LGB 12260 double slip in operation

[curtis]

I have a nickel-silver one, picked up for a sweet price when LGB's UK importer went bust several years ago. Set at ground level amid ballast, I have to be careful that stray bits of granite don't get stuck in the moving parts, but I have to say it is very good at what it does, giving very flexible access to a yard from both running lines, plus a crossover for running around, all in a very small space. It is quite literally central to many train movements and was a bit of a leap of faith when I planned to use it. Routes are selected by using the two point drives in different combinations and I use an EPL boost to ensure a good clunk. Operation is reliable and the 'dead spot' performance under track power is slightly better than an R1 point, for short wheelbase locos; battery ones of all types use it with no problem at all and slow propelling across it seems fine too. Pictured here during the 2021 relaying.
View attachment 312394

This looks like a fantastic junction layout! Do you have a link to your track plan? I'd love to see it in full!

 

[viaEstrecha]

This looks like a fantastic junction layout! Do you have a link to your track plan? I'd love to see it in full!

The slip is P4/P5, bottom centre.

 

[Gizzy]

I have a DS currently out of use, but I'm planning to re-use it on my layout soon.

In its original position, I was using it as a crossover and I 'locked' it for just the straight roads. it was lifted once I'd obtained a diamond crossing.

I'll be using manual levers rather than point motors as its new site will be closer to the marshalling yard....

 

[Andrew_au]

In terms of routes - below is how I "explode" the double slip in my head (ignore the specific geometries/product codes). As @ebay mike said, you can go straight or diverse but the thing to highlight is the straight also includes an X crossing.
View attachment 312401

The other way of thinking about a double slip is to take a ladder junction (two facing turnouts) and slide the two turnouts closer until they overlap. Your abstraction explains the mechanical complexity (e.g. why are there four sets of point blades rather than just two?), but thinking about it as two distinct turnouts crammed together helps model why only a single route can be active through the junction at a time.

Looking at the upper picture above, the trick one needs to remember is that the motor on the right controls which track is active on the left, and vice-versa.

The main (only?) advantage of a double slip over a ladder is that it takes a heck of a lot less room. Not only does the ladder need two distinct turnouts, but also enough separation to protect against the reverse curve that would otherwise result from the crossing track.

Another interesting tidbit:

• A ladder junction requires 2 crossings (one on each turnout)
• A double slip requires 4 crossings
• A double crossover (2nd picture) requires 8 crossings (four on the diamond crossing, and one on each turnout)

 

[dunnyrail]

The other way of thinking about a double slip is to take a ladder junction (two facing turnouts) and slide the two turnouts closer until they overlap. Your abstraction explains the mechanical complexity (e.g. why are there four sets of point blades rather than just two?), but thinking about it as two distinct turnouts crammed together helps model why only a single route can be active through the junction at a time.

Looking at the upper picture above, the trick one needs to remember is that the motor on the right controls which track is active on the left, and vice-versa.

The main (only?) advantage of a double slip over a ladder is that it takes a heck of a lot less room. Not only does the ladder need two distinct turnouts, but also enough separation to protect against the reverse curve that would otherwise result from the crossing track.

Another interesting tidbit:

• A ladder junction requires 2 crossings (one on each turnout)
• A double slip requires 4 crossings
• A double crossover (2nd picture) requires 8 crossings (four on the diamond crossing, and one on each turnout)

One of the reasons why BR went over to what was known as ‘single lead junctions‘ was not just cost but the simplification of servicing those junctions. With s4 simple points a double track to double track Junction can be created from 4 simple points (turnouts) with the junction route having a short bit of single track. Only issue is that of protection as the Bellgrove Crash amongst others showed the short sightedness of inadequate allowance. Bit over the top for our trains but interesting to follow the real thing where we can to protect out little small scale passengers.

