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Point rodding and signalling confusion


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Hi there,
   Im currently looking to build a layout, and aiming to make it as realistic as possible based on the former GWR during the mid-1950s. Because im obviously a bit of a mental nutcase, I intend to run point rodding, signal runs and even install facing point locks. After finally finding the book "Railway Signal engineering (Mechanical)" as part of googles book archival project and reading many parts to further my knowledge, I have begun to understand there is more than i had ever thought happening. However with many things reading this has left me with certain questions, non of which have been helped by reading many articles online. My first relates to facing point locks and more specifically selectors. In regards to point selectors, I understand that this is to lock a signal near the point from being pulled while the point is against it. My question. Is this for every point that the main signal encounters in the block? For example, if the block has a siding coming off it does this also need to be linked to the signal by its selector? The only pictures I can find showing these selectors unfortunately are after they are redundant and simply there by association with the point lock or controlling a ground signal and the second selector laying dormant. Further to my previous question, if a point is at a junction with multiple signals, are addition selectors added to a point to lock additional signals?

My second question is about double slips and there facing point locks. The book mentioned prior shows a diagram of a movable crossing which I am assuming would remain very similar to the setup needed for a double slip adding an additional pair of detectors and splitting the control rod to pull both blades separately instead of in unison? As well as adding additional selector/s. For a little context ive added the diagram below.

 

image.png.c1773ae67497ef5330affc6475836235.png

 

 

 

Hoping you can help. Thanks in advance.


Jonathan
 

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I have no idea what a "selector" is but:

 

Interlocking (which is to be found within the signal box on mechanical frames) is to stop the signalman doing something he shouldn't.

 

Detection (mechanical or electrical) is to show that something has happened after a signalman has done something and is to be found out on the railway at a place where the movement of a piece of equipment is to be detected.

 

Both interface with the signals and points to prevent situations which are adverse to the proper running of the railway.

 

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Forgive the poor watermarked image linked here but the apparatus in the foreground of the image is the selector (I didn't know this until i read the book mentioned) and its directly connected to the lock of the point. From my research this and the detectors im referring to on the points were both additional fail-safes to coexist with interlocking. The detector mentioned preventing the facing point lock being released by the addition of a bar that would depress with the weight of a piece of rolling stock stopping the signalman releasing the lock.

 

 

railway-signal-mechanical-interlocking-s

Edited by jonathan3005
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Hi there, thankyou for the photos and the name change. I have a feeling they may have changed there official name since 1932 in this case. I knew it was a switch diamond but my question was in my initial post, if the setup from a rodding and locking perspective was similar? As i cant find any photos showing the rodding in any great detail and none of the facing locking on a double slip. :) 

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Double slip operation in most cases drives the 4 blades at each end from one lever and the drive is split to allow each pair to be individually adjusted, but all 4 blades move in the same direction so you don't have the reversing cranks shown on the switch diamond (movable elbows to you if you are modelling GWR) Each pair of blades that needs an FPL will have one,  The detector slides on points can also be used as selectors in cases where one lever will operate either one of two signals depending on the point position, the name depends on the application.

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1 hour ago, micknich2003 said:

Your "Double Slip" drawing is actually a Switch Diamond, see attached.

Bilton Junction K Switches.jpg

This switch diamond is out of use. You can clearly see the fishplates up against the webs of the closed switches bolted to the timbers, and it is easy to make out the point clamp on the near closed switch, once you know to look for it. I can't see a point clamp on the far closed switch, and I wonder whether the is one, since this is the trailing direction. There looks to be a block wedged in the facing open switch.

Edited by Jeremy C
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Thankyou Keith and thankyou also to Mick, Also the more you know Jeremy :) 

 

Halfway though writing a reply and another arrives answering my follow on question. My last question regarding this would be to ask how a double slip goes about handling 3 routes with 3 signals as the selectors only allow 2 signals. My example (Defiantly not lifted from my track plan :D ) calls for a route from blocks 2 - 5, 2 - 3, 1 - 4 and 3 - 4. 

image.png.928ef35a5485543835ef116de0346d53.png

Cheers again

 

Jon

Edited by jonathan3005
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Why a double slip? There are no signals for movements over the crossover.

