The Push Pull system allows a locomotive to be driven remotely.
The driver of a train has to be at the front so as they can see where they are going. This usually means the locomotive has to be run around the train when the train has to change direction. If the locomotive can be remotely controlled from a cab at the other end of the train, you can avoid doing this.
It is not a new idea at all and several systems have been used for steam, diesel and electric locomotives for over a century. It has gradually come into greater use with modern diesel and electric railway traction. The electric Class 91 used on the East Coast Main Line are all push pull trains. The locomotive is always at the Scotland end of the train and the London end is a Driving Compartment and Luggage Van.
History on the FR
The first experiment with push pull operation was the Gelliwiog Shuttle, that used locomotive Moel Hebog and Carriage 110 in 1975-7. This allowed a train to be driven on from Dduallt up around the spiral to Gelliwiog, which is just short of the new Moelwyn Tunnel on the then incomplete Deviation. This system was based on pneumatics, and required a second man on the locomotive to change gear, as only the throttle and brakes could be remotely controlled. This operation ceased in 1977 when the main service was extended to Llyn Ystradau. The unit was later used for occasional off-peak and Gala shuttles but the carriage when fully fitted out was used in ordinary service. It was temporarily fitted with electronic controls to work with Conway Castle for test purposes in 1988, but by 1989 the driving controls were removed, though it retained through wiring for the later system.
The Push Pull Scheme
In 1986 a proposal was announced  for a three-coach push-pull train with the diesel Conway Castle and refurbished steel carriages with toilet, heating, refreshments and public address for use on winter trains and as a 'Talking Train' with commentary. The loco was fitted with an electro-pneumatic system which allowed control of the throttle and gearbox through electrical connections and was the first true push pull as a second man was not required on the locomotive. The driver had full control from the driving trailer except for starting the engine or reversing. The inclusion of a vigilance device in the locomotive and driving cab meant that the train could be operated with a single driver. Cars 117 and 121 were converted and a new driving trailer observation car Carriage 111 was built. The loco was tested with Carriage 110 in early 1988 but Carriage 111 was not ready until 1990 due to a very heavy workload in Boston Lodge. The whole train received a new green and white livery.
Involvement with the INCA Programme
The Push-Pull scheme was started well before the INCA programme, but the three carriages (112-4) built under that programme were turned out with control wiring, heating and the Push-Pull livery so they could make up the Push Pull train to six cars.
The control system of Criccieth Castle was designed from the outset with push pull working in mind and a full "Pull-By-Wire" system allows complete control and monitoring of the locomotive from the driving console in Carriage 111.
Brakes and electrical connections
Whilst the function of the locomotive is controlled by the electrical signals, the brakes of the train are vacuum operated. To allow proper control of the brakes, the driving cab needs a vacuum supply to allow the brakes to be released. This requires the provision of a second vacuum pipe along the train between the locomotive and driving compartment, and is referred to as the High Vacuum supply. Vacuum reservoirs on this supply are fitted to each carriage to improve the responsiveness of the operation of the brakes from the driving compartment. See the external link below for a description of the operation of the dual pipe vacuum brakes.
All of the carriages built as part of the INCA Programme were fitted with the high vacuum and electrical connections, allowing the full six carriages of the then C set to be used as a push pull train.
Carriage 122 was constructed with a high vacuum pipe (but no high vacuum reservoirs) and electrical connections for use in the push pull train.
In addition to winter trains the Push Pull set was often used on early morning and late evening trains. However in more recent times policy has shifted towards longer trains and the use of steam on all scheduled services where possible. Push-pull working has not been used in recent years and the carriages have been repainted in standard livery.
Over time the carriages have lost their high vacuum reservoirs when they were fitted with diesel fired hot air heating.
Some of the carriages have been withdrawn and Carriage 111, with its driving console, has been reassigned to departmental use (see table below).
The following carriages have been fitted with the high vacuum connections and wiring for push pull operation:
|Key:||In service||Scrapped||Renumbered or repurposed||Preserved elsewhere|
|110||Driving console (removed 1988-99) / 3rd Saloon||In service|
|111||Driving console / 1st Observation (removed 2016)||In service - Departmental use|
|112||3rd Saloon||In service|
|113||3rd Saloon/Guard||In service|
|114||3rd Saloon/Buffet||In service|
|117 (1977)||3rd Saloon||Withdrawn and sold to the Moseley Railway Trust|
|121 (1981)||3rd Saloon||Withdrawn and scrapped 2005|
|122||3rd Saloon||In service|