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Aberdeen's experiment is to test the merits of the equal wheel bogie type with central entrances against the single truck type with front and rear entrances, the former capable of seating 72-76 passengers and the latter 62-64 passengers. Both types of car endeavour with considerable success to ensure the maximum comfort and convenience of the passengers. For instance, both saloons are fitted with heating apparatus and a loudspeaker announcement equipment, the value of which will be doubly felt during the black-out periods.
The doors in either case are manually operated twin folding type opening inwards against the loading platforms. In the case of the central entrance type it has been found that the low loading platform and twin staircases allows for quicker loading and off-loading, the task of the conductor is made easier and apparently the platform accident rate is reduced. The seats, supplied by G. D. Peters & Co Ltd., are all of the double transverse type and all have reversible backs and tilting mechanism, with the exception of those behind each staircase partition in the lower saloons and the seats at the front and rear of the staircase in the upper saloons in the bogie type, and with the exception of the four longitudinals in the single truck type.
Apart from the main traction motors, the electrical equipment in both types is identical, and even the motors only vary in dimensions and horse power. The bogie car is fitted with four motors connected in pairs permanently in series; the single truck type has two motors, an arrangement which enables the control equipment to be used on either type of car. In both cases the last controller notch provides for future weakening by the insertion of a suitable shunt resistance. This enables a high free running speed to be maintained; at the same time it does not affect the low speed of the rheostats nor the acceleration of the car. The four motors in the bogie type are each of 34 H.P. and the two motors in the single truck are each of 57 H.P.
Of these it is almost sufficient to say that they are supplied by the E.M.B. Co. Ltd of West Bromwich! However, they are of equal wheel type, and the hornways have been entirely eliminated, the main springing being carried on the axlebox, thus reducing the unsprung weight to a minimum. The long, laminated, semi-elliptic springs are bolted direct to the axlebox which is fitted with a double row of spherical roller bearings. Thus smooth riding is assured; the patented construction enables the axles, when entering a curve, to ease off endways to damp out shocks.
The car body is carried on the centre of the truck bolster, large rubber shock absorbers transferring the weight. A special adjustment controls the height of the shock absorbers. Each end of the bolster is fitted with side bearing blocks of free rubber to keep the body steady, and any tendency of the car body to move too freely when running on sleeper track can be checked by adjusting the central rubber blocks so that the correct amount of weight is carried by those side bearing blocks which also completely insulate the floor of the car from the noise of the truck.
The truck is designed in such a way that the reactions of braking are absorbed, thus preventing distortion of truck members. Unnecessary wear of the wheel flanges is relieved and inertia of the rotating mass is reduced to a minimum by hanging the motors inside the axles as near as possible to the pivotal centre of the bogies. The motors can be lowered without interfering with the body of the car in any way.
Two air wheel brake cylinders are carried on the central bolster of each truck. The air track brakes are actuated by two air cylinders per truck mounted directly over the magnets, thus down pressure is direct and accomplished entirely without levers or bell cranks. The car is actually on an air cushion when the brakes are in action. For emergency, track brake shoes are fitted, with powerful electro-magnets which can be energised by the rheostat current.
The well known E.M.B. patent interlocking control system is fitted to air wheel, air track and magnetic brakes which gives maximum braking without wheel skid. The air wheel brakes used for service stops under dry rail conditions are operated by a separate lever; for wet or greasy rails the track brake is used. Both brakes can be used together in any proportion. In an emergency the main controller handle is switched past the 'off' position to the braking side, thus applying air pressure to the track brake shoes. Further movement of the controller handle brings on the rheostatic brake which energises the track brake magnets. The rheostatic brake is essentially a wheel brake effective only when wheels are turning. The E.M.B. system ensures that when rheostatic notches are reached the air wheel brake is automatically released, preventing both brakes being used together.
Maintenance problems of both truck and brakes have been dealt with very thoroughly. Lubricators have been fitted to all important pins and have been arranged in the most convenient position for routine attention. All brake pins and levers are fitted with hardened bushes. Spray lubricators are provided to lubricate the air cylinders, and the exhaust is taken through quick release valves to the inside of the bolster which is arranged as a silencer. The chamber into which this exhaust is emptied becomes highly charged with oil vapour and it is therefore arranged that the low-pressure side of the cylinders breathe into this same cavity, thus preventing the cylinder walls becoming dry in good weather or rusty in wet weather.