 

I doubt you have any need for selectors at all. I don't know much about GW practice, but most railways provided a lever for each signal, and I think it highly unlikely that the two signals at bk2 would be operated by the same lever.

 

Each signal would detect its facing point and FPL. If you have a double slip rather than a single slip, then the bk2 to bk3 signal would presumably detect both the facing point and the facing switches/FPL of the slip.

 

If you only have a single slip, then the signal at bk1 would not detect anything; all the interlocking needed would be in the lever frame in the signalbox.

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I picked a double slip as a single wouldn't allow the straight movement from bk1 to bk4 or the route from bk2 to bk3. Forgive my naivety here but there is only a single signal dedicated for movements across the slip. The branch signal at bk2 allowing movements across to bk3. The other routes are straight or are a main route.

 

Hang on so this could be my lack of knowledge but selectors are only used when signals are required to operate together and not as a safety? 

Edited by jonathan3005
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A single slip is a diamond crossing (so both straight movements are possible; in your example these are bk1 to bk4 and bk2 to bk3) plus one chord between the two lines (in your example you would orientate it to allow bk3 to bk4). A double slip has both chords, which in your example would also allow bk1 to bk2 or vice versa, but neither of these routes have signals.

 

Three of the four signals in your plan contol movements through the slip. Only bk2 to bk5 does not use the slip.

19 minutes ago, jonathan3005 said:

Hang on so this could be my lack of knowledge but selectors are only used when signals are required to operate together and not as a safety?

Detectors are used for safety. Selectors combine detectors with some other mechanism. See the bottom diagram in @micknich2003's post, which detects both switches and the FPL, and has a floating wheel so that a single lever operates both signals (but only one at a time) according to how the points are set.

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 Ive finally understood why a single slip would be perfect, why my brain had decided it wasn't viable, your guess is as good as mine. Thankyou for bearing with me. Ill amend my plan to feature a single slip. Do i assume my signalling is now correct?

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Jonathan can you draw a sketch showing exactly what sort of track layout you're aiming to produce in your model please/. If it involves a single slip it is nice and easy as the two switches would be worked by different levers.  Double slips can be a lot more complex because the way the two different ends are worked depends very much on the track layout but it was unusual on the GWR/WR to find both ends worked by the same lever (it wpould be a heavy pull particularly as they normally needed to work on conjunction with other points and indeed you can sometimes find the two switches at the same end worked by different levers - it all depends on what is required operationally and the way the interlocking in the signal box lever frame needs to work.

 

You will find various signal box diagrams on this site although none are GWR -

https://www.s-r-s.org.uk/html/gwa/S2809.htm

 

Taking an example from the GNR section of that site have a look at this diagram to see how point ends oirk in conjunction with each other as crossovers - look how levers 28 & 39 work the two different ends of a double slip to form crossovers wotking in conjunction with other points.  and lever 52 is interesting because it too works a double slip as one end of a crossover but the switches at the other end of the slip are not numbered - because they are operated by hand levers on the ground adjacent to the slip.

http://lymmobservatory.net/railways/sbdiagrams/finsbury_park_no_3.jpg

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13 hours ago, jonathan3005 said:

 Ive finally understood why a single slip would be perfect, why my brain had decided it wasn't viable, your guess is as good as mine. Thankyou for bearing with me. Ill amend my plan to feature a single slip. Do i assume my signalling is now correct?

A single slip would defnitely allow the movements you've listed.  The sketch below replicates the movements you were seeking with the layout you posted above - i.e.  1 - 4.  2 -5  (the two main line routes); and  2 - 3,  3 - 4 (the two branch line routes).  I have only shown the signals immediately relevant to the junction and have added the only two facing point locks which are needed (A1 &. A2).

 

You will see that one end of the single slip works to form a crossover with the facing point  - A.  The other end of the slip (B) is simply worked as a trailing point in the route 1-4, and is reversed to form the route 3-4.  For interlocking and safety reason the facing point locks (FPLs) on A are worked by two separate levers.  In addition because of the routes available they will work slightly differently - FPL A1 will bolt the main line facing point in either position - set normal for the mainline route 2-5, or reversed for the branch line route 2-3.  The other facing point lock A2 will only bolt that end of A in its normal position - for the facing route 3 -4.

