Why do some catch points derail 1 side and others on 2?

[bubbles2]

See picture below of the loops at Hemerdon, note the difference of the catch points on the up and down loops.

 

 

https://flic.kr/p/DstEMu

 

 

[Fat Controller]

See picture below of the loops at Hemerdon, note the difference of the catch points on the up and down loops.

 

 

https://flic.kr/p/DstEMu

Could it be that the left-hand one is intended to derail wagons that have run back, and so have relatively little momentum, whilst the right-hand one is to stop a loco (and its train) that has started against signal, or has suffered a brake problem, and can't stop?

[Mike Storey]

Their purpose is to derail a train away from the direction of any possible conflict with another train.

 

So, in your picture, the running lines appear to be on a gradient, where up is away from the camera. So the loop catchpoint on the right will derail a runaway (or a train accidentally passing the controlling signal at danger) away from the through track (on which the 37 is passing). The catch point on the left is design to derail a train, most probably one rolling backwards due to a breakaway or failed brakes, away from the other through line, into the cess on that side..

[keefer]

IIRC the left hand one is a catch point as a precautionary measure against runbacks (for whatever reason)

whereas the right hand one is a trap point which is a regulatory requirement to protect the main running line (esp if it is a passenger line)

[Swindon 123]

IIRC the left hand one is a catch point as a precautionary measure against runbacks (for whatever reason)

whereas the right hand one is a trap point which is a regulatory requirement to protect the main running line (esp if it is a passenger line)

I don't think there was a hard and fast rule as on the North & West between Newport and Shrewsbury, although the majority of exit traps where the double rail type the one at Wooferton was a single rail type at the exit.

 

 

Paul J.

[Derekstuart]

I asked this question a little while back and I think the general consensus was that in antiquity 2 blades- both pointing away from adjacent running line- is normal now, although some examples of single blade can still be found, these are not generally used any more.

 

There is also the "wide to gauge" type where it is exactly symmetric and this is used where there is a running line on both sides, with the idea that the train/vehicle just derails in a straight line.

[The Stationmaster]

Normal GWR practice seems to have been to use singe switch trap points except where there was a  clearly identified need to do the job more comprehensively and reliably it which case two switch rails (usually referred to as 'tongues' in Western speak were provided.  The latter seem to have been most common on lines where passenger stock was stabled but I've never come across any sort of hard & fast ruling in any of the relevant minute books.  and of course in some cases - the well known Bodmin shed situation being a good example - there wasn't really room to provide two tongues or providing two would have got more complicated and expensive.

 

And of course many of these older examples of practice continued well into BR days and, as at Woofferton, even finished up with power operation.

 

With catch points the situation has always been different as single tongued was the norm with two tongues/switch rails only being provided in special/exceptional circumstances on all Companies/Regions.

 

Hemerdon is ('was' to be correct) in some ways an illustration of both practice and change over the years.  The Up Loop (on the left) has a single tongue catchpoint although interestingly it is worked - off the point machine driving the facing connection into the loop - and is protected by a STOP board in the loop.  Quite why it was arranged like that I'm not entirely sure as I don't know if the crossover west of the loop was retained after resignalling in 1973 but it would make some sense if that crossover had remained.

 

The trap point in the Down Loop (on the right) is double tongued very obviously to ensure that any train/loco passing over it errantly would definitely finish up being directed into the bank while being kept clear of the Down Main so a good example of using a double tongue trap instead of a single tongue.

[Derekstuart]

Mike,

 

surely normal GWR practice was to look at whatever other railways were doing and then do the opposite.

[martin_wynne]

A single-blade/tongue catch point cannot change the direction in which a vehicle is moving, it simply dumps it off the rails. Double-blade/tongue catch points can change and deflect the direction of movement away from the running line. The choice therefore depends on the geometry of the location, likely speed, available space, and the price of kippers.

 

These physical objects are/were known to p.w. staff as catch points. Their function is known to operating staff as trap points. (Just pre-empting the usual argument yet again. )

 

Martin.

[Derekstuart]

Presumably the decision whether or not to put an additional rail in the middle to stop it wandering too far off the track was likewise depends upon the same criteria as Martin's post above.

