Double Slips

[ABB125]

Normally when two tracks cross you'll have a fixed diamond, with 4 gaps at the corners for the flanges. A switched diamond eliminates the gaps allowing higher-speed running but at the cost of essentially being two sets of stub-ended points adjacent to each other, requiring interlocking and point motors. https://upload.wikimedia.org/wikipedia/commons/f/f0/Switchdiamond.jpg

A double slip allows trains on one track to switch to the track crossing at the diamond. Because of the amount of extra metalwork involved (point blades and curved rails), a switched diamond would be very difficult to maintain and inspect. Here's a photo of a double slip with normal diamond: https://upload.wikimedia.org/wikipedia/commons/7/78/Double_slip_at_Munich_central.jpg
Here's a photo of a double slip with swtiched diamond: https://www.pinterest.co.uk/pin/328129522830439800/

Ah ok, thanks!

 

[furnessvale]

Normally when two tracks cross you'll have a fixed diamond, with 4 gaps at the corners for the flanges. A switched diamond eliminates the gaps allowing higher-speed running but at the cost of essentially being two sets of stub-ended points adjacent to each other, requiring interlocking and point motors. https://upload.wikimedia.org/wikipedia/commons/f/f0/Switchdiamond.jpg

A double slip allows trains on one track to switch to the track crossing at the diamond. Because of the amount of extra metalwork involved (point blades and curved rails), a switched diamond would be very difficult to maintain and inspect. Here's a photo of a double slip with normal diamond: https://upload.wikimedia.org/wikipedia/commons/7/78/Double_slip_at_Munich_central.jpg
Here's a photo of a double slip with swtiched diamond: https://www.pinterest.co.uk/pin/328129522830439800/

On the face of it, the angle of the obtuse doesn't seem to be shallow enough to demand the installation of a switch diamond, so why have they gone to all the extra expense and maintenance problems of installing one?

 

[zwk500]

On the face of it, the angle of the obtuse doesn't seem to be shallow enough to demand the installation of a switch diamond, so why have they gone to all the extra expense and maintenance problems of installing one?

I'd love to know, but it's a handy photo to find!

 

[MarkyT]

Normally when two tracks cross you'll have a fixed diamond, with 4 gaps at the corners for the flanges. A switched diamond eliminates the gaps allowing higher-speed running but at the cost of essentially being two sets of stub-ended points adjacent to each other, requiring interlocking and point motors.

As the crossing angles reduce in faster layouts, the flange gaps in preferred fixed diamond crossings get larger and eventually exceed safety limits, necessitating provision of the complex switched variety instead. Unfortunately, those short stub switches are notoriously difficult to maintain in adjustment, with the slightest bit of heat expansion often causing detection failure. Hence they were some of the first bits of infrastructure to receive the white rail painting treatment, which reflects sunlight and limits heat gain.

 

[swt_passenger]

Did Kings Cross have any before its remodelling?

When you asked this we’d just been drifting away for a few posts about three way points, I thought I’d check in case your question was about them?

 

[zwk500]

As the crossing angles reduce in faster layouts, the flange gaps in preferred fixed diamond crossings get larger and eventually exceed safety limits, necessitating provision of the complex switched variety instead. Unfortunately, those short stub switches are notoriously difficult to maintain in adjustment, with the slightest bit of heat expansion often causing detection failure. Hence they were some of the first bits of infrastructure to receive the white rail painting treatment, which reflects sunlight and limits heat gain.

Indeed. I assume that's also why they're being progressively replaced with pairs of crossovers?

 

[Big Jumby 74]

This is for one of you good people who understands the engineering side of track work/maintenance better than I. I appreciate the basics, but more from an operational (train planning angle), as in what could one achieve to maximise train movements with the infrastructure in situ (past tense, now retired, so purely out of interest now).

During the planning stages of the 10 car suburban railway on the South Western (SWT as it was), back in 2014, the lack of stabling capacity (at that time) required some alternative thinking, as in how could certain ECS trains be re-routed to form their a.m. peak start up services, without a complete timetable re-write.
It became clear very early on that the various implications of running 10 car vice 8 car, ECS paths Westbound down the Windsor lines, early morning out of Clapham Yard, were all but utilised. Consequently a revision of ECS Westbound services out of Wimbledon Park was looked in to.
The aim of the latter, specifically, was to find a path for a new ECS out of Wimbledon Park, down via Surbiton and round to Staines to form a morning peak Staines to Waterloo, that had previously been provided from elsewhere.