The wheel brake cylinder can be easily dismantled for attention without seriously disturbing the brake gear. The track brake cylinders can be lowered out of position after removing one magnet stop and sliding out the magnet unit. Extra large wheel brake pull-off springs are fitted to reduce adjustments to a minimum. Copper piping for the air system is used throughout.
To obviate radio interference there is one Dubilier condenser per car. One side of the condenser is connected to the negative side of the choke coil, the other side being connected to earth. The choke coil effectively prevents any high-frequency disturbance set up by the motors and control equipment being fed back into the overhead line, whilst the condenser unit by-passes them to earth. The condenser and its protecting fuse are assembled in a sheet-metal case fitted with a watertight lid, the condenser being embedded in high melting point compound. The complete unit is mounted under one of the staircases.
The experiment was successful, and a further 20 bogie cars were ordered in 1949 from English Electric. These were built under sub-contract by R. Y. Pickering of Wishaw because Preston had ceased to build tramcars by this time. They were to the design of the prototypes, with detailed improvements resulting from experience in traffic. The most obvious change was that the lower saloon was painted externally in green with white trim, the prototype being white with green trim.
The underframe, including a well for the centre entrance, was of welded rolled steel sections and extremely rigid. The body was of oak, reinforced with steel angles round the entrances and for strength and rigidity where necessary. The external body panelling was steel plate and the window mullions were clad with aluminium sheeting. The livery was green and cream with the fleet numbers in chrome-plated numerals on each dash. The entrance platform was only 1ft 4in from rail level and 4ft 6in wide. It was covered with studded rubber matting, and a further step took one into the lower saloon. Straight staircases, one on each side, led from the platform to the upper saloon, with the last two steps turning to give direct access to the upper saloon gangway. Quick acting jack-knife doors were fitted on either side of the platforms. The driver had a separate cabin at each end stepped down from the lower saloon floor level. It could be entered from the street or through a bulkhead door from the saloon. The driver had a portable stool, and the cars were equipped with loudspeakers so enabling the driver to announce the stops as in modern continental practice.
The electrical equipment was by English Electric. The four motors were of 38hp each, and there was an impressive array of braking systems including the Maley & Taunton hand brake and EMB pattern air wheel brake. The dominant colour of the interior was green, with different shades used to pick out the pattern on the background material on the ceiling and interior panels. The transverse reversible seats supplied by G. D. Peters were of Dunlopillo and upholstered in green hide. In 1952 the seating was converted to longitudinal to improve passenger flow in the lower saloon and to ease the work of the conductor. Lights were concealed in fittings running the whole length of each saloon and tubular heaters were also provided, eight in the upper saloon and four in the lower. The light and airy nature of the upper saloon was further enhanced by glass eaves in the curves of the roof panels along each side.
The new cars were expensive to operate because of their more complicated electrical equipment; they were also expensive on labour and required two conductors, one for the lower saloon who also operated the single folding doors manually, and one for the upper. To overcome this, mechanically-operated folding double doors were later fitted, worked remotely by the driver. The fitments included an illuminated caution sign and an emergency valve by the doorway. The permitted number of standing passengers was reduced from 20 to five (presumably to prevent interference with the door mechanism or with the conductors' freedom of movement), so reducing the overload capacity from 96 to 79 and hence their revenue-earning potential. The riding quality of these cars was superb and the rapid acceleration hardly noticeable; they were quiet running and comfortable. Perhaps their only shortcoming was the restricted width of the front upper saloon seats and lack of leg room which resulted from the tapering nature of the bodywork.
Aberdeen Corporation Tramways Nos 19-38
Built: R & Y Pickering, Wishaw
Length overall: 38ft Oins
Length of platform: 4ft 6in
Width overall:& 7ft 1.75in
Height to trolley plank: 15ft 2.5 in
Height inside lower saloon: 6ft 0.25in
Height inside upper saloon: 5ft 11.75in
Stairs: Straight
Seats (lower saloon): 32 TU; 2+2 later 30 LU
Seats (upper saloon): 44 TU 2+2
Trucks: EMB lightweight; 5ft wheelbase; 27in diameter wheels
Motors: 4 x EE 327; 38hp
Controllers: EE Z type DB 1
Brakes: Hand wheel, air-wheel, rheostatic and magnetic emergency
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©Andy Taylor. Last updated 28 Nov 2000.