 

Martin

Can you post your comments above a second time please? I want to click useful/informative for the info and also funny for the comment about the inevitable catch/trap argument.

[bubbles2]

Thanks for all the replies, its all useful information.

 

The following pictures show that even with a 2 blade/tongue catch point, there's no guarantee that errant vesicles will come to rest fully clear of the running line.

 

[/url]150261 and 66063 Lostwithiel by Andy Hoare, on Flickr">http://150261 and 66063 Lostwithiel by

[/url]150261 and 66063 Lostwithiel by Andy Hoare, on Flickr">Andy Hoare, on Flickr

 

[/url]">http://

 

[/url]">http://http://s62.photobucket.com/user/Debe2233/media/Lostwithiel%20off%20the%20road%2023%207%202014/DSC_0752_zps346759a3.jpg.html'>

[The Stationmaster]

Presumably the decision whether or not to put an additional rail in the middle to stop it wandering too far off the track was likewise depends upon the same criteria as Martin's post above.

 

Martin

Can you post your comments above a second time please? I want to click useful/informative for the info and also funny for the comment about the inevitable catch/trap argument.

 

I put the 'funny' for you on Martin's post  (troublesome lot those PWay wallahs - some of them have a limited understanding of railway operating and they even get upset when the operators blame their track for derailing trains unintentionally)

[Dunsignalling]

A single-blade/tongue catch point cannot change the direction in which a vehicle is moving, it simply dumps it off the rails. Double-blade/tongue catch points can change and deflect the direction of movement away from the running line. The choice therefore depends on the geometry of the location, likely speed, available space, and the price of kippers.

 

These physical objects are/were known to p.w. staff as catch points. Their function is known to operating staff as trap points. (Just pre-empting the usual argument yet again. )

 

Martin.

There shouldn't be any argument. In mechanical terms they are more-or-less the same thing so P.Way staff treat them as such. From an operating viewpoint, they perform two distinct functions, clearly defined by the use of two different terms. 

 

Thus, a trap point is provided to stop a movement proceeding incorrectly in the right direction - it is there to protect running lines from vehicles exiting sidings or loops without authority (i.e. the result of a SPAD). A side benefit is that it prevents the main point being run through. They are usually of the two tongue pattern and on some lines a full point with a short stub and sand drag and/or stop block was preferred. 

 

Catch points are (or were) provided to derail vehicles running away in the wrong direction, i.e. backwards, down gradients or out of the "inward" end of a loop generally as a result of a goods train becoming divided. Older ones were often single tongue but very few of any kind remain nowadays because the need generally disappeared along with unfitted wagons.

 

Hypothetically, you could have a bi-directional loop on a bi-directional line with trap points at either end, each of which would alternately become catch points depending on the direction of movement.

 

All the diodes down my left side are now throbbing and I'm going to put the kettle on.

 

John  

[The Stationmaster]

Thanks for all the replies, its all useful information.

 

The following pictures show that even with a 2 blade/tongue catch point, there's no guarantee that errant vesicles will come to rest fully clear of the running line.

 

[/url]150261 and 66063 Lostwithiel by Andy Hoare, on Flickr">http://150261 and 66063 Lostwithiel by

[/url]150261 and 66063 Lostwithiel by Andy Hoare, on Flickr">Andy Hoare, on Flickr

 

[/url]">http://

 

[/url]">http://

The usual test was that if you could stand against the bit of the derailed vehicle which was most foul of the adjacent line with your shoulders square on to the adjacent line and if your shoulders were clear of the nearest running rail then you had room to run past it on straight track - very carefully.  I reckon there's probably just about enough room to squeeze past in that example but it would be tight.   Mind you nowadays staff wouldn't be allowed to work anywhere near the derailment in those circumstances and you'd have to block the adjacent line anyway in order to jack up the derailed wagons.

[LNERGE]

My favourite trapping arrangement complete with facing point lock..

 

https://www.flickr.com/photos/jerry-spillett/18316176042/

[russ p]

My favourite trapping arrangement complete with facing point lock..

 

https://www.flickr.com/photos/jerry-spillett/18316176042/

I've never seen that before Richard, excellent. Work the exact opposite of what Jarvis inadvertently created at Potter's Bar

[LNERGE]

I've never seen that before Richard, excellent. Work the exact opposite of what Jarvis inadvertently created at Potter's Bar

Ouch.

