with which the Bobby can communicate with the train crew during these manoevres, more difficult communication needs more explicit aspects, ie more discs, to avoid ambiguity. Generally if the operations are simple and well understood the signal just has to say that the next move can be made. If moves are complex and vary a lot the signals need to give route information so that the shunters know if the wrong route has been set.

On such a busy main line as this I would not excect part of the train to be left on the main with the risk of delaying the next express, it would seem more likely that the whole train would be backed into the yard and shunted from there.
Regards
Keith

andrew jukes
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Joined: Thu Mar 05, 2009 4:15 pm

Re: Signals for Shunting

Postby andrew jukes » Thu Oct 28, 2010 10:58 am

Blocks 502 and 503 are not long enough, of course (502 is 1100mm long). Both will be treated as the overlap of the home signal immediately in rear. On the down side, there is an outer home at the far end of the viaduct and the down distant will be well before that. Does the existence of the outer home make it more acceptable to release the crossovers in 504 even when 502 is occupied?

At the north end of the station, the line enters Welwyn South tunnel and the up distant is north of the tunnel on the prototype (and behind the scenes on my model).

The working timetable for 1938 shows two pick-up goods each way each day working Welwyn North (trains 74 at 05.22 and 317 at 11.18 down and trains 305 at 14.20 and 381 at 00.40 up). Booked times at Welwyn were quite short (11 and 32 mins for the down trains and 7 and 8 mins for the up trains). The notes make it clear that most of these were simple dropping off or picking up of wagons, but I expect the 32 min would have involved properly recessing the train - though unlike today there were quite long quiet periods in terms of express passenger trains.

The signalbox is right alongside block 504, so simplicity in provision of shunt signals seems justified. The earlier track layout included a trailing connection from the down yard to the up line in block 513, but only had a plain diamond in the down line.

Shunting from the down line is also complicated be the proximity of the tunnel. Setting back from 512 using the connection at 510 would best be done with a loco with very few wagons. My assumption was that the rear of the train would be left on 508, a shunt signal co-located with the down starter would give permission to move forward to the tunnel mouth where there would be a limit of shunt board. Shunting of the down yard using a loco is also difficult because the goods shed (roughly where the 506 number is positioned) must not be passed through by locos - hence the horse!

In the up direction, I pictured the pick-up goods stopping on 509, parking the rear of the train, moving forward onto 513 and then dropping or picking up wagons from the up yard. Here, the shunt signal is more remote from the signalbox but I think the signalling could still be kept simple.

I suspect this is a location where some compromises are necessary!

Regards

Andrew

ps Amusing to note that train 381 left Peterborough at 11.00am and took till 5.40am the next morning to reach Ferme Park!


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