SVR S&T Dept.
SIGNALLING NOTES - Chris. Hall
The last article covered a lot of ground and I can now report that the rewiring of Bridgnorth box was completed ahead of schedule and was handed back on 27 January 2024. The ground frame at Foley Park was commissioned on 29 February 2024. This controls access to the new siding: at present this is unlocked by a Possession Key that can only be released when Bewdley South and Kidderminster Signal Boxes are closed for normal operation. This was a solution thast was simple to implement and didn’t require any modification to the already existing method of controlling the single line working.
Future operations however envisage the need to access Foley Park siding while both Signal Boxes are open for normal services and this will require more significant changes to the Single Line signalling controls and interlocking. Design work for this is now underway. Part of the scheme requires an additional lineside cabinet adjacent to the Ground Frame to house a key release instrument and associated indications and telephone for the Ground Frame Operator. We have recently started refurbishing an existing cabinet from stock for installation as part of the preparatory works. Another element of the scheme is the replacement of the electrical detection box which proves that the points controlled by the ground frame are set and locked correctly. The detector originally installed at the same time as the points has suffered from the visit of a P.Way tamping machine! A replacement has now been sourced assisted by an exchange of equipment with the Reedham Junction Signal Box group at the North Norfolk railway.
Troughing will need to be laid between the motor points and the section signal to accommodate a new signalling cable with the extra cores needed to control the key release instrument at the ground frame. The new troughing is very slowly increasing in length and an UTX (under track crossing) at FP itself is being prepared for cables to the new ground frame operators’ location cupboard: this will need access for operational staff (for the release instrument). Troughing will need to be laid at the ground frame for the cabling and telephone. A significant amount of re-wiring is required in Kidderminster box along with six new relays, a new lever 55 and a circuit controller and a comprehensive testing programme will be required.
Meanwhile the routine maintenance and testing continues, for which there is a maintenance schedule. Track circuits, for example, are tested annually by monitoring the track circuit relay while a shunt resistance box is connected between the rails and the resistance slowly adjusted. Allowance has to be made for track conditions and we normally record ‘wet’ or ‘dry’. In wet conditions more current than normal flows from rail to rail through the ballast, making the relay show ‘occupied’ more readily, i.e. with a higher resistance. When testing 27T at Bridgnorth we had to record ‘inundated’! There had been multiple failures in the heavy rain and frost. Insulation has been added on the detector bars, and the existing insulation on the stretcher on 27 trap points renewed. The P-Way have installed new insulated rail joints (IRJs) and the Bridgnorth P-Way have also dug out all the dirty ballast touching both rails, so with our fingers crossed we hope the problem has been cured.
Meanwhile the routine maintenance and testing continues - this is where we do lots of work but nothing appears to change as far as the casual observer is concerned. Northwood Crossing has also been receiving some attention recently. The main power supply and standby batteries, essential in this relatively rural location, have now been renewed with new full Network Rail spec. items thanks to a generous benefactor. An apparent fault with one of the flashing red marker lights for loco drivers proved elusive to locate. As one point it was thought to be the electronic flasher circuit board that was at fault and although this proved not to be the case it has triggered a project to produce a spare unit in case of future failures. Across the railway we had noticed that some standby batteries weren‘t lasting as well as they should and this was found to be as a result of over charging, so all chargers have now been adjusted to optimum levels to prolong battery life. Routine earth tests have shown signs of a cable fault developing between Highley and Bridgnorth. This has now been narrowed down to between Hampton Loade Up Distant and Bridgnorth Down Distant so that Sterns area is the main suspect! This sort of work can take a whole team several days to trace. The use of radios and days when the railway is closed greatly speeds up the process.
Bridgnorth, Kidderminster and both the Bewdley signal boxes have illuminated track layout diagrams that show the signalmen the location of trains under their control. Over recent years the filament lamps in most of these diagrams have been replaced by red LEDs using in-house developed direct replacement plug-in lamp fittings with a 3D printed body. Bewdley South box however has a much older type of diagram which originally graced St Austell signal box. This uses a single white light per track circuit and has been rather more complex to update while retaining the historical appearance of the original. Amongst other complications, commercially available replacements for the filament lamps would be too bright and have the wrong colour so we have developed a small multi-LED circuit board unit. These have been carefully designed to replicate directly the light output of the previous filament lamps and several have now been installed to see how they perform. In all cases the LED replacements are practically indistinguishable from the original from the signalman‘s point of view. For the S&T department however the increased reliability of LEDs means reduced maintenance and call outs whilst the change also overcomes the inevitable increasing difficulty and cost of finding new filament lamps.