[bubbles2]

The usual test was that if you could stand against the bit of the derailed vehicle which was most foul of the adjacent line with your shoulders square on to the adjacent line and if your shoulders were clear of the nearest running rail then you had room to run past it on straight track - very carefully.  I reckon there's probably just about enough room to squeeze past in that example but it would be tight.   Mind you nowadays staff wouldn't be allowed to work anywhere near the derailment in those circumstances and you'd have to block the adjacent line anyway in order to jack up the derailed wagons.

 

In this case passenger trains with drop light windows were not allowed to pass on the down main but hopper windowed units could just get past.

 

[/url]">http://

 

By the way 57305 was on the rather late running down beds.

 

[/url]">http://

[martin_wynne]

My favourite trap points, at Castle Cary:


linked from http://i62.photobucket.com/albums/h119/pugsley_d449/

It isn't a simple set of catch points providing the trap function. It's a full turnout with an over-the-top crossing -- the single wing rail is ramped up to carry the wheel over the running rail. The opposite stock rail stops short. The effect is to dump the offending vehicle into the dirt away from the running line.

It would be a brave passenger to stand on the footbridge while shunting was taking place.

Judging by the condition of the footbridge, the trap has never been used in anger -- hopefully like the vast majority of traps across the network.

Here's another view of that. Notice that the check rail is similarly ramped up, and extends beyond the end of the running rail -- not something seen often. See also that someone has been doing some timber shoving in the foreground -- the timber is skewed out of square:

 

From Wikimedia Creative Commons -- more pics:

 https://commons.wikimedia.org/wiki/Category:Catch_and_trap_points

• CC BY-SA 4.0
  File:Castle Cary catch points - 02.jpg
  Uploaded by Thryduulf
  Created: 6 September 2006

regards,

Martin.

 

[Mike Storey]

Much discussion took place on a previous thread http://www.rmweb.co.uk/community/index.php?/topic/46962-which-direction-should-catch-points-go/

 

It is clear that there are several definitions of the difference between trap and catch, and that exceptions and mis-naming can be found for every one!

 

The very first morning I went live, as a Traffic Manager, I was called out to a derailment at Sheerness. There used to be a bi-directional centre road there (reversing really) with a catch or trap point, take your pick, protecting the two passenger lines into platforms. The middle road was used to reverse freights back into Sheerness Steel. The point consisted of two blades which, if open, would derail a runaway but keep it as centred as possible. (It was not a derailer, which we used in depots). A trip working had moved before the signal had cleared and the trap/catch closed, leaving the last vehicle (first in the direction of movement) hanging over at a perilous angle. We had to edge a 4 CEP past the offending wagon, as slowly as possible to check it would be clear, to allow a hundred or so passengers, who had by then been waiting nearly two hours, to leave the delights of Sheerness-on-Sea. The shoulder to running rail measurement proved very useful then, but you would not find that in any book!

[JDW]

The "Way Out ---> " sign in post #18 seems rather appropriate!

[Il Grifone]

Mike,

 

surely normal GWR practice was to look at whatever other railways were doing and then do the opposite.

 

I thought it was the other way round; the GWR did it the right way first and the others then did it the opposite way (see below).  

[Mark Saunders]

My favourite trapping arrangement complete with facing point lock..

 

https://www.flickr.com/photos/jerry-spillett/18316176042/

 

It was not an unusual arrangement not to have trailing point locks, there was a set at Bedlington North that were only fitted with such in the mid 1980's!

There was a listing in the sectional appendix listing of a small number of such!

 

Mark Saunders

[Grovenor]

 

It was not an unusual arrangement not to have trailing point locks

Which is why they are called facing point locks!

Regards

[keefer]

Quite by chance, I found a YouTube clip showing a trap point doing its job

 

http://youtu.be/Yr5EztEPJS8

 

A bit of background info/comment:

http://www.rail.co.uk/rail-news/2013/steam-locomotive-totally-derailed-at-the-great-central-railway/

 

(NB - I don't want this to degenerate into argument about the whys and wherefores, just thought it's not often something like this is caught on camera)