How do repeater signals work

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jim s-w
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How do repeater signals work

Postby jim s-w » Wed Jan 13, 2016 4:42 pm

Hi all

I have a repeater signal on my little layout. One would be one side of a bridge (which you can't see and the other closer to the junction so you can. Both are disused but I want to include the operating gear for them to give a idea that they were once.

So the question is, would both signals be operated from one lever via a single cable or would they be arranged some other way?

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Jim
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grovenor-2685
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Re: How do repeater signals work

Postby grovenor-2685 » Wed Jan 13, 2016 6:08 pm

Repeater signals were normally banner signals and were mostly electrically operated so would need a small battery/relay box.
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Re: How do repeater signals work

Postby dal-t » Wed Jan 13, 2016 6:28 pm

But isn't the real question how would the battery/relay box be activated? I've always assumed the clue was in the name, and a 'repeater' was somehow driven from the main signal, so it could never give a clear indication when the real signal was at danger - but is that true? I also need to build one, idc, although I doubt I'll be able to represent the control gear very accurately (simply don't have Jim's modelling skills!).
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Re: How do repeater signals work

Postby grovenor-2685 » Wed Jan 13, 2016 7:06 pm

"Circuit controllers" were used to link mechanical operations to electrical ones.
The most common designs had a rotary commutator or cam driving electrical contacts, these would look like a little round box 8 - 10 inches diameter with a crank on one side linked to signal arm or weight lever.
Mostly these were used to provide the signal to arm repeaters on the blockshelf but would equally provide a signal to a banner repeater.
On the signal box levers similar circuit controllers could be used or an alternative linear type that could be linked to the tappets, these being in the box would not be visible.
A banner circuit may include contacts on both lever and signal arm or just the latter depending on the policy of the design office.
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Re: How do repeater signals work

Postby JFS » Wed Jan 13, 2016 10:24 pm

Hello Jim,

Are you saying that the driver would encounter two repeaters one after the other for the same arm? Keith might know differently, but I think that would be very unusual - especially with a very low line speed. The driver is expecting the signal to be "on" - the idea of the repeater is to give him advanced warning that it is off so he can keep his train on the move. I have never seen or heard reference to a mechanically worked one - Sykes invented electrical banners well over a hundred years ago after all.

Just to add to Keith's point -there would "never" be a separate lever for the repeater - I would expect both the arm and the lever working it to be in the operating circuit for the repeater that way any "wrong-side" failure of the arm or its contact would not be duplicated by the repeater, as the lever being "not reverse" in the frame would hold the banner "on"

Hope that helps - even if pretty academic in 4mm - where usually you can only see the back of banners!

This chap seems like a keen type in this regard:-

http://www.rmweb.co.uk/community/index. ... completed/

Cheers,

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jim s-w
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Re: How do repeater signals work

Postby jim s-w » Thu Jan 14, 2016 8:01 am

Thanks chaps

I'm thinking of a single repeater and a proper signal. It's all so that I can add some cosmetic signal wire runs which will be mostly buried in undergrowth anyway!

Cheers

Jim
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Re: How do repeater signals work

Postby grovenor-2685 » Thu Jan 14, 2016 9:02 am

jim s-w wrote:Thanks chaps

I'm thinking of a single repeater and a proper signal. It's all so that I can add some cosmetic signal wire runs which will be mostly buried in undergrowth anyway!

Cheers

Jim

Then its not a repeater you want, its either an outer home or a distant, either of which would have their own wire coming from the box.
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Noel
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Re: How do repeater signals work

Postby Noel » Thu Jan 14, 2016 10:43 am

JFS wrote: The driver is expecting the signal to be "on" - the idea of the repeater is to give him advanced warning that it is off so he can keep his train on the move.


It was also used, possibly more often, to let a driver know that he could continue at full speed in circumstances where lack of visibility would mean he would otherwise have to reduce speed in case the signal was 'on'. The GW at least sometimes used repeaters for distant signals as well as homes.

