Wide to Gauge Trap Points

[alexgoei]

Hello PJW,

Please see the attached.

Is my interpretation of the symbol with respect trapping a runaway train (represented by the direction of travel) correct?

Look forward to your reply please

Thank you

Regards


Alex

[Zaphod]

Hello PJW,

Please see the attached.

Is my interpretation of the symbol with respect trapping a runaway train (represented by the direction of travel) correct?

Look forward to your reply please

Thank you

Regards


Alex

I don't think your direction of travel is the right way round. Wide-to-gauge trap points appear to branch out into a 'Y' shape in the direction of travel, presenting a gap for the train to fall into (at low speed). I assume the symbol seeks to replicate this arrangement to some extent, so that when viewed in the direction of travel it appears a bit like a 'Y', as the real version does.

That's my understanding anyway.

As an aside, I also assume that this type of trap point is capable of being run through (assuming appropriate point machine) so would have no trapping effect on 'wrong' direction trains. Can anyone confirm or deny this?

- ZB

[Peter]

I don't think your direction of travel is the right way round. Wide-to-gauge trap points appear to branch out into a 'Y' shape in the direction of travel, presenting a gap for the train to fall into (at low speed). I assume the symbol seeks to replicate this arrangement to some extent, so that when viewed in the direction of travel it appears a bit like a 'Y', as the real version does.

That's my understanding anyway.

As an aside, I also assume that this type of trap point is capable of being run through (assuming appropriate point machine) so would have no trapping effect on 'wrong' direction trains. Can anyone confirm or deny this?

- ZB

I agree with you that it is the movement in the other direction to that shown by Alex which would be trapped.

Bear in mind that, like all trap points, there may be legitimate moves over them in the direction that they are designed to trap (eg at the end of a bi-directional loop) hence they will be worked as opposed to those which do not (at the "in" end of a unidirectional loop) which could therefore be trailable spring points.

A typical place where wide to gauge traps may be used is a spur siding in between two running lines. This would mean that there are legitimate moves both ways.

[alexgoei]

Dear Peter and Zaphod,

Thank you for your reply.

I was trying to find schemes in the Study Pack with this symbol but could not. I did find an actual picture of a wide to gauge trap point at Clapham junction but what was shown on the schematic did not use the Network Rail symbol.

I suppose it is when site constraints do not allow trapping into the cess, some trapping is better than no trapping at all. Incidentally the example shown at Clapham Junction is between two running lines. From the picture, the site is tight. In the IRSE CD look under Module 2, Power Point, Points for the picture.

Cheers

Alex

[PJW]

Dear Peter and Zaphod,

Thank you for your reply.

I was trying to find schemes in the Study Pack with this symbol but could not. I did find an actual picture of a wide to gauge trap point at Clapham junction but what was shown on the schematic did not use the Network Rail symbol.

I suppose it is when site constraints do not allow trapping into the cess, some trapping is better than no trapping at all. Incidentally the example shown at Clapham Junction is between two running lines. From the picture, the site is tight. In the IRSE CD look under Module 2, Power Point, Points for the picture.

Cheers

Alex

Wide to gauge- independent switches

I couldn't find a proper Signalling Plan depicting Clapham Junction, so I just put a copy of the "5 mile diagram" in the pack to show the track layout and give the idea that each of the switches is driven independently by its own point machine. When both are normal then the wheels attempt to ride on the two fixed stock rails but as these spread the wheels fall off and the train is left, hopefully upright, with each of the wheels between the switch rail and the stock rail.

To signal out of the siding one way then reverse one switch and it looks (to the train wheels at least as a normal set of points; to go out the other way then it is the other switch rail moved to revese and the first one back normal. Never want both switch rails to be reverse at the same time; so a very good case for point-to-point locking.

The issue is that there is no real "straight rail". In truth the TCIs needs to be on the outside of the switch rails. It is not possible realistically to represent the arrangement using a single line to represent a pair of rails, particularly when the rails aren't actually in pair, if you get my drift. Hence has to be a bit abstract, conceptual only, representation.

I have drawn a symbol that I have seen used (to be honest I have no idea how many such points exist on NR but I'd be surprised if there were as many as 25 on the entire network and almost certainly the symbols vary reflecting the old BR rgins and pre-1948 railway companies!) within a post I made last night re the 2005 layout . Not sure if this is the official NR symbol (actually I am not even sure that there is one!) but I am sure it is good enough for the exam; it needs to convey to the examiner that you know what the site arrangement is- if they know that you know then it is good enough.