Bellgrove train crash driver to sue BR

THE TRAIN driver blamed for last year's Bellgrove crash in Glasgow, in

www.heraldscotland.com

 

[curtis]

The other way of thinking about a double slip is to take a ladder junction (two facing turnouts) and slide the two turnouts closer until they overlap. Your abstraction explains the mechanical complexity (e.g. why are there four sets of point blades rather than just two?), but thinking about it as two distinct turnouts crammed together helps model why only a single route can be active through the junction at a time.

Looking at the upper picture above, the trick one needs to remember is that the motor on the right controls which track is active on the left, and vice-versa.

The main (only?) advantage of a double slip over a ladder is that it takes a heck of a lot less room. Not only does the ladder need two distinct turnouts, but also enough separation to protect against the reverse curve that would otherwise result from the crossing track.

Another interesting tidbit:

• A ladder junction requires 2 crossings (one on each turnout)
• A double slip requires 4 crossings
• A double crossover (2nd picture) requires 8 crossings (four on the diamond crossing, and one on each turnout)

That's a really fair point actually, A Andrew_au

I guess the real way of capturing the only the available routes would be something more like this (without acknowledging the implications of the reverse curve):

 

[Andrew_au]

I recently replaced a LGB angled crossover with a double slip, mostly because I'm a sucker for fancy looking track work, but also because it's a drop-in replacement rather than redesigning the track to support a ladder. This did require introducing a reversing section as I was previously running the two tracks at opposite polarities; the double slip provided a mechanism for turning trains around at which point I could no longer assume a distinct polarity for the every point of the layout.

If one is running track power, the double slip has a subtle advantage over a diamond crossing. On an LGB diamond crossing, both the V and K crossing are fully insulated. On the double slip, only the V crossings are insulated; the K crossings are fully powered. This works because the double slip requires that all four tracks have the same polarity (check out Curtis' ladder junction picture if you need convincing) and thus all tracks meeting at a K crossing are of the same polarity. In contrast, a regular diamond crossing puts no polarity requirements on the crossing vs through track and thus the K frogs must be insulated. This double slip thus reduces the chance of losing electrical power as compared to a diamond crossing.

A diamond crossing could have powered K frogs if it was guaranteed that both tracks had the same polarity. But the two classic uses for a diamond crossing - a double-track junction or a figure-8 - generally mandate opposite polarities (or even independent power circuits).

In prototypical railroads, track crossings are points of significant wear. This isn't nearly as much of an issue on model railroads. Our cars are usually relatively much lighter, and some junction manufacturers (e.g. LGB) cheat by supporting the flanges as the wheels run over the crossing.

 

[Rhinochugger]

Getting my head around the routes available is what's troubling me!

There are only four routes, in two pairs, and they can be controlled by one actuator. It's easy to overthink it.

The only routes available are:

1. Straight through top right to bottom left
2. Straight through top left to bottom right
3. Curve through top right to top left
4. Curve through bottom left to bottom right

Routes 1&2 have the blades in the same position - straight
Routes 3&4 have the blades in the same position - curved

So it can all be controlled - in theory - with one actuator (Just under 50 years ago I had an N gauge Minitrix double slip with one point motor )


Seeeeeemples

 

[Rhinochugger]

I appear to have come into some overt criticism with my photo post of the double slip at Didcot Railway Centre. It was intended to show a double slip in a real world environment, as an aside to the thread topic. It was not intended to be a comparison or instruction of how a toy/model/hobbyist double slip should operate. I accept that there are differences.

David

It's a sensible and useful comparison - and yes, in our toy world we wouldn't necessarily want to do it like that.

 

[Gizzy]

One of the reasons why BR went over to what was known as ‘single lead junctions‘ was not just cost but the simplification of servicing those junctions. With s4 simple points a double track to double track Junction can be created from 4 simple points (turnouts) with the junction route having a short bit of single track.