 

The two point levers A & B will lock each other, i.e. if either of the levers is reversed the other will be locked in its normal position because it sets a conflicting route when reversed.

 

Signal 21 detects points A standing normal (straight route) and A1 bolted to secure the points,  Signal 23 detects points A reversed (branch line route) and A1 bolted to secure the points in the reverse position.  In the signal box the interlocking will work like this - signal lever 21 reversed will lock point lever A at normal; point lever A reversed will lock signal lever 21 at normal and release signal lever 23 (point lever A reversed will also lock signal levers 1 and 3 (before anyone points out something else I'm keeping it basic) and signal 3 will lock point lever A.  There is no need to detect B because it is a trailing point.

 

Point lever B (in addition to locking point lever A)  will release signal lever 3.  Signal lever 3 reversed will lock Point A.

 

I have kept the interlocking simple to reflect the basic requirements.  GWR locking changed over the years and would at one time have achieved what I have set out above in a different way. For example at one period a lot of the interlocking was via FPL levers which economised on the amount of interlocking required but was eventually recognsed as posing safety risks in the event of FPL levers being disconnected. 

 

I hope this makes things a bit clearer for you.

 

Scan.jpeg.72f4ed5e2a28b84873dcb1228a5defbc.jpeg

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Hi Mike, 

               Ive attached my plan as it stands (The only bit WIP is the fiddleyard). I appoligise for the crude graphics but hope it shows my intended plan. The only change is the siding and its shunt block (only for controlling this movement) and obviously the shunt signal. As you can see after the wisdom of Jeremy last night ive amended it to feature a single slip. Your explanation of the locking is most helpful and your diagram has definitely rid me of most of my confusion. Thankyou for your help and it is definitely much clearer.

image.png.bf9d4cc44e013858f3a59fed927c6b48.png

 

Edited by jonathan3005
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Hi folks, its been a few days and some developments. I bought myself a signal kit, not a very big one i might add. A pair of LMS/BR ground signals from MSE with the intention of automating them. More as a, if i do a job on it i haven't wasted much in the way of funds. Ive begun these however white metal doesn't like my all or nothing soldering iron. So Ive also bought a new soldering iron as a result, although the good folks at Amazon have decided prime means next Tuesday despite it being ordered Tuesday with one day delivery :scratchhead:

 

The main reason for my post today is that I have a question regarding the plan above. My question is if i were to enter bk5 with the intention of entering bk4 remembering this line is unidirectional. Do i need a shunt signal in the reverse direction to facilitate this? 

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Yes, a shunt signal is usually provided for reversing into a siding. Sometimes omitted if the move is infrequent and the signalbox close enough for the Bobby to use a green flag out of the window.

By rights that siding also needs a trap point to protect the mainline.

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  • 2 weeks later...

Just to add to the discussion of a "selector".  The use of a floating wheel attached either by a wire to, or directly on, the lower end of the signal box lever and two wires from the two signals around this wheel, means that when the lever is pulled, both signals are pulled.  But because of the detector attached to the point blades, only one of the signals is free to move.  So pulling both wires only actually clears one signal arm, which is automatically the arm appropriate to the route the points are set for.

 

If you are able to make it to Scotland, this arrangement is easily visible at Aviemore, on the Strathspey Railway, where the new (installed 2019) AV5 signal controlling access to the Strathspey from NR has 2 arms, for the main platform road or the loop, but is operated from just one lever on the ground frame.  As it's a GF, all the workings are visible, rather than hidden in the locking room under a signal box.

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  • 5 weeks later...

Sorry for my absence of this topic. Been working on a different layout although ill keep my mouth closed on that one :) Thankyou for the info David although i may have to postpone the Scottish trip for the time being with everything as it is. The track above is non scenic but also simply to show how the fiddle yard would link in at the ends. The number of tracks should be discounted on the upper portion. Atm im faffing with working ground signals to try and gain a foothold, unfortunately it didn't go well with the base pinging off into the other room never to be seen again and the other falling pray to my first effort with white metal and ending up with a big (comparatively) melt mark. Not the forum spot possibly but any tips on this will be most welcome.

 

Jon

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