With just a bridge in the way on a low speed line, I suspect that the signal engineers would simply have put the signal the other side of the bridge, without the complication of a repeater [Sorry Jim!].

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Re: How do repeater signals work

Postby JFS » Thu Jan 14, 2016 11:03 am

Noel wrote:It was also used, possibly more often, to let a driver know that he could continue at full speed in circumstances where lack of visibility would mean he would otherwise have to reduce speed in case the signal was 'on'.


A driver encountering a repeater "on" having passed a Distant at "clear" ?????

Now that would be a Brown Trouser moment!

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Re: How do repeater signals work

Postby JFS » Thu Jan 14, 2016 11:12 am

Jim,

I have to confess that when I first saw the pic of signal just inside the bridge, I was thinking along the lines of "Why did they site it there?" One possible way round it might be to provide a tall post with a lower "repeating" arm. They were not exactly common in this circumstance, but it would provide the means to show your admiring public exactly how it would have "worked" operationally.

And if you want wires through the undergrowth, then why not - who knows what lies beyond the bridge?

Cheers,

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Re: How do repeater signals work

Postby Noel » Thu Jan 14, 2016 11:49 am

JFS wrote:A driver encountering a repeater "on" having passed a Distant at "clear" ?????Now that would be a Brown Trouser moment!


No doubt, but drivers were/are expected to be aware of the possibilities of a signal failure, or some sudden emergency, resulting in an unexpected signal aspect. The repeater provides a warning of a problem, or that the signal is clear, where the next signal is not visible at normal sighting distance.

Noel
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Re: How do repeater signals work

Postby philip-griffiths » Thu Jan 14, 2016 1:07 pm

Jim

As you model former LNWR lines in the 'big model'.... I have a book of LNWR signalling in the house. It contains examples where a bridge would have obscured the signal, so the pole was made higher so that it could be seen from the other side of the bridge. if it had to be very high then there were two arms, one set lower down.

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Re: How do repeater signals work

Postby jim s-w » Thu Jan 14, 2016 2:09 pm

I don't know. I just gave the plan to a professional signaller and he said that I needed one (I am sure I've had this conversation already!)

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Jim
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Re: How do repeater signals work

Postby Brian Eves » Wed Jan 20, 2016 5:09 pm

Repeater signals were and still are provided where the driver cannot get full sighting of the signal. In semaphore days, there would be a circuit controller fixed to the signal post and operated from a linkage to the signal arm. This would feed a supply, usually 12V DC to an electromechanical banner. When the signal is in the ON position the banner arm is horizontal position and when OFF the banner is at 45 degrees.

Colour light signals still suffer the affects of not having the required sighting distance. The sighting does change over time. Things like Overhead Line masts and equipment, station lighting and new structures cause the distance to be diminished.
Current standards require four seconds of continuous sighting and 7 seconds of interrupted sighting. At 20 MPH it is not too difficult to achieve but consider that trains travel at 125 MPH.

The semaphore signal described where the main arm is obscured by a bridge or other structure and has another arm upon the same post but much higher is called a Co-Acting Signal. They are worked mechanically from the same lever. A wire or rod connects the two arms together. The height of top arm could be in the region of sixty foot.

As for the comment about a wire run being lost in the undergrowth. A lineman would get his knuckles wrapped if that was the case. (Certainly around Liverpool where I was a linman.)

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jim s-w
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Re: How do repeater signals work

Postby jim s-w » Wed Jan 20, 2016 8:02 pm

Brian Eves wrote:As for the comment about a wire run being lost in the undergrowth. A lineman would get his knuckles wrapped if that was the case. (Certainly around Liverpool where I was a linman.)


Very true but the whole lot is abandoned remember. After discussion on here I've decided not to worry about it. Besides there's nothing to say that the sighting the other side would be any better and the curve would have been dead slow anyway so it's probably not needed.