Now to the crux of the matter: this proposed move would be via the Down Main Fast to Weybridge thence the diamond crossing in the Up Main Fast at Weybridge, to gain access to the Chertsey branch. At this point in time (2014 etc) the said diamond crossing was failing routinely resulting in what seemed like a near permanent TSR (Temporary Speed Restriction) usually about 50 mph, which was recognised as causing enough of a delay to the stream of Up Main Fast trains to have a very real negative impact on the a.m. peak arrivals at Waterloo.

The question was posed, when exactly I do not remember, but to the effect that can the said diamond crossing be done away with altogether (to improve peak train running on the UMFL). The answer from the planners was definite NO, as the new 10 car train service would without doubt need the same in place and working for every SX (week) day part of the service, if not for engineering diversions at weekends.

Consequently the TSR often remained in place thereafter.

Back to the present, and I have no idea what the situation is now, but am curious as to the reasons this diamond could seemingly never be 'gold plated' (maintenance wise), a phrase that may be known to some in relation to the Waterloo-Clapham Jn corridor some years ago. In the planning side it was often jested it was down to poor grade (non UK) steel, but who knows? Never heard or told anything remotely truthful about this from above.

 

[MarkyT]

Indeed. I assume that's also why they're being progressively replaced with pairs of crossovers?

Where the longer junction layout fits, that's an option, or sometimes it might be worth sacrificing junction speed and settling for a fixed diamond. Switched diamonds can still make sense in some new layouts, such as the Bacon Factory curve junctions at Ipswich.

 

[furnessvale]

Indeed. I assume that's also why they're being progressively replaced with pairs of crossovers?

Years ago, 1 in 8 was considered the shallowest safe angle for an obtuse crossing so many double junctions were laid out incorporating these and avoiding switch diamonds. Along came diesels and it was discovered some were not happy with 1 in 8 and 1 in 7.5 was the shallowest safe angle.

Since then, only the most essential double junctions have received switch diamonds. All the others have been relaid with permutations of using 1 in 7.5, or differing uses of single leads in ladders etc.

 

[InOban]

If you're really into slips... This is Zurich. The telephoto makes it even more dramatic.

https://twitter.com/SignaloftheDay/status/1500773765537406976?t=Uo3iXyXJZVmIno23RIaMng&s=09

 

[Western 52]

If you're really into slips... This is Zurich. The telephoto makes it even more dramatic.

https://twitter.com/SignaloftheDay/status/1500773765537406976?t=Uo3iXyXJZVmIno23RIaMng&s=09

Must be a maintenance nightmare, not just for PW but the OLE too!

 

[nlogax]

If you're really into slips... This is Zurich. The telephoto makes it even more dramatic.

https://twitter.com/SignaloftheDay/status/1500773765537406976?t=Uo3iXyXJZVmIno23RIaMng&s=09

That's beautiful. Makes UK trackwork look like it's been through hell..I daresay that Swiss station throat trackwork doesn't receive the same punishment that ours does in terms of scheduled workings.

 

[furnessvale]

Must be a maintenance nightmare, not just for PW but the OLE too!

Almost reaching the stage where the dodgem cars OHLE is the answer. ( A large steel net suspended above the area so that dodgem cars can wander around freely).

 

[matchmaker]

As the crossing angles reduce in faster layouts, the flange gaps in preferred fixed diamond crossings get larger and eventually exceed safety limits, necessitating provision of the complex switched variety instead. Unfortunately, those short stub switches are notoriously difficult to maintain in adjustment, with the slightest bit of heat expansion often causing detection failure. Hence they were some of the first bits of infrastructure to receive the white rail painting treatment, which reflects sunlight and limits heat gain.

I was on an official visit to Dalmuir Park signal box (North Clyde) one hot summer afternoon in the 1970s when the switched diamonds failed due to the heat. It took the combined efforts of the signalman, the district inspector and yours truly to get them cooled down and operating properly. If the DI and myself hadn't been there the signalman would have been on his own! Goodness knows what delays would have been like.

