From the archive: First batch of class “508” electric multiple-units in service

First of the Southern's four-car class "508" units
The Railway Magazine Archive: March 1980

Apart from the underground trains on the Waterloo and City line, the Southern Region of British Railways has, until now, exclusively used hinged doors on its suburban trains; with the advent of 43 four-car sets of class “508” electric multiple units to the South Western Division from the end of last year; however, the long reign of the “slam door” on SR suburban trains has ended.

The new units have been built by British Rail Engineering Limited at York Works at a cost of £26m for the 43 four-car sets, and are the fourth production consignment based on the “PEP” class “445” prototypes built in 1971/2, previous batches being class “313” three-car sets on Great Northern inner-suburban services, class “314” Glasgow “Clyderail” suburban sets and class “507” three-car sets for “Merseyrail” services.

Each unit of a “508” set is made up of four vehicles: two driving motor open seconds (DMOS), each 19,800 mm. (64 ft. I If in.) long over body and with driving cab and all four axles motored; and two trailer open seconds (TOS) 19,920 mm (65 ft. 4¾ in.) long and with no motors. One DMOS and one TOS (type “A”) each have an air compressor, while the second DMOS (type “B”) is equipped with a motor alternator and battery.

On each car side are two air-operated double-leaf sliding doors, the openings being located away from the highly-stressed area over the bogies; a single sliding door is provided on each side at the cab end of the DMOS for use by the guard.

Each double door opening is 1,288 mm. (4 ft. 2¾ in.) wide, but there is no “stand back” facility between the edge of the door opening and the bulkheads, as has been found necessary on London Transport trains to obviate station delays caused by standing passengers blocking the door openings. Racks for light luggage are fitted above the windows and these incorporate handrails for standing passengers.

Mechanism for the electro-pneumatically operated doors is behind hinged covers above each opening. In each DMOS, door control panels are provided adjacent to the single-leaf door at the cab end, energised by a key switch in the cab.

The system allows the doors to be released electrically by the guard and actual door opening is initiated by the passengers on the platform or inside the train using push buttons located at each side of every double-leaf door opening. The external buttons are for opening only; those inside the car can be used to open or close the door.

The guard can close any door left open after passengers have got on and off the train, the doors are then held closed under power and the local push buttons will not open them until the guard presses his “release” button. A lamp on the door control panel shows when all the doors are closed.

The guard’s single-leaf door can be operated independently when the door control panel adjacent to it is energised by the key switch in the cab. A two-way cock on the outside of each car allows one pair of doors on each side of the TOS, or the single doors on each side of the DMOS, to be opened in an emergency.

Each DMOS seats 74 second-class passengers and each TOS 86, so the total seating capacity of a four-car set is 320. Seats, mainly arranged 3+2 across the car with a wide centre gangway, have backs 530 mm. (1 ft. 8¾ in.) high and are made up of individual style shells of glass reinforced plastic mouldings, the upholstery cushions having removable covers for easy cleaning.

Toughened linoleum floor covering is used in the saloon areas and synthetic rubber bonded cork in the doorways. Open fluorescent tubes are used for lighting and ven­tilation slots are positioned beneath the roof ventilators. Access between coaches is provided throughout each four-car set.

An underframe-mounted heater unit incorporating electric heating elements and an electrically-driven fan is provided on all vehicles. Two ducts are built into the saloon floor; one to supply warm air to the saloon through grilles in the seat supports and the other for recirculating air back to the heater through similar grilles at the other side of the coach.

A thermostat operating at 28 and 21 deg. C (83 and 70 deg. F) is fitted in one of the seat supports connected to the recirculating duct. At temperatures above 28 deg. C the fan is operational to provide some air movement in the saloon. Opening hopper ventilators are provided above each window. Each four-car set has one car for smokers, the other three for non-smokers.

The” 508″ class trains have an acceleration rate of O· 72 metres (2-36 ft.) per sec., balancing speed of 106 km. per hour (66 m.p.h.) and a maximum permissible speed of 120 km. per hour (75 m.p.h.). Bogies are of the “BP8” type used on the “PEP” (class “445”) prototypes, with chevron rubber primary springs and a secondary airbag suspension system.

Air-operated disc brakes are fitted throughout. Normal braking of the train is by the dynamic brake. The traction motors are reconnected as generators and braking energy is dissipated as waste heat in the resistor grids.

Braking effort is maintained by controlling the value of the load resistor, using the camshaft equipment. Below 19 km. per hour (12 m.p.h.), the air brakes automatically take over the full braking effort to bring the train to a stand.

On each vehicle, a speed signal derived from each axle is compared with an average of four-axle signals, the speed of adjacent axles and a reference deceleration rate. When wheelslide is detected during dynamic braking on the DMOS vehicles, the affected vehicles will automatically change over to air brake application.

If wheelslide persists on the motor coaches, or occurs on the trailers, the affected axles will have the air brakes on that bogie released and re­applied at a controlled rate intended to prevent the wheelsets from locking. If wheelslip is detected when the train is under power, the motor coach affected will have its power supply interrupted, to be re-established when wheelslip has ceased.

Saloon interior of a class "508" unit
Saloon interior of a class “508” unit, showing un­shielded fluorescent lights and door control push­buttons
Photo: British Railways Board

Spring-operated parking brakes designed to hold the train on a 1 in 32 gradient are mounted on the back of the air-brake cylinder of each DMOS. Operation is by push button from the cab and if this is not released before the unit is moved, an audible warning sounds in the cab when power is applied.

Traction power at 750 V d.c. is taken via the collector shoes from the ground-level conductor rail supply. The control system follows the standard d.c. electric multiple-unit practice by controlled notching of a force-ventilated resistor grid using air/oil cam­shaft equipment. Electro-pneumatic contactors are used for the line breakers and series-parallel grouping of the motors. Three steps of field-weakening are in­troduced by the camshaft.

Auxiliary supplies of 240 V single-phase and 415 V three-phase, both at 50 Hz, come from the motor alternator under each type “B” DMOS vehicle, which is supplied at line voltage (750 V d.c.) from the collector shoes.

The two rows of 40 W fluorescent tube lighting inside the coaches are fed from the 240 V supply via ballast units, with emergency lighting fed through individual inverters from the 110 V battery supply. Each train set has cab-to-cab communication and a public address system connected to loudspeakers in the ceiling of each vehicle.

The outer end of each DMOS is fitted with an automatic “Tightlock” coupler, incorporating electrical and air connections; couplings between DMOS and TOS vehicles are of the BR standard bar pattern with jumper connections for the electric and air lines.

Initially, the 43 four-car sets are being phased into use, as they become available -roughly one set a week. Usually two four-car units are coupled together to form an eight-car train. They are being used on the lines linking Waterloo with Chessington, Shepperton and Hampton Court and, within a few months, will be extended to cover Teddington and some Effingham services.

Further supplies of these new inner-suburban e.m.us are programmed to arrive on the Southern Region each year from the end of 1981 – the expenditure of £58m on 358 of these vehicles has already been authorised.


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