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Jim
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James Wells
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Re: How do repeater signals work

Postby James Wells » Thu Jan 21, 2016 12:21 am

Brian Eves wrote:As for the comment about a wire run being lost in the undergrowth. A lineman would get his knuckles wrapped if that was the case. (Certainly around Liverpool where I was a linman.)


Sadly not the case now - just don't have the staff to keep on top of it. The number of times we have problems as a result of vegetation getting in the wire runs is just silly in spring and summer.

You can see the wires disappearing into the grass!

ImageMorning Tilcon by James Wells, on Flickr

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Re: How do repeater signals work

Postby Terry Bendall » Sat Jan 23, 2016 8:01 am

Brian Eves wrote:Things like Overhead Line masts and equipment, station lighting and new structures cause the distance to be diminished.


A friend who works on the big railway (and works for ASLEF) was talking recently about a signal on the west cost main line on a curve where the sighting has been restricted by an OHL mast so it does happen still.

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Re: How do repeater signals work

Postby James Wells » Tue Jan 26, 2016 12:19 am

Terry Bendall wrote:A friend who works on the big railway (and works for ASLEF) was talking recently about a signal on the west cost main line on a curve where the sighting has been restricted by an OHL mast so it does happen still.


This is why the signalling system and rules are arranged to avoid a a driver coming up against an unexpected red signal - on AB a semaphore home will only be cleared if the next signal (either Inner Home or Starting as appropriate) cannot be cleared once the train is at, or nearly at, a stand. And in colour light areas, a red will always be proceeded by a cautionary aspect.

There are exceptions - Knaresborough turn rounds are an interesting one. To speed the process up, the inbound working will have the home cleared when Knaresbrough gets the train online, even though the next signal will be on.

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Re: How do repeater signals work

Postby Noel » Tue Jan 26, 2016 11:05 am

jameswells83 wrote:This is why the signalling system and rules are arranged to avoid a a driver coming up against an unexpected red signal - on AB a semaphore home will only be cleared if the next signal (either Inner Home or Starting as appropriate) cannot be cleared once the train is at, or nearly at, a stand. And in colour light areas, a red will always be proceeded by a cautionary aspect.


True in normal operation, James, but, for example, a signalman in a semaphore area may be faced with an unexpected actual or potential obstruction, and return a home to danger after an approaching train has passed the distant at clear. In MAS areas, track circuit clips applied by the driver of a derailed train on the other line may mean that an approaching driver will suddenly face a red after a succession of greens. Also, signal failures happen, and signal design requires that they fail safe, i.e. to red.

Noel
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Re: How do repeater signals work

Postby James Wells » Tue Jan 26, 2016 11:33 am

Noel wrote:True in normal operation, James, but, for example, a signalman in a semaphore area may be faced with an unexpected actual or potential obstruction, and return a home to danger after an approaching train has passed the distant at clear.


In anything other than normal operation, the theory of the rule book always stands but unexpected things happen! Sometimes the rule book doesn't cover it or the Box Instructions give a completely different method. If an unexpected obstacle occurs at least we have GSM-R now to warn drivers if we have sufficent time.

Some things we can never plan for - one of the best was a train stopping to report "someone's garden shed, or at least most of what used to be someone's garden shed is currently blocking the Up Hull!" :D Though perhaps a MOM asking if we can run trains with a helicopter stood in the cess tops that!

Noel wrote:In MAS areas, track circuit clips applied by the driver of a derailed train on the other line may mean that an approaching driver will suddenly face a red after a succession of greens. Also, signal failures happen, and signal design requires that they fail safe, i.e. to red.


You do, however we do get odd situations where a semaphore on TCB will obviously remain off even if the colour light beyond fails - I had this a while back. Train flew by at line speed to see the colour light ahead return to red in front of him! At fringe boxes this arrangement is quite common.


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