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"Permissive" shunt signals 20/11/2015 at 16:18 #77947 | |
GeoffM
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" said:I recall (from my single visit some 3 years ago) there was one from the unused platform line at Chessington onto the line beyond which I understand from a bit of googling was once some sort of yard.Actually I think you're right. Good spot. SimSig Boss Log in to reply |
"Permissive" shunt signals 20/11/2015 at 16:31 #77948 | |
Danny252
![]() 1461 posts |
" said:" said:An error seemingly introduced in the conversion to the loader, it was correctly shown as yellow in scrolly. I would've said it was yellow in Simsig until looking just now! Also applies to SN232 and SN271." said:Sorry, I meant "in a sim". SN120 was the example I linked to earlier, but the sim shows it as a red shunt." said:SN201 is still a yellow shunt, and is set to remain so until Thingley is resignalled in the new year.I'm struggling to find an example of a yellow shunt as they're not that common]There's one in Thingley Yard, visible as you pass in the Up direction. At least it was there last time I went past a few weeks ago. Last edited: 20/11/2015 at 16:32 by Danny252 Log in to reply |
"Permissive" shunt signals 20/11/2015 at 17:20 #77949 | |
JamesN
![]() 1591 posts ![]() |
" said:" said:271! I knew Swindon had a third but the maps at work have all been updated for the resignalling already, couldn't recall the number. Thanks." said:An error seemingly introduced in the conversion to the loader, it was correctly shown as yellow in scrolly. I would've said it was yellow in Simsig until looking just now! Also applies to SN232 and SN271." said:Sorry, I meant "in a sim". SN120 was the example I linked to earlier, but the sim shows it as a red shunt." said:SN201 is still a yellow shunt, and is set to remain so until Thingley is resignalled in the new year.I'm struggling to find an example of a yellow shunt as they're not that common]There's one in Thingley Yard, visible as you pass in the Up direction. At least it was there last time I went past a few weeks ago. Log in to reply |
"Permissive" shunt signals 20/11/2015 at 17:48 #77952 | |
Stephen Fulcher
![]() 2055 posts |
There is one at Keyham near Plymouth too. Without checking them all, which I cannot be bothered to do, I think a lot of them involve ground frames rather than points worked by the panel directly, which has the added level of safety in that the Shunter is on site operating the GF so to take us back to the original query again this adds an added layer of protection in that he can see what is going on in his locality and act accordingly (ie not pull the points with a train about to pass over them). I know Keyham West has lever locks in addition to the release for the frame itself given by the Panel, so the track circuit direct locking Geoff mentioned earlier in the thread applies, as well as any route locking that may be there due to slots on signals etc. Kbarber makes a good point reference local knowledge and experience being replaced by a theoretically foolproof system where these days stop signals tend to be provided, often with another one to get out of the headshunt too, quite often employing opposing locking omitted controls to enable the headshunt to be used without having to keep phoning the panel up all the time. Log in to reply |
"Permissive" shunt signals 20/11/2015 at 17:48 #77953 | |
lazzer
![]() 611 posts |
" said:Sorry, I meant "in a sim".Bristol in '80s mode has one at the southern exit of Malago Vale, to name one we haven't discussed yet. Possibly because it's now a housing estate ... Log in to reply |
"Permissive" shunt signals 20/11/2015 at 17:53 #77954 | |
Jersey_Mike
![]() 250 posts |
" said:My comment was directed at the reason something like OLO was never set up in the first place and yellow shunt signal system was implemented. In North America the alternative to a drill signal is to have a non-interlocked hand throw switch to the siding or to place the signal on the connection between the siding and the main track, leaving the siding points outside of interlocking limits. Last edited: 20/11/2015 at 17:53 by Jersey_Mike Log in to reply |
"Permissive" shunt signals 20/11/2015 at 17:58 #77955 | |
headshot119
![]() 4869 posts |
" said:" said:I much prefer the UK method of a yellow shunt and interlocked point work.My comment was directed at the reason something like OLO was never set up in the first place and yellow shunt signal system was implemented. I don't much fancy someone leaving the hand point set for the main line and something rolling away. "Passengers for New Lane, should be seated in the rear coach of the train " - Opinions are my own and not those of my employer Log in to reply |
"Permissive" shunt signals 20/11/2015 at 18:06 #77956 | |
Izzy
![]() 44 posts |