The other thing to point out is the 2005 Module 3 layout has a Goods Loop with such points at each end of it; this actually does not show the ficticious straight rail as I have but has the TCI shown between the two switches. To me, this is actually even more of a "lie" than my version and it is hard to show that the TCI would be clear of the normal passage of trains. Actually, thinking about it now, it might be best if my symbol had shown a dotted rather than solid straight line on which to mount the TCI- this would get across the idea that it was "virtual" rather than real running rails.


Wide to gauge- switches operating in anti-phase

The symbol shown in what was RT/EC/11004 (no doubt got a different prefix in the new NR L3 series but still ????110004) and reproduced by Alex is a DIFFERENT TYPE of wide to gauge trap, This is basically similar to that described above but the stock rails are wide to gauge and only continue for a short distance. On these points there is however a straight route and to take it BOTH the switches are placed against their respective stock rails and the continuation of these switches just becomes the normal running line. They are operated by a single machine BUT work in antiphase to each other by means of some crank arrangement; as one switch moves to the left then the other moves to the right- obviously these do not have any stretcher bars. They can be operated by clamp-locks but the arrangement is peculiar in that the rams aren't actually connected to where you'd expect them to be.
The use of this type of wide to gauge trap point could be inserted in the running line at the bottom of a steep gradient (the set I remember were on the flyover near Ilford station where one running line has a steep graient and bridge and then drops down to take a different position amongst the width of parallel tracks)- this was really a bit more like a catch point.

Also I believe are sometimes used to give trapping at the exit line of a rolling stock depot. The difference to the situation on the plan discussed is that there is
a single exit "through the middle" of the wide to gauge stub rails,
rather than
a siding that is between two running lines and could have been given two separate crossovers to leave firstly to the left and thereafter to the right (the second having a conventional trap point), but to save length the two crossovers have been merged into one unit and so has a dual role as a crossover for the one exit whilst being the trap for the other exit and vice versa.

I don't believe that either of the above are trailable; like other UK points (other than handpoints in depot and Train Operated Points on some very low density, slow rural lines) should they be trailed by a train then severe damagre can result.

So if you were not confused before, you probably are now.......

[alexgoei]

Dear PJW,

Based on what you are saying, RT/E/C/11004 A3 Switches & Crossings, 12 Trap Points, Wide to Gauge is really a Catch Point rather than a Trap Point?

Cheers

Alex

[PJW]

Dear PJW,

Based on what you are saying, RT/E/C/11004 A3 Switches & Crossings, 12 Trap Points, Wide to Gauge is really a Catch Point rather than a Trap Point?

Cheers

Alex

Indeed it is the symbol for the type of point in which rails work in anti-phase which could be used as a catch or as a trap.
It certainly does not seem applicable to the "two independent switch rail" type, but there does not seem to be an official symbol for this.

[alexgoei]

Hello PJW,

Had a look at the 2005 M3 layout. I will use that.

Cheers

Alex

[Jerry1237]

Remember the differences between traps and catch points though. They are not synonimous terms!

A basic description I've been given is that a trap is there to stop a train conflicting in the expected direction of travel. Catch points are there to stop trains running away in the incorrect direction.

Traditional catches were open as normal and the switch rail was forced against the stock rail by the train. This then sprung back to the open position when a train was absent.

Traps are also normal open but are driven reverse and back to normal again.

Jerry

Dear PJW,

Based on what you are saying, RT/E/C/11004 A3 Switches & Crossings, 12 Trap Points, Wide to Gauge is really a Catch Point rather than a Trap Point?

Cheers

Alex

Indeed it is the symbol for the type of point in which rails work in anti-phase which could be used as a catch or as a trap.
It certainly does not seem applicable to the "two independent switch rail" type, but there does not seem to be an official symbol for this.

[Alasdair]

We use them on the Underground for centre turnback sidings, for example at Rayner's Lane. The neat part is that each switch rail is paired with a point forming the other half of a crossover from the running line, so 2 levers control 4 point machines in three switches. As Peter mentioned above it makes the point to point locking nice and easy, and sorts out flank protection too. Each numbered pair locks the other normal, so three states are possible; 1) both normal = through running, and siding trapped, 2) Entry crossover reverse & exit direction line locked for through running, 3) Exit crossover reverse & entry direction line locked for through running.