The single lead junctions at Haughley in Suffolk, and Ely North now constrain operations of freight trains to/from Felixstowe, as these cannot pass on the junctions due to the short section of single line running. These often 30+ wagon trains have to be carefully timetabled, as holding these at a red signal incurs delays due to slowing, stopping and re-starting.

Hence, there are now plans to make these double lead junctions and remove these 'bottlenecks' along the route. One example is the recently completed Werrington underpass near Peterborough....

Werrington Dive Under - Wikipedia

en.wikipedia.org

 

[Andrew_au]

as these cannot pass on the junctions due to the short section of single line running.

Clarifying to make sure I have it straight:

(Note: using Au / UK layouts with up on left and down on right)

Double Junction (with or without ladder)

• Train A-E will block D-B, but can still operate F-B
• Train D-B will block A-E (and obviously F-B), but can still operate A-C

Thus with a double junction, it is always possible to operate two trains (one in each direction) through the junction, although the first route may limit the second.


Single Lead Junction

• Train A-E will block D-B and F-B
• Train D-B will block A-E, but can still operate F-B

With a single lead junction, any operation involving A-E will block all lines (and A-E will be blocked by any other operation).

Flyover
A flyover looks schematically like a double junction, except that A-E and D-B do not intersect. Both lines can be fully utilised, because A/C/E do not interact with B/D/F.

Example
Three trains approach the junction: A going A-E, D going D-B, and F going F-B.

• Double junction: A-E and F-B can proceed, D-B waits
• Single junction: only one of A-E, D-B and F-B can proceed at a time, 2 trains wait
• Flyover: A-E can proceed, as can either of D-B and F-B

Collision risks
It looks to me that a ladder junction is technically slightly less safe than a double junction. The double junction has two possibilities of collision:

• Merge between D-B and F-B
• Crossing between A-E and D-B

The ladder junction offers a third possibility of failure:

• Train from A running onto D or train from D running onto A

This third possibility is interesting because it allows a collision between a single train moving through the junction and a stationary train not in the junction. This does require a signalling / turnout failure and not just SPAD.

The single lead junction introduces the additional risk that a train going A-E could collide with a train going F-B.

Flyovers reduce the collision risk to the single D-B and F-B merge.

 

[dunnyrail]

You are correct in your assumptions.

 

[Paul M]

The Hitchin to Cambridge junction with the Liverpool St to Cambridge line is a double junction without a ladder, always a small worry when travelling the wrong way on the down line

 

[Rhinochugger]

The Hitchin to Cambridge junction with the Liverpool St to Cambridge line is a double junction without a ladder, always a small worry when travelling the wrong way on the down line

Yep, they seem to be a favourite of the old ER - but it may be that traffic demands elsewhere have meant earlier changes. Gizzy's post spoke of a 'dive under', but at Wimbledon, the up suburban line was put on a flyover to avoid conflicting train movements back in 1936.

South West suburban services into Waterloo were all electric by 1920 - so driver only operation (where possible) could have happened over 100 years ago

 

[Gizzy]

The Hitchin to Cambridge junction with the Liverpool St to Cambridge line is a double junction without a ladder, always a small worry when travelling the wrong way on the down line

This junction looks like it will be upgraded, due to construction of the new Cambridge South station at Addenbrookes Hospital and the 'Varsity' line (East West Rail).

Noticed recently that the site works for the new station has started and that some land further south has been cleared....

 

[dunnyrail]

This junction looks like it will be upgraded, due to construction of the new Cambridge South station at Addenbrookes Hospital and the 'Varsity' line (East West Rail).

Noticed recently that the site works for the new station has started and that some land further south has been cleared....

I believe the so called Cambridge South Station with its 4 platforms is likely to be a decade before the Varsity gets built judging by the current process. Though there is supposed to be an announcement re the route between Bedford and Cambridge this ‘Spring’, but I am not holding my breath on the announcement appearing any time soon. Except for possibly a ‘paused’ announcement much like HS2 Euston Station. EDIT announcement expected in May apparently.