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Placing a GWR Backing Signal

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Placing a GWR Backing Signal

Unread postby South Western John » Fri Apr 24, 2015 12:35 am

I also am building a model railway that is in two intermeshing sections - GWR and SR. On the GWR section I am proposing to use a backing signal to access the MPD. However, I am unsure as to the siting of such a signal.

Does a train (or light engine) approach this signal from the rear so that when the backing signal is pulled off, the train (or light engine) retreats from it, reversing away back towards the rear?

OR - does the train reverse past the signal?
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Re: Placing a GWR Backing Signal

Unread postby Mike Hodgson » Fri Apr 24, 2015 8:03 am

The signal does not imply that the train is retreating from the signal. "Backing" merely means that the movement it authorises is in the opposite direction to the normal direction of flow on that running line, and when it is cleared the train will pass it in the same way as it would pass any other semaphore, except the loco would generally be propelling the train.

For example, if there is a siding off the line reached by a point which is trailing to the normal direction of travel, the train will arrive in the right direction passing the point and the signal, which will generally be sited near the toe of the point. To the driver of a train arriving in the right direction, it is clear to him that it does not apply to him not only because of the two holes, but because he sees the back of the arm (painted white) and that arm appears to the right of the post. When the train is ready to be moved back into the siding, he looks back along the train and he then sees the red front face of the arm and back end of his train will be standing facing it. Having this signal elevated on a tall post enables him to see it past the coaches and platform clutter, much easier than looking for a ground shunt signal. So he can see when the point has been set and he can propel into the siding.

I am not sure that a backing signal would have been used merely for loco movements into a shed. A ground signal would have been cheaper and would generally be sufficient as you don't have to look for it from the far end of a train. I expect somebody will be able to cite an example contradicting this though :)
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Re: Placing a GWR Backing Signal

Unread postby South Western John » Fri Apr 24, 2015 11:58 pm

Many thanks, Mike, for your thoughtful understanding. I take on board your thoughts regarding the preferred use of a ground signal for MPD entry.
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Re: Placing a GWR Backing Signal

Unread postby andrewnummelin » Sat Apr 25, 2015 11:21 am

One example of a backing signal being used for entry to a loco shed was at Blaenavon Low Level. National Archives document MT6-741-1 showing alterations to the station 1893/6 clearly labels the various signals.
Blaenavon was at the end of single line branch. The single line became double a bit before the station and the lines combined again after it to form a loop with platforms either side: approaching the station from the branch the left hand line was designated no. 1 and the right hand one no. 2 - the main station building was on the no. 2 line. The single line ran on towards sidings and an industrial connection.
Approaching the station, just after the line became double, was a trailing connection in the no. 1 line that crossed back over the no. 2 line and linked to the engine shed.
After this was a facing crossover, just before the platforms, so that terminating and departing trains normally used the no. 2 line.
At the branch end of the no. 1 line platform was a backing signal labelled "Backing from No. 1 line to Engine Shed".
Interestingly, at the branch end of the no. 2 line platform was the "No. 2 Line starting" signal, and bracketed on the right of this was "No. 2 Line to Engine Shed starting".
So a passenger train terminating at the station would have taken the left line at the first facing point then gone right at the facing crossover and into the no.2 line platform. The loco would have run forward out of the station onto the single line beyond then reversed back onto the no 1 line: the backing signal would clear to allow "wrong line" running to the engine shed, or far enough to allow the loco to go forward again over the facing crossover to the front of the train in the no 2 line platform.
Interestingly these signals remained long after the loco shed (and the trailing connection to it) were removed. The backing signal and the no. 2 line starting signals may be seen in the poor image number 24 on http://www.andrew.nummelin.me.uk/GWR/Bl ... efault.asp . (This page was written before I found the plan in the National Archives.)
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Re: Placing a GWR Backing Signal

Unread postby Chris Rideout » Tue May 26, 2015 8:22 pm

South Western John wrote:I also am building a model railway that is in two intermeshing sections - GWR and SR. On the GWR section I am proposing to use a backing signal to access the MPD. However, I am unsure as to the siting of such a signal.

The replies so far referred to the GWR backing signal with a red arm and 2 holes in it. The SR used a bow tie shaped arm (resembling a wide letter X) and it displayed a violet light or small green light in the off position. As you have a "mixed breed" of layout, there could be variations regarding who operated what signal. Locations such as the S&D, Basingstoke, and Salisbury leap to my eyes, as I can (just about) remember the old signalling in my junior school days. What I can't be sure about was where I saw them. In later years, as an apprentice, I did see a GWR backing signal at Bristol (1969) and I think that was abolished later that year when the Bristol MAS swept the area and killed off several boxes and hundreds of semaphore signals.

At Waterloo, in the semaphore days, there were "shunt on wrong road" signals to enable locomotives to leave the station on a shunt move and return into another platform line. Strangely enough, colour light signals display a letter X if a train is routed or shunted "wrong line" e.g, "XS" will be displayed on the route indicator if the train is to travel up the Down Slow line. That is obviously a wrong direction move. History seems to be repeating itself.
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Re: Placing a GWR Backing Signal

Unread postby South Western John » Tue Jun 30, 2015 12:14 pm

May I thank both Andrew Nummelin and Chris Rideout for their replies. It would seem that two shunt disc signals are called for, sited at the base of the bay platform starter. The left hand disc would be for a station pilot engine to remove the coaches to a point clearing the MPD entry. The right hand disc would then release the train engine to MPD. As this would be the GWR side of the station, the Southern style "bow-tie" would not be applicable.
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