 

[Railsigns]

Some switch diamonds were equipped with water sprinklers, which the signalman would turn on during hot weather.

 

[Annetts key]

Some comments from me…

Heat can affect any S&C/point work, especially where there is CWR/LWR one side or surrounding the junction.

With respect to S&C/point work in Network Rail land being unreliable, part of the problem is that there is insufficient maintenance of the ballast formation. When large heavy duty bolts and nuts vibrate off (even though they were done up to the correct torque specification), you know that the track is voiding (excessive vertical movement as a train passes over).

Unfortunately as the S&C/point work becomes more complex, tamping machines (see more details here) find it harder to maintain the ballast formation. So it has to be done with actual people using the appropriate ‘portable’ tools (normally powered these days). But there is difficulty getting them in during most of the day due to the number of trains. And they are needed everywhere else at night/weekends.

The other problem is not following up and dealing with problems that have been found. Minor problems get noted, but not actioned. Some get worse, and then contribute to the cause of a failure.

And wear is proportional to the amount and type of traffic. But it’s harder to deal with on busy lines… so gets left until it gets to the “it has to done” stage.

And lastly, anything other than bog standard parts are not kept in stock. So when something is discovered to have a problem, if it cannot be repaired, the lead time before a replacement can be made is measured in weeks. Then it has to be planned in to replace it. Which often means other work has to be postponed.

 

[Big Jumby 74]

And lastly, anything other than bog standard parts are not kept in stock. So when something is discovered to have a problem, if it cannot be repaired, the lead time before a replacement can be made is measured in weeks. Then it has to be planned in to replace it. Which often means other work has to be postponed.

I concur with not only your comments here, but also your overall reply. I always found it a shame that those in charge of the purse strings overall often did not understand how in some cases, certain often perceived minor parts of the infrastructure, could, if not maintained correctly, have such an adverse effect on very large parts of the network.

 

[Bald Rick]

What's the difference between a double slip and a switch diamond?

ones a nightmare to maintain, and the other is 3 times harder.

This is for one of you good people who understands the engineering side of track work/maintenance better than I. I appreciate the basics, but more from an operational (train planning angle), as in what could one achieve to maximise train movements with the infrastructure in situ (past tense, now retired, so purely out of interest now).

During the planning stages of the 10 car suburban railway on the South Western (SWT as it was), back in 2014, the lack of stabling capacity (at that time) required some alternative thinking, as in how could certain ECS trains be re-routed to form their a.m. peak start up services, without a complete timetable re-write.
It became clear very early on that the various implications of running 10 car vice 8 car, ECS paths Westbound down the Windsor lines, early morning out of Clapham Yard, were all but utilised. Consequently a revision of ECS Westbound services out of Wimbledon Park was looked in to.
The aim of the latter, specifically, was to find a path for a new ECS out of Wimbledon Park, down via Surbiton and round to Staines to form a morning peak Staines to Waterloo, that had previously been provided from elsewhere.

Now to the crux of the matter: this proposed move would be via the Down Main Fast to Weybridge thence the diamond crossing in the Up Main Fast at Weybridge, to gain access to the Chertsey branch. At this point in time (2014 etc) the said diamond crossing was failing routinely resulting in what seemed like a near permanent TSR (Temporary Speed Restriction) usually about 50 mph, which was recognised as causing enough of a delay to the stream of Up Main Fast trains to have a very real negative impact on the a.m. peak arrivals at Waterloo.

The question was posed, when exactly I do not remember, but to the effect that can the said diamond crossing be done away with altogether (to improve peak train running on the UMFL). The answer from the planners was definite NO, as the new 10 car train service would without doubt need the same in place and working for every SX (week) day part of the service, if not for engineering diversions at weekends.

Consequently the TSR often remained in place thereafter.

Back to the present, and I have no idea what the situation is now, but am curious as to the reasons this diamond could seemingly never be 'gold plated' (maintenance wise), a phrase that may be known to some in relation to the Waterloo-Clapham Jn corridor some years ago. In the planning side it was often jested it was down to poor grade (non UK) steel, but who knows? Never heard or told anything remotely truthful about this from above.

that’s another pig of a junction. Hammered by heavy Siemens trains all day (to a much greater extent than anything beforehand). very difficult to keep in line, and has to be done by hand. All on timber -IIRC a concrete solution (which is much more stable) simply couldn’t be designed.