Yellow shunts were originally installed (at the operations department's request) where a shunt signal was required, but the amount of shunting clear of the main line would be a burden on the signalman (signaller, these days). The signalman would not move the exit points for a move to the main line without being asked to by a shunter or driver (thus no movements would be approaching the signal when this was requested) - or when the signalman had made sure that conflicting movements in the sidings were stopped if something needed to be signalled in (giving rise in some very rare locations, to a green lever that operated a mechanical gong or bell to advise yard staff to stop shunting). Because i am talking about signalman and not signaller, it can be rightly assumed that i am talking about mechanical days on lever frames here. In the 1970's or very early 1980's, it was decreed that a signal MUST be cleared for any movement over an interlocked set of points in new installations. This was the end of new installations of yellow shunts - but the beginning of OLO (opposing locking omitted), which was provided for the same situations that a yellow shunt would have been in the old days - again, at the operations department's specific request. I am not aware of anywhere where this provision has been made because the designer thought it would make things easier for the signaller without being asked - but it may have happened somewhere. Scheme development was never an area i got involved in very much. OLO is provided to this day on new installations - mainly where there is a lot of back and forth shunting in and out of sidings. There are very few places these days that haven't been resignalled to newer standards, so yellow shunts are only going to get rarer. By the nature of where these movements take place, it is rare to see this type of signal as a member of the public - as they are normally quite a way from where they are publicly visible - or facing away from those places. As Geoff says, with SSI data, there is actually more data required to be written for extra conditions - which is in contrast to mechanical signalling where there is no extra locking in the frame, but one less notch to be cut in the mechanical point detection next to the points. I find it quite amusing that a lot of extra wiring or data that needs to be provided in electrical or computerised interlockings was actually provided for free in a mechanical installation. For example, if lever 1 locks lever 2, then lever 2 must lock lever 1 unless something clever is done - as a solid bit of metal will conversely lock in either direction (although there are some very clever ways around this - but swinging tappets and Stowells locks are the topic of a whole new post) - whereas signal 1 will not always automatically conversely lock signal 2 in relay or SSI unless specifically designed to do so. So, as a mechanical designer, it was often the case that by the time you have designed half of the locking, the other half had already been done for you. As for where any survivors remain, i can't think of any off hand - all the ones i knew of on the old southern region have gone now, i think - but i'm sure there are still one or two left somewhere in the country. Log in to reply The following users said thank you: GeoffM, Steamer, kbarber |
"Permissive" shunt signals 20/11/2015 at 18:38 #77957 | |
Lardybiker
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Barnetby Down sidings has a yellow mechanical shunt signal to exit the reception sidings in the up direction. I believe it BE35 (don't have the sim or sim data to hand so I am guessing...if its not BE35 its BE "thirty something"). Did look for a piccy but all I found was piccys of pretty much every Barnetby signal EXCEPT that one, of course!! (sure now I've said that someone will now find it. Log in to reply |
"Permissive" shunt signals 20/11/2015 at 18:44 #77958 | |
AndyG
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At Yeovil Junction, there is/were two shunt discs on adjacent sidings, one red, one yellow. Not particularly clear, but on Danny Scroggins' photos shunt 33 is a yellow disc, shunt 34 a red one. I can only help one person a day. Today's not your day. Tomorrow doesn't look too good either. Log in to reply |
"Permissive" shunt signals 20/11/2015 at 20:07 #77965 | |
Steamer
![]() 3958 posts |
" said:clive said:What you're forgetting is that on a mechanical frame a yellow shunt is implemented in exactly the same way as a normal shunt signal. To have a second shunt signal and OLO, you need to have an extra lever, signal and wire run. Hence the cost savings in using a single yellow shunt signal.This system requires extra interlocking circuitry. The yellow shunt was something that could be installed very simply and cheaply, even in mechanical interlockings. As attitudes have changed, and as interlocking circuits change from "lots of extra relays" to "one line of code", the balance has swung from yellow shunt to OLO.It seems fairly simple to set up on a mechanical frame. " said: At Yeovil Junction, there is/were two shunt discs on adjacent sidings, one red, one yellow.They've been gone for a few years- Basingstoke took over the route in March 2012. " said: Barnetby Down sidings has a yellow mechanical shunt signal to exit the reception sidings in the up direction. I believe it BE35 (don't have the sim or sim data to hand so I am guessing...if its not BE35 its BE "thirty something").It is indeed BE35. Sadly, it has just more than a month left to live before the area is re-signalled over Christmas. Very side-on photo below, taken from platform 4: ![]() Post has attachments. Log in to view them. "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) Log in to reply |
"Permissive" shunt signals 20/11/2015 at 23:23 #77975 | |
Danny252
![]() 1461 posts |
