151 IR Signalling

Irish Railway Record Society

Irish Rail Signalling - Part Two
Oliver Doyle

ELECTRIC SIGNAL CABINS

There are seven electric signal cabins (not six as quoted in JOURNAL 150), Heuston, Killonan Junction, Limerick Station, Manulla Junction, Ballina, Kilkenny, and Little Island.

Heuston Heuston, a superb example of an early electro-mechanical power signal cabin, was commissioned by the GSR in 1938 to replace three earlier mechanical cabins, Kingsbridge, Island Bridge Junction and Liffey Bridge Junction. It has a 76-lever frame of miniature levers with full size mechanical locking at the back. A unique feature of this frame is the recently installed switches in both the normal and reverse positions of each lever feeding indications of the levers’ positions to a programmable logic controller (PLC). Because of the age of the frame and the time and disruption it would take to overhaul the locking system, it was decided to have a PLC – in effect a simple computer – monitor the lever movements and record then on a printout. The locking tables were programmed into the PLC and in case of the PLC detecting any wrong combination of levers, it generates an alarm highlighting a possible conflicting movement.

Over the years, particularly in the 1970s when the valeting shed was erected and two new platforms provided, additional devices were required to be controlled. As it was impractical to extend the lever frame, the company opted instead to provide panels of control switches over the levers and electrically interlock both. After more than 70 years, this fine example of electro-mechanical engineering is being replaced by a modern computerised system during 2002.

A unique device, a zerograph, is used to work trains between Inchicore and Heuston over the up line which is one direction only – up from Inchicore to Heuston. The device has a dial with xx points and a needle, which rotates to a particular point depending on the destination of the approaching train. The Inchicore signalman depresses his zerograph train describer key a number of times according to a predetermined code and the needles in both cabins indicate the destination of the train. When the train has left the section at Heuston, the Heuston signalman depresses his rest key and the zerographs restore to the home position.

Killonan Junction Killonan Junction is retained as an interface signal cabin between the CTC and the mechanically signalled branch to Ballybrophy as well as operating the adjacent level crossing and monitoring the remote 4-barrier crossing at Lisnagry. The main control panel is a standard CTC local control panel usually only used in the event of failure of the main CTC system but in the case of Killonan it is used while the Nenagh line is open. Killonan then operates as the fringe box to the CTC. When Killonan is switched out the CTC works to Limerick Check as the fringe box.

Killonan has three mechanical levers – all that remains of the original 20-lever Railway Signal Co. frame. Lever 1 acts as the interface between the electric panel and interlocking of the branch-starting signal with the ETS. When a token is obtained for the Birdhill section, it allows the signalperson withdraw the key to release the starting signal. The key is place in the lock on No. 1 lever and the lever pulls thereby releasing the electric lock which allows the starting signal to clear provided the starting signal switch on the panel is set to ‘clear’.

No. 3 lever can only be restored if the level crossing gates are closed against the road and locked. This allows the protecting signals to be cleared for trains to proceed.

Killonan has one of the few examples in Ireland of a single line token ‘drawer’ into which a token can be placed to indicate to an intermediate automatic level crossing that the line is closed. This was supplied by the Railway Signal Co. and is for a ‘C’ pattern staff, which is the Killonan-Birdhill pattern. When the last train before closing arrives at Killonan Junction the token, instead of being placed in the normal ETS instrument, is placed in the ‘drawer’. The token is first inserted into the drawer and then pressed forward into the mechanism to operate the electrical contacts indicating to the automatic half barrier crossing at xxx that the line is ‘closed’. In the event of a person requiring to use the level crossing emergency telephone they will be made aware that the line is closed and they will not receive a response.

When the line is to be re-opened, the token is removed from the ‘drawer’ and placed in the ETS instrument. When a train requires to proceed to Birdhill the signalman obtains a token in the normal way allowing him to withdraw the starting signal key for the interface lever, No. 1. This prevents a signalperson taking the token from the ‘drawer’ and erroneously handing it direct to the driver of a train.

Manulla Junction Here there is a simple layout of a single turnout where the Ballina branch diverges from the Athlone-Westport line, controlled by an electric interlocking with an OCS (one control per switch) panel. The panel only controls the station layout with ETS sections to Westport, Claremorris and Ballina.

The ground frame worked siding at Castlebar, released by the ETS, and is interlocked with the Manulla Junction signalling. The Castlebar turnout faces trains from Westport and the signal which ‘proves’ the points is MJ11 at the Dublin end of Castlebar platform. In case of the turnout being in an incorrect position, MJ11 will not clear. The siding at Castlebar has been little used for some time and is for permanent way use only. It is controlled by a ground frame with an Annett’s lock, the key of which is on the Westport-Manulla Junction ETS. When the ETS key opens the lock it releases the 3 levers. (1 Control lever, 2 Points Lock, 3 Points lever). Trains may lock themselves into the siding and the ETS can be removed from the ground frame and placed in a subsidiary instrument in an adjacent cabinet. This allows a Manulla Junction staff to be obtailed for the Manulla Junction-Westport section from either end.

The ETS ‘starting signal release’ key has a special box into which the key is inserted to release the starting signal. When the key is rotated it makes an electrical contact indicating to the panel that the ETS has been obtained and the relevant starting signal can be cleared from the panel switches.

Kilkenny Unlike Manualla Junction, Kilkenny signal cabin controls both the station area, which includes the Lavistown loop, and the sections to Bagenalstown and Thomastown. It has an OCS panel with additional switches for ‘line closed’, ‘traffic direction’ and ‘pilot working’. The ‘line closed’ switch is operated when the signalman is closing the cabin and indicates to the AHB level crossing at xxx that the line is closed – in effect the equivalent of the mechanical apparatus at Killonan Junction for holding the ETS when the section is closed. The ‘traffic direction’ switches – one each for the Bagenalstown and Thomastown sections - are used to set the direction of the next movement in the up or down direction between Kilkenny and the relevant cabin at the other end of the section. Both signal persons must have their ‘traffic directions’ set for the same direction and no train between the two ‘block posts’ before the signals will clear to allow a train enter the section. The ‘pilot working’ switches, when operated, allow special arrangements to be implemented when a failure of the signalling occurs between two block posts and the section is under the control of a pilotman.

Limerick Station The signal cabin here has an Entrance/Exit (En/Ex) panel where the signalman presses a switch at the entrance to the route he wished to set followed by a switch at the exit from the desired route. However, due to age this panel is no longer used and the signalman now has an additional OCS panel which is used to operate the points and signals. Control between Limerick station and Limerick Check cabins is by ????.

Little island A small but interesting signal cabin. It is basically an electric cabin but has one mechanical lever retained after the removal of the original mechanical frame. The mechanical frame was replaced by a simple electric OCS panel with the sole lever providing an interface between the level crossing and the panel. When the level crossing is locked against the road by the lever it provides an electrical indication that the line is clear and the signals could be cleared by the panel. However, the level crossing has been superceded by an over-bridge and is almost defunct.

The sections to Cork and Cobh (or Glounthaune if switched in) are controlled by Harper’s double line Block Instruments.

Ballina When the station layout here was re-modelled in 1975, the mechanical cabin was demolished and a new electric signal cabin of basic design was constructed and fitted with an OCS panel which remains in use today. The panel controls that station layout but working to Manulla Junction is by ETS and an elecric lock, operated by the starting signal release key from the ETS instrument, is used to indicate to the elecric system that a token has been obtained.

The remainder of this article appears in IRRS Journal number 151, published June 2003.