Brian has rebuilt the special twin relay which is fitted inside the intermediate token instrument at Arley which works in the long section Bewdley North to Highley. We are just waiting on a closed day with sufficient testers available, under the watchful eye of Tester-in-Charge Fred Cotterell to bring this back into use, allowing full ‘shut in’ facilities once more at AY.
Now we turn our attention to Highley where the aim of the project is to provide a shunt signal at the north end to enable trains to be properly signalled off the single line into the yard. The south end has been provided with a signal for this purpose for many years and, with the agreement of the signalling inspectorate, we have decided to provide the same facility at the north end. This will enhance the safety at Highley as the north end currently relies on a handsignal from the box.
The design would require a new cam block on lever 1 and signal wire run to work the new disc signal. Modern health and safety considerations suggest that points fitted with a facing point lock should lock both routes where this is reasonably practicable. Since the 1950‘s, Western practice when modifications were to be made would be to have a disc signal read both ways rather than be passed at Danger for some moves. The existing arrangement where disc 7 has a yellow face and can be passed at Danger for moves into the headshunt would thus be superseded: FPL 4 would thus lock 5 points both ways and the disc 7 at the north end would have a red face and read both to the headshunt and to the single line. Whether we fit a single disc or a double disc (worked by selection) here is undecided but does not affect the mechanical locking. The points at the north end of Highley now lock both ways (although the interlocking doesn‘t yet permit that) in readiness for the alteration.
I should explain ‘selection’ - this is where two signals are controlled by a single lever and wire run. It is used principally at locations where there are not sufficient spare levers available for each signal to have a separate lever. At the detection a pulley is used to transfer the drive from the lever to two wires, each passing through the detection, the position of the mechanical detection slides determining which signal comes off.
Planning for this work is at an early stage but to achieve this we will need to make some alterations to the mechanical locking. The lever frame at Highley is not of Great Western origin and has levers pitched at 5″ centres. It was converted to GW ‘5-bar’ locking in 1947 by which time lever 1 was a spare (hence no cam box). Although GW 5-bar frames had levers at 4″ spacing, there were many places where GW frames with spacing of 5¼″ and 4″ were converted to ‘5-bar’. Special locking trays at Highley were needed to accommodate the 5″ spacing. We have therefore had to seek an order for some gunmetal bar from which we can machine the ten fixed locks required by the design. This is a shame as we have plenty of spare nibs for 4″ frames.
We have several BR (Western) single disc signals in various states of readiness but these would be out of place at Highley and we are therefore refurbishing a GW single disc signal, which is the appropriate type for this location.
The operating floors of the signal boxes are the visible part of the S&T department‘s responsibilities. Somewhat akin to ice-bergs however, there is a considerable amount of complex equipment hidden away from the sight of everyone other than department members in the locking rooms on the lower floors of the signal boxes and in various lineside cabinets along the line. Even a major job such as the recent rewire of Bridgnorth Signal Box therefore leaves almost no visible trace as demonstrated by the photograph in the last issue of SVR News taken after the completion of the project. On that occasion however some of team decided to commemorate the event by adjusting the equipment, albeit very temporarily, to show the completion date as can be seen by very close scrutiny of the photograph. In fact even the author of the article himself failed to notice the ‘modification’ until it was pointed out to him after April 1st!
One of the aforementioned lineside cabinets at the North end of platform 2 at Bridgnorth is reaching the point of needing significant repairs. It has now been decided to renew the cabinet completely and relocate it in a slightly different position to provide for a future move of the signal at the end of the platform further Northwards. The replacement cabinet has now been assembled and is in the final stages being wired and tested in our workshop at Kidderminster prior to transport to site. The project will also involve the renewal and replacement of some of the cables back to the signal box, along with those to the adjacent signals and track circuit connections. It anticipated that this will take place ready for changeover and commissioning during a non-running period next winter.
Presentation of our beautiful signals remains a high priority, so much use has been made of the MEWP in the last 2 weeks to repaint finial balls (the red fades quickly), change signal arms and scrub off the green algae that clings to the posts. It‘s all cosmetic of course, but the visitors that come here will hopefully notice and appreciate the effort!
In several places across the railway the track has sunk, meaning the rails are now rubbing our rodding and equipment. This adds friction to the lever and in some cases can cause track circuits to fail. We have had to dig and level rollers in places or change rodding joints for deeper sets to counteract this. Matthew Morgan has assisted the Deputy Signalling Manager in strain gauge testing all the levers on the railway and is pleased to report that everything was within specification as ‘acceptable’ even though some pulls, we already knew, are at the heavier end of the range.
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