If you're really into slips... This is Zurich. The telephoto makes it even more dramatic.

https://twitter.com/SignaloftheDay/status/1500773765537406976?t=Uo3iXyXJZVmIno23RIaMng&s=09

that will give a track maintenance engineer nightmares!

 

[Class 170101]

When you asked this we’d just been drifting away for a few posts about three way points, I thought I’d check in case your question was about them?

Double slips, I don't think Kings Cross had any three way points did it?

 

[swt_passenger]

Double slips, I don't think Kings Cross had any three way points did it?

No, I just thought it was possibly worth asking, in case that was your real question…

 

[mr_moo]

If you're really into slips... This is Zurich. The telephoto makes it even more dramatic.

https://twitter.com/SignaloftheDay/status/1500773765537406976?t=Uo3iXyXJZVmIno23RIaMng&s=09

Wow. that is definately impressive. As others have said, a sure nightmare to maintain but the operational flexibility that will offer is great, and that photo is awesome!

== Doublepost prevention - post automatically merged: 7 Mar 2022 ==

Strange - only yesterday I watched a video on YouTube about three-way points; going from a single line to three lines at the same point. Are there any of these in the UK network?

Quite often you'll find these are three directional points, but they aren't quite all going from the same point. They are essentially interlaced points. The above references one from southampton is this type - if you follow the switch rails you'll essentially see two 'toes' a short distance apart:




This one in Acton yard is similar:

Google Maps

Find local businesses, view maps and get driving directions in Google Maps.

goo.gl

Again, you can see it's essentially two sets of S&C on top of each other, with two distinctly separate toes:



There certainly used to be proper 3-throws around, where all three routes do converge pretty much at the toe, although I'm not aware of any left in operational areas, not that my knowledge of sidings etc is particularly comprehensive!

 

[AlbertBeale]

Wow. that is definately impressive. As others have said, a sure nightmare to maintain but the operational flexibility that will offer is great, and that photo is awesome!

== Doublepost prevention - post automatically merged: 7 Mar 2022 ==


Quite often you'll find these are three directional points, but they aren't quite all going from the same point. They are essentially interlaced points. The above references one from southampton is this type - if you follow the switch rails you'll essentially see two 'toes' a short distance apart:
View attachment 111151



This one in Acton yard is similar:

Google Maps

Find local businesses, view maps and get driving directions in Google Maps.

goo.gl

Again, you can see it's essentially two sets of S&C on top of each other, with two distinctly separate toes:

View attachment 111152

There certainly used to be proper 3-throws around, where all three routes do converge pretty much at the toe, although I'm not aware of any left in operational areas, not that my knowledge of sidings etc is particularly comprehensive!

The 2nd and 9th photos here (https://www.rmweb.co.uk/community/index.php?/topic/42395-train-ferry-at-messina-sicily/) seem to show genuine 3-way points, on the ramp to the train ferry on the way to Sicily.

 

[bspahh]

If you're really into slips... This is Zurich. The telephoto makes it even more dramatic.

https://twitter.com/SignaloftheDay/status/1500773765537406976?t=Uo3iXyXJZVmIno23RIaMng&s=09

I couldn't see the buildings in the image in the aerial photographs on Google Maps. I stayed in the 25 Hours hotel near there a couple of years ago, and it was all fairly new then.
This is a schematic diagram of the tracks into Zürich HB from

http://www.sporenplan.nl/html_nl/sporenplan/sbb/zuerich-winterthur.html

 

[buz33]

Double slips, I don't think Kings Cross had any three way points did it?

No, I just thought it was possibly worth asking, in case that was your real question…

The old KGX layout is still shown on Google Maps and that suggests that there were 3 way points on the entrance to Gasworks tunnel (also 5 double slips).

Google Maps

Find local businesses, view maps and get driving directions in Google Maps.

www.google.com

 

[swt_passenger]

The old KGX layout is still shown on Google Maps and that suggests that there were 3 way points on the entrance to Gasworks tunnel (also 5 double slips).

Google Maps

Find local businesses, view maps and get driving directions in Google Maps.

www.google.com

Yes, I was originally trying to establish what the question in post #82 was definitely asking about. The 3 way interlaced points at Kings Cross seem to have been relatively unknown, all the “improvements in maintenance” PR and discussions never seem to mention them.

