Description
The Class 313 fleet was developed following extensive trials with the prototype Class 445 "PEP" unit built in the early 1970s. The 313 is similar to its sister classes of Class 314 (Glasgow), Class 315 (Anglia suburban — east London), Class 507 (Merseyside) and Class 508 (Merseyside, formerly Southern Region).
Since they were originally designed for use on Great Northern Suburban Inner Suburban services from Moorgate to Welwyn Garden City or Hertford North, which included a section of 'tube' line built to take standard size trains between Drayton Park and Moorgate, they are built to a slightly smaller loading gauge than conventional trains. They are standard length and width, but the roof is somewhat lower, most noticeable due to the lack of a distinctive "well" for the Stone Faiveley AMBR pantograph on the centre coach. Also, they have to comply with regulations for underground trains, such as having doors at each end of the train for evacuation onto the tracks, and when on 750 V DC supply, the traction supply for each motor coach is separate, whereas on conventional 750 V DC trains each coach in a unit is linked by a 750 V bus line. Due to this, each motor coach has shoe gear on both bogies, whereas normally it would only be provided on the leading bogie. They are also fitted with trip-cocks which are struck by a raised train-stop arm at red signals and will apply the brakes if the train passes one.
The three-car units were originally numbered in the range 313001-064. Each unit is formed of two outer driving motors, and an intermediate trailer equipped with a pantograph. This is a reversal of the practice started in the 1960s where the motors and if applicable pantograph would be carried on an intermediate vehicle, with the outer vehicles being un-powered driving trailers. Part of the reason was to simplify the equipment to allow dual voltage operation, and to keep down weight by spreading heavy equipment (the transformer and motors) between vehicles. The intermediate trailer carries the pantograph and also a transformer and rectifier, which when on 25 kV AC supply provides a 750 V DC supply to the motor coaches, each of which is equipped with four 110 horsepower (82 kW) GEC G310AZ traction motors, two per bogie. When on 750 V DC supply, each motor coach draws its supply directly through its shoe gear.
The Class 313s are fitted with Series Wound DC GEC G310AZ traction motors, which are controlled by a camshaft controlled resistance system, with series and parallel motor groupings and weak field steps. Originally the heating in the motor coaches was provided by passing air over the hot traction and braking resistors, in addition to conventional heaters, though this feature is no longer in use and the pneumatic dampers have been disabled. First Capital Connect and Southern units are now retro-fitted with cab air conditioning equipment.
Class 313s are fitted with rheostatic braking (disabled on London Overground) in addition to conventional 3 step air-operated disc braking; during braking if wheelslide is detected by the WSP (WheelSlide Protection) rheostatic braking is disabled and the disc-braking comes into effect. Additionally units operated by First Capital Connect are equipped with sanding equipment. Unlike some other classes of DMU/EMU additional brake force is not available when the an emergency brake application is initiated and is the equivalent force of a step 3/full service application, however WSP is disabled when making an emergency application.
In addition to the primary suspension (formed of rubber chevron spring and oil dampers), secondary suspension is provided by air 2 air bellows per bogie, the air flow into each bellow is controlled independently by a levelling valve and arm assembly which will allow the suspension to inflate/deflate when the weight of the coach is increased or decreased by passenger loading. The air suspension system is also linked to the braking system via a Variable Load Valve (VLV), this will give an increase in air brake pressure when the coach is more heavily loaded to compensate for the additional weight.
The DMS A coach is equipped with a compressor and main reservoir tank, which provide air to the whole unit via the main reservoir pipe for friction braking, power doors, secondary suspension and pantograph operation.
The DMS B coach is equipped with an MA set (Motor Alternator) which runs on 750 V DC from the AC/DC changeover switch whereby the transformer and rectifier provide the supply when on 25 kV working and by the shoegear directly when on 3rd rail working. The MA provides power for the following equipment:
- 415 V (AC) - Headlight (DC lamp supplied through an additional transformer), traction/braking resistor cooling fan, coach heater fans (the heaters themselves run on 750 V DC).
- 240 V (AC) - Cab heater fan, cab fresh air fan, thermostat fans, appliance sockets.
- 110 V (DC) - Control supply, battery charging, train lighting, cab air conditioning, CCTV system.
Individual vehicles are numbered as follows.
- 62529-62592 - DMSO
- 71213-71276 - PTSO
- 62593-62656 - BDMSO
All units have standard class seating only.
As built, the sliding doors of these units were individually opened by the passengers. Once the driver had stopped the train and the guard had activated the master door release, a passenger could move the door handle gently sideways which would operate a switch controlling the individual door opening circuit. Unfortunately many people did not wait for the guard's release, and gave the handle a much harder tug, which could open the door even if the train had not stopped. Concerns over passenger safety led to the removal of the handles from March 1977. In recent years, push-buttons have been fitted which serve the same purpose as was intended for the handles.
Modifications led to a certain amount of renumbering and reclassification. All 64 units were originally provided with shoebeams on the inner bogie of each motor coach, which was sufficient for their original third-rail duties between Drayton Park and Moorgate. Some units became surplus, and four were transferred to the Colchester-Clacton/Walton route, which has no DC sections; these four units had the shoegear removed, and were renumbered from 313061-4 to 313096-9; this happening in 1987. However, following an accident involving one of these units at Walton on the Naze in August 1987, they were subsequently replaced by Class 310s in 1988. 313s had also worked on the Colchester-Walton/Clacton route between 1981 and 1983. 16 others had shoegear fitted to the outer bogies in addition, and were transferred to the Euston-Watford route where there are long gaps in the conductor rails; these, 313001-016, were not renumbered, but were classified 313/1, the unmodified units becoming 313/0 - prior to this the entire class were simply designated class 313, without subdivisions.
Read more about this topic: British Rail Class 313
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