" said:What you're forgetting is that on a mechanical frame a yellow shunt is implemented in exactly the same way as a normal shunt signal. To have a second shunt signal and OLO, you need to have an extra lever, signal and wire run. Hence the cost savings in using a single yellow shunt signal.Assuming you don't mind always clearing the two signals together (and many S&T department didn't), you can do away with that extra lever and wire run! Log in to reply |
"Permissive" shunt signals 20/11/2015 at 23:56 #77976 | |
Izzy
![]() 44 posts |
Also not forgetting that OLO wasn't done (or at least only extremely rarely) on mechanical frames for three reasons. 1. The yellow shunt was standard practice in most parts of the British Isles in this situation for mechanical signals. 2. OLO only really started to be implemented after yellow shunts were made obsolete, normally on power signalling schemes (although some earlier power schemes still used yellow shunts, with a ground signal with a yellow lens instead of a red one, so it showed yellow and white for the "ON" aspect). 3. To remove signal to signal locking in only one of several possible routes for a single signal in a mechanical frame's interlocking requires a very clever mechanical arrangement - you would need to make a lump of metal disappear from the locking tray (or at least be bypassed somehow (i still refuse to go into Stowells locks and swinging tappets in this post hehe - but these are ways to do that)). OLO is far simpler in an electric interlocking, as it just requires a wire to bypass (very simplified) a bit of locking in a specific circumstance. All the mechanical conditional locks are pretty intricate, subject to wear, and not as robust as a full size dog and tappet arrangement. Don't forget that a major part of the design of mechanical interlocking is to prevent a large muscular signalman from breaking it if he incorrectly tries to pull (or push in some cases) a lever when it is locked. Some systems were better than others in this regard, but the conditional locks are all weaker than full size dogs, as they normally provide some sort of escapement and are therefore smaller in order to fit in the same space as a normal locking component. I remember on two occasions, a tester breaking the mechanical locking in the tray as it wasn't robust enough. One of them on a preserved railway (who shall remain nameless) - i really felt sorry for them, as we came along and broke 8 months of their work, but that is what testing is for. Once they realised why things were done in a certain way, the locking was modified (correctly done this time), and the frame went into service - after another brutal session of lever pulling by the tester (who shall also remain nameless). In a mechanical system, the yellow shunt is the easiest and cheapest method to provide for this sort of situation of repeated in and out shunting. In an electrical interlocking, OLO is easier to achieve, arguably cheaper (reduced cost of different signal heads and lenses), and provides the extra benefit of a positive proceed authority to the driver from all directions and routes. In an electronic interlocking, yes there is more data and design required, but the positive proceed aspect for all routes is deemed to be worth the extra hassle. This last bit is educated guesswork on my behalf, but it seems likely to me. Last edited: 21/11/2015 at 00:05 by Izzy Log in to reply |
"Permissive" shunt signals 21/11/2015 at 00:27 #77977 | |
DriverCurran
![]() 685 posts |
In sim yellow shunts... Portsmouth has one controlling exit from Fratton Yard in the up direction (not sure if this survived the PARS) One of my WIP sims also has at least one yellow shunts as well. Paul You have to get a red before you can get any other colour Log in to reply |
"Permissive" shunt signals 22/11/2015 at 20:01 #78058 | |
clive
![]() 2766 posts |
" said:Clive, I hope that this is not an impermanent question. Where were you when you posted your message today?I was in Melbourne. Right now I'm in Sydney, but leaving for Newcastle in the next hour or so. Log in to reply |
"Permissive" shunt signals 22/11/2015 at 20:07 #78059 | |
clive
![]() 2766 posts |
" said:" said:Still requires an extra lever, signal, and wire run.It seems fairly simple to set up on a mechanical frame. Log in to reply |
"Permissive" shunt signals 22/11/2015 at 20:43 #78061 | |
clive
![]() 2766 posts |
" said:On the other hand, you can easily do stuff in electric or electronic locking that's hard in mechanical ones, like conditional protections or swinging overlaps. And, as you sort of point out later, you don't have people pulling the wiring out by accident when they press a button while mechanical locking has to be robust. Swings and roundabouts. Log in to reply |
"Permissive" shunt signals 06/02/2016 at 22:34 #80441 | |
onthehippidyhop
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" said:" said:In the Kent region there are 2 yellow shunt discs at Canterbury West Up Sidings. When I shunt into there, we pass the first one at ON, and stop at the second until it goes to OFF for the platform. I am sure there are more around in this region as well.I'm struggling to find an example of a yellow shunt as they're not that common]There's one in Thingley Yard, visible as you pass in the Up direction. At least it was there last time I went past a few weeks ago. Log in to reply |