Flashing signals

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Flashing signals 18/10/2019 at 20:29 #121161
9pN1SEAp
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In the days before LED and semiconductors, would signals that flashed frequently for divergence (e.g. into platform loops) wear out more than others? Either from filament wear or the flashing capacitors?

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Jamie

Jamie S (JAMS)
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Flashing signals 19/10/2019 at 12:43 #121170
Izzy
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Not really, no.

All the flashing modules (both SSI and relay units) that i have worked with didn't actually flash the lamp. It was pulsed. The difference is that flashing actually starts and stops the supply - it turns on and off. Pulsing just drastically lowers the voltage but never actually turns off, hence the lamp never actually fully cools down - so you get the impression of a flashing lamp, but without the loss of filament life.

This circuitry is built in to SSI signal modules as standard. The "flasher" units that can be found in earlier (than SSI) installations work in the same way as the SSI modules - but with a modified signal head filament changeover relay arrangement to allow the first filment failure cicuits to still operate correctly (which they wouldn't otherwise do with a reduced voltage on the filament when it is dimmed or pulsed).

As for the days before semiconductors.....UK signalling only rarely used flashing aspects that early, and i don't know how they actually were achieved. If you are asking about US practice, then i don't know how their flashing aspects are generated at all, as i have never worked on US equipment, so i wouldn't like to speculate how this is achieved across the pond.

Last edited: 19/10/2019 at 12:47 by Izzy
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Flashing signals 19/10/2019 at 14:17 #121176
9pN1SEAp
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Thanks! My strange curiosity is sated!
Jamie S (JAMS)
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Flashing signals 19/10/2019 at 14:27 #121177
Izzy
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You're very welcome
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Flashing signals 20/10/2019 at 14:54 #121211
Ron_J
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The pedantic mariner in me feels obliged to point out that so called ‘flashing’ signal aspects on UK railway infrastructure should actually be described as occulting in terms of their light characteristic; that is to say the lit phase is longer than the dark phase. If they were true flashing lights then they would be dark for longer than they were illuminated.
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Flashing signals 20/10/2019 at 15:21 #121212
Splodge
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I reckon the Manchester South ones are properly flashing in that case; very strange taking the Stoke line from Edgeley as the flashing double from Edgeley is barely unlit; the single from Manchester south (at Adswood Road Jn) seems barely lit.
There's the right way, the wrong way and the railway.
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Flashing signals 20/10/2019 at 16:15 #121213
Steamer
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From observations, MP641's idea of flashing is to dim to half brightness. It's a Dorman lightweight LED signal; no idea how the drivers interpret it.
"Don't stress/ relax/ let life roll off your backs./ Except for death and paying taxes/ everything in life.../ is only for now." (Avenue Q)
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Flashing signals 20/10/2019 at 16:18 #121214
Ron_J
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Is that Ansaldo kit? They introduced all sorts of oddities.
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Flashing signals 20/10/2019 at 17:14 #121216
Steamer
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Ron_J in post 121214 said:
Is that Ansaldo kit? They introduced all sorts of oddities.
The one Splodge refered to at Addswood Road is.

"Don't stress/ relax/ let life roll off your backs./ Except for death and paying taxes/ everything in life.../ is only for now." (Avenue Q)
Last edited: 20/10/2019 at 17:15 by Steamer
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Flashing signals 20/10/2019 at 19:47 #121217
Splodge
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Steamer in post 121213 said:
From observations, MP641's idea of flashing is to dim to half brightness. It's a Dorman lightweight LED signal; no idea how the drivers interpret it.
As a wrong route :D

Quite surprising, the signals on the Down Styal line approaching the airport have recently been changed to LED heads (seems to be a slow rolling programme of it around Piccadilly, Oxford Road has seen new heads as well) and are now much more distinctly flashing than the old filament ones which tended to dim as you describe rather than 'occulting'

There's the right way, the wrong way and the railway.
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Flashing signals 20/10/2019 at 19:47 #121218
GeoffM
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Some places only start the flashing (etc) part once a train is approaching.
SimSig Boss
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Flashing signals 21/10/2019 at 03:20 #121222
VInce
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Whist on this subject can anyone remember when flashing aspects were introduced into the UK network?

I have a feeling it was in the 80s/early 90s while I was at Derby PSB and Trent PSB. Neither box had any, but I seem to remember that Sheffield and Saltley did.

My failing memory also tells me there were introduced, as is often the case with such things as this, as a result of an incident on the network. Can anyone shed any light on this too?

Vince

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Flashing signals 21/10/2019 at 07:15 #121223
clive
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VInce in post 121222 said:
Whist on this subject can anyone remember when flashing aspects were introduced into the UK network?
[…]
My failing memory also tells me there were introduced, as is often the case with such things as this, as a result of an incident on the network. Can anyone shed any light on this too?
I first saw them at Welwyn North in 1980.

On the Down at Woolmer Green, where the 2-track section ends, you have a 70 mph turnout on a (I think) 115 mph (at the time) line. Approach control from red is clearly ridiculous. Approach control from yellow was used: drivers would see the double yellow at K625 and brake expecting to stop at K635. When they saw K627 with the feather lit, it was easy to control their speed for the turnout.

However, the new (at the time) HSTs had better braking than other trains. An HST doing 100 mph in this situation could delay braking until out of Welwyn North Tunnel and still stop at K635. But if they then came round the corner to be presented with the feather, it at the very least required some harsh braking to get down to 70 mph for the turnout. Even if it was possible, this was undesirable, and so it was therefore deemed necessary to provide extra warning. Adding flashing aspects was cheap because you didn't need new heads on the signal, just a box in the location cabinet to make it flash. (K627 is between two tunnels, so the sighting for a splitting distant is, to say the least, dubious.)

I'm not saying this was the first location so-fitted, but that was the reasoning.

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Flashing signals 21/10/2019 at 17:59 #121236
GeoffM
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VInce in post 121222 said:
Whist on this subject can anyone remember when flashing aspects were introduced into the UK network?

I have a feeling it was in the 80s/early 90s while I was at Derby PSB and Trent PSB. Neither box had any, but I seem to remember that Sheffield and Saltley did.

My failing memory also tells me there were introduced, as is often the case with such things as this, as a result of an incident on the network. Can anyone shed any light on this too?

Vince
According to this page (thanks to Simon Lowe) they were first used at Didcot East Junction in 1979 (Reading PSB).

SimSig Boss
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Flashing signals 21/10/2019 at 20:48 #121239
jc92
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Vince I suspect (pure supposition) that Sheffield got flashing aspects at Dore when it was resignalled from double to single lead circa 1981ish, Swinton on commissioning in 1992 and Aldwarke probably around the same time when the junction was remodelled to be be higher speed from the old layout down from 4 tracks to 2.
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Flashing signals 22/10/2019 at 08:14 #121254
VInce
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jc92 in post 121239 said:
Vince I suspect (pure supposition) that Sheffield got flashing aspects at Dore when it was resignalled from double to single lead circa 1981ish, Swinton on commissioning in 1992 and Aldwarke probably around the same time when the junction was remodelled to be be higher speed from the old layout down from 4 tracks to 2.
I'm sure you are right about Aldwarke. A few of us from Derby had a day "on the district" and although Sheffield was a bit off our patch we purposely rode over the section between Swinton and Mill Race in a First Gen DMU in the hope we would get a good view out of the front - which we did.

The subject of flashing aspects was a regular topic of conversation in the box after that.

Thanks everyone for refreshing my memory

Vince

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