Signalling & Track

Signalling at Leadhills

The signalling at Leadhills has developed over a number of stages. The points at the north (yard) end of the Down Loop had originally been hand worked. The points at the south (Glengonnar) end required to be fitted with a facing point lock (FPL) because they are on a part of the line used by loaded passenger trains. The FPL originally only locked these points in the ‘normal’ position, i.e. set for the Platform Line. As an interim arrangement, by 1992 the points and FPL were worked from a two-lever ground frame which was released by the train staff. The hand points giving access to the single line from the engine shed and yard area were fitted with an Annett’s lock in 1994. To release the points, the train staff had to be inserted in the lock and turned, then a slide drawn across. The staff could only be removed from the lock once the points and the slide were returned to the normal position.

The re-assembly of the lever frame in the new signal box was completed in 1996. It is a ‘Saxby & Farmer 1888 Duplex’ frame of 17 levers, which are set at 102mm (4″) between centres. Originally it was envisaged that a major locking alteration could be avoided by designing the track and signalling layout at Leadhills along similar lines to that which the frame had formerly worked at Arrochar. The first signalling equipment to be worked from the signal box was based on that assumption.

This work was completed in 1998. Just five levers were in use at that stage and only the interlocking necessary to lock those few levers was fitted. The south loop points were relaid on a new alignment and connected to lever 7 in the signal box. The FPL was connected to lever 13. One of the new signals, number 8, had not existed in the equivalent layout at Arrochar, so a small addition to the locking was needed to interlock it with the points. The two Down direction signals have ex-Caledonian Railway lower quadrant semaphore arms fitted on lattice posts. The Up direction signals have upper quadrant arms on tubular posts. As only one train may occupy the line at a time, there was no need to provide interlocking to prevent opposing signals being cleared against each other. This made it possible to clear the Up and Down direction signals simultaneously and leave the signal box unattended on days when there was insufficient staff on site to man the box.

To improve operational flexibility, two additional signals were brought into use in 2000.

Disc shunting signals 2 and 9 were placed in a temporary position ahead of the points at the north end of the station loop, which remained hand operated at this stage. Following the removal of the Annett’s lock from the yard points, the Annett’s key train staff was replaced with a simple wooden staff, a replica of the original staff used on the line during standard gauge times. The clearance of signal 2 or 9 was authority for a train to enter the Down Loop or Platform Line respectively. Trains were now permitted to run from the yard into the station without the train staff. To pass beyond the starting signals, the driver had to be in possession of the train staff, in addition to the signal being cleared. Levers 2, 9, and 10 were brought into use, and the necessary interlocking was fitted. Lever 10 was not connected to any equipment, but it had to be operated by the signalman because the interlocking required that it be in the normal position to clear signal 2, but to clear signal 9 it had to be reverse. The lever was painted green to denote that it had to be “pulled for interlocking purposes”. The reason why these levers were interlocked in this manner was due to the intention that the points at the north end of the loop would be connected to lever 10 at a later date. The disc signals 2 and 9 would then be combined and moved to a position in front of the points.

As the layout at Leadhills evolved and consideration was given as to how it would be used in the future, it became clear that the interlocking would have to be redesigned to correspond with a revised layout of signals. In order to more sensibly group the levers together and seeing as a complete re-lock had to be undertaken, the opportunity was taken to rearrange the levers working all but one of the five signals already in use. The south loop points and the facing point lock continued to be worked by levers 7 and 13 respectively, to avoid having to alter their rodding runs. Luckily these numbers fitted in quite well with the new numbering scheme.

The lever frame was re-locked in 2003 to our own design, the locking work being carried out by members of the Bo’ness and Kinneil Railway.

The facing point lock (number 13) was altered so that it can now lock the south loop points in either position. A new disc shunting signal, number 14, reads over these points in the reverse position. The points at the north end of the loop became worked from the signal box (lever 4). Disc shunting signals were provided to protect the points from every direction. Disc signals 2 and 3 read over the points in the facing direction and in view of the distance from the signal box, mechanical detection of the points was provided.

All opposing signals are locked against each other, except when the ‘king lever’ (lever 12) is reversed. This enables the signal box to continue to be left unattended if desired, while the passenger train runs back and forth. When the king lever is reversed, the south loop points are locked in the normal position and signals 2 and 3 cannot be cleared, to prevent a second train being signalled from the yard towards the station. The wooden train staff is to be replaced by an Annett’s key and an Annett’s lock will be fitted to lever 12 to ensure that it can only be moved while no train is occupying the single line section.

Because the signalman’s view of signals 5 and 6 can be obstructed, electric repeaters were provided in the signal box (brought into use in 2004). The ‘calling-on’ signal (number 15) was also commissioned in 2004. This signal is used to admit a train into the Platform Line when it is already occupied by vehicles, e.g. when the locomotive is running round its train.

When completed, the signalling will be as shown.

Signals 10 and 17 will be erected and commissioned at a later date. These signals will permit rounding of trains to be carried out while the single line is occupied. The OTW section will apply beyond the advanced starting signal, number 10. Lineside telephones will be provided at the outer home signal and at the north end of the loop. These will be connected to a small Strowger exchange. It is envisaged that a second platform will be built alongside the Down Loop, as the signalling has been designed to cater for two train operation.

The Signal Box

Above the lever frame is the signal box diagram showing all the signals and points along with their lever numbers.

The diagram was drawn in the later style used on the former Scottish Region of British Rail, using Computer Aided Design (CAD). In the photograph, all the levers are seen in the ‘normal’ position. When a lever is pulled to the forward position, it is said to be ‘reverse’. Each lever is fitted with a badge stating its number and description, as listed below. The badges also show the ‘pulls’, meaning any other levers which must first be pulled reverse before that lever can be pulled.

1 – (Spare)
2 – Sidings to Platform Line
3 – Sidings to Down Loop (Pull 4)
4 – Sidings and Down Loop
5 – Down Loop to Sidings (Pull 4)
6 – Platform Line to Sidings
7 – Up Facing
8 – Down Loop Starting (Pull 7)
9 – Platform Line Starting
10 – Down Advanced Starting
11 – (Spare)
12 – King Lever (Pull 13)
13 – No.7 Points F.P.L.
14 – Single Line to Down Loop (Pull 7,13)
15 – Up Calling On (Pull 13)
16 – Up Home (Pull 13)
17 – Up Outer Home (Pull 13)

The levers are interlocked with one another so as to enforce correct operation of the frame and guard against human error.

The above shows the arrangement of the mechanical locking which is situated underneath the floor of the signal box. The components shown in blue are the ‘tappets’. The tappets are connected to the levers and move vertically (as viewed on the diagram) when the lever is moved. The pieces coloured green are the ‘locks’, which are held in channels in which they move horizontally. Some of the locks are connected by being rivetted to bars so that they move together in unison. When a lock is driven into a notch in the side of a tappet, it prevents the tappet and hence the lever from being moved (note: as the tappets are ‘second-hand’, a few of them have extra notches that serve no purpose now). The bevelled edges on the notches and locks enable the latter to be pushed out when the lever is moved, provided that it is free to do so. In some cases a bar is not joined to the lock but is fitted with a ‘stud’ that pushes against it. This is indicated on the diagram by a small arrow. A ‘butt’ is also indicated by an arrow. Lever 12 has a second tappet (called a ‘top swinger’) that is attached to the main tappet but is able to slide horizontally. This achieves the ‘conditional locking’ associated with the king lever.