Is it possibly because although they’re fairly unusual, (and pretty complex looking), they aren‘t such a maintenance nightmare?

 

[Bald Rick]

Yes, I was originally trying to establish what the question in post #82 was definitely asking about. The 3 way interlaced points at Kings Cross seem to have been relatively unknown, all the “improvements in maintenance” PR and discussions never seem to mention them.

Is it possibly because although they’re fairly unusual, (and pretty complex looking), they aren‘t such a maintenance nightmare?

Three throw points are less of a maintenance liability than switch diamonds. The issue with three throws is that they are all bespoke, so any failures of crossing components usually means a rapid phone call to Beeston and an emergency order for a special casting.

 

[swt_passenger]

Three throw points are less of a maintenance liability than switch diamonds. The issue with three throws is that they are all bespoke, so any failures of crossing components usually means a rapid phone call to Beeston and an emergency order for a special casting.

Thanks Bald Rick, that‘s what I was thinking but I thought I’d await an expert…

 

[TSG]

This is for one of you good people who understands the engineering side of track work/maintenance better than I. I appreciate the basics, but more from an operational (train planning angle), as in what could one achieve to maximise train movements with the infrastructure in situ (past tense, now retired, so purely out of interest now).

During the planning stages of the 10 car suburban railway on the South Western (SWT as it was), back in 2014, the lack of stabling capacity (at that time) required some alternative thinking, as in how could certain ECS trains be re-routed to form their a.m. peak start up services, without a complete timetable re-write.
It became clear very early on that the various implications of running 10 car vice 8 car, ECS paths Westbound down the Windsor lines, early morning out of Clapham Yard, were all but utilised. Consequently a revision of ECS Westbound services out of Wimbledon Park was looked in to.
The aim of the latter, specifically, was to find a path for a new ECS out of Wimbledon Park, down via Surbiton and round to Staines to form a morning peak Staines to Waterloo, that had previously been provided from elsewhere.

Now to the crux of the matter: this proposed move would be via the Down Main Fast to Weybridge thence the diamond crossing in the Up Main Fast at Weybridge, to gain access to the Chertsey branch. At this point in time (2014 etc) the said diamond crossing was failing routinely resulting in what seemed like a near permanent TSR (Temporary Speed Restriction) usually about 50 mph, which was recognised as causing enough of a delay to the stream of Up Main Fast trains to have a very real negative impact on the a.m. peak arrivals at Waterloo.

The question was posed, when exactly I do not remember, but to the effect that can the said diamond crossing be done away with altogether (to improve peak train running on the UMFL). The answer from the planners was definite NO, as the new 10 car train service would without doubt need the same in place and working for every SX (week) day part of the service, if not for engineering diversions at weekends.

Consequently the TSR often remained in place thereafter.

Back to the present, and I have no idea what the situation is now, but am curious as to the reasons this diamond could seemingly never be 'gold plated' (maintenance wise), a phrase that may be known to some in relation to the Waterloo-Clapham Jn corridor some years ago. In the planning side it was often jested it was down to poor grade (non UK) steel, but who knows? Never heard or told anything remotely truthful about this from above.

I'm afraid I don't know the reason why the crossing was so problematic, although I think the angle of a crossing can limit your options in terms of construction and it did look an odd angle. I don't know the details but I think they may have tweaked the layout a bit to use a different part (presumably something more maintainable) a few months ago when they changed it. Quite a big possession with a lot of work going on. I know the work was brought forward to get rid of the TSR.

 

[Dave_Cardboard]

Quite often you'll find these are three directional points, but they aren't quite all going from the same point. They are essentially interlaced points. The above references one from southampton is this type - if you follow the switch rails you'll essentially see two 'toes' a short distance apart:

Aren't they called "tandem" switches in UK parlance...? As opposed to "true" three-throw switches with common toe points.

 

[furnessvale]

Aren't they called "tandem" switches in UK parlance...? As opposed to "true" three-throw switches with common toe points.

Correct in both cases. "Three throw" switches are even more frowned upon as, according to "British Railway Track", it is impossible to maintain gauge through the switches when they are set for the middle road.

Never having had the need to design such switches, I will take their word for it.