This article, from Cassier's Magazine, October 1898, describes the Glasgow District Subway, a cable-operated subway.
Although regulated by the Board of Trade as a railway, it is simply an underground system of cable tramways. It is all underground, save at a few of the stations, and it is worked entirely by cables driven from one power station. It is a tubular railway in two circles, the cars running in opposite directions through two separate but parallel tunnels. Thus, two ropes are required, one for each tunnel, on the inner track and outer track, respectively. The whole distance around the circle is 6 1/2 miles, and for each circle about seven miles of wire cable are wound on to the pay-out drums.
The route is within the most populous and most actively employed areas of the city, and in the completion of the circle the river Clyde has to be dived under twice. As a system of street traffic the line traverses at several points three other systems of city and suburban lines of communication, with which it comes more or less into competition, viz., the street tramways system of the Corporation of Glasgow and the circular underground railways of the North British and Caledonian Railway companies. Yet it serves portions of the city not served by either of these systems, and it affords a valuable connecting link between these other systems. While, like Hal o' the Wynd, fighting for its "ain hand," the Glasgow District Subway also acts as a feeder to its competitors.
One distinct advantage of the subway is that it relieves the congestion of the street traffic without rendering the streets unsightly, as an elevated railway does; and another advantage is, that while it conveys passengers under the streets, it does not stifle them with sulphurous fumes, as an underground steam railway does. Still a further advantage is, that by running in separate tunnels, with fixed stations, the subway can convey its passengers at a speed twice as great as that possible with cars of street tramways, even when these have mechanical traction.
The design of the Glasgow Subway is about a dozen years old, although the system has been open for traffic only since the beginning of 1897. The credit of the inception of the scheme belongs to Mr. Alexander Simpson, C. E., of Glasgow, whose firm, Messrs. Simpson & Wilson, have been throughout, and still are, the engineers of the enterprise. Naturally, as in all great works, there has been much departure from the original design. Mr. Simpson's first idea was for an underground cable railway, of something under three miles, between the centre of Glasgow and the adjoining burgh of Partick, -- in one tunnel only, with two sets of rails. On this plan the stations were to be equidistant, and the cars, attached to an endless chain, were to start and stop simultaneously. The engineman at the power station would alone have control over the two sets of trains, and would let out the requisite length of rope when he received signals from all the stations.
This idea was ingenious (though one can now see many objections to it), and it received the approval of the House of Lords; but the bill was thrown out by the House of Commons, in 1887. Next year the scheme took a larger form and another shape, appearing in a plan for a double line in two tunnels to connect the north and south sides of the river, as well as the districts of the previous proposal.
The Clyde Trust opposed this scheme as both invading their domain and as calculated to prevent, or obstruct, the future deepening of the river. Their opposition was successful, and the subway design was suspended until another undertaking was carried through Parliament, viz., one for a tunnel under the Clyde for pedestrian traffic. After this had established a sort of right-of-way precedent, the subway scheme was again sent up to Parliament, and in 1890 it was sanctioned, in spite of the opposition of the Caledonian Railway Company, then busy with the construction of their city and suburban underground line.
The subway line was completed in 1896 and opened for traffic in January, 1897. Under the act the Glasgow District Subway Company acquired the right, or free way-leave, to pass under, and follow, the lines of streets. But the circular design necessitated the passing under much private property, the owners of which were, or professed to be, alarmed at the prospective effect of the tunneling on their buildings. The company, therefore, had to purchase large blocks of property, which may, and undoubtedly will, ultimately yield a good return as an investement, but which have weighted the undertaking with a much larger capital than was necessary for the actual construction and equipment of the subway.
As an underground railway the subway is not remarkably deep. It is true that at one place, Hillhead, the distance from the street surface to the top of the tunnels is 115 feet, but that is because the line at that point passes under a considerable mound. At another place the depth is only 7 feet, and at one point in the centre of the city the depth is 40 feet. Averages in such circumstances do not mean much, but the average depth for the whole length of the tunnels is 29 feet from the street surface.
The tunnels are practically two endless cylindrical tubes, at slightly varying distances apart, but opening out together at each station into one large arch of 28 feet span. At suitable intervals along the tunnels are openings through which the surfacement may pass from one line to the other without returning to a station. The general curvature is very considerable, yet the sharpest curve on the line is of not more than 660 feet radius. The gradients while easy for cable traction, would be regarded steep for steam or electric power, -- those where the tunnels pass under the Clyde being 1 in 18 and 1 in 20, respectively.
The tunnels were formed for the most part on what is caled the "cut and cover" method. Where brick-clay was encountered, ordinary brick tunneling was used. In passing under important blocks of buildings and factories, the work was done by iron tunneling, sometimes with, and sometimes without, the use of compressed air. In working beneath the river the tunnels were driven under air-pressure, with such effect that the river bed was blown up about a dozen times before the crossing was completed. The cross-river tunnels are remarkable triumphs of constructive engineering under extremely difficult conditions. It is a noteworthy fact that the cross-river portions are the driest parts of the whole tunnels, -- and the subway is carried once under the River Kelvin, as well as twice under the Clyde.
A drainage system had to be constructed to carry off the water that must accumulate in all underground worings. For the section between Partick and Cowcaddens, which one may call the northwestern segment of the circle, a brick conduit was constructed, or 4 feet diameter, to run the drainage into the River Kelvin. On the section between Cowcaddens and Buchanan street, there is gravitation drainage into this conduit. On the eastern side of Buchanan street station there is a fall to St. Enoch station, where the water is pumped into the sewers.
On the south side of the river there is no natural outfall, and the tunnels cannot be drained to one or two points to be there run off or pumped up; there are, therefore, pumps at five different stations, the most important of them being at Govan. The working of these pumps, in order to keep the tunnels dry, means naturally a very large addition to the running charges of the system, but as experience has been gained the pumping is now better regulated,and will soon be done entirely by electricity.
Although the use of the cable was in the original design sent to Parliament, and was always favoured by Mr. Simpson and his partners, the Subway Company was not confined to cable traction by their bill. They were quite free to adopt any other mode of traction (except by steam locomotives), and some of the promoters were strongly in favour of electricity. It was, on the advice of Mr. David Home Morton, C. E., that cable traction was finally decided on. Mr. Morton, on being appointed consulting mechanical engineer to the company, addressed himself to a practical and exhaustive study of all the systems of traction in use in Europe and America, and found the balance of evidence distinctly in favour of the cable in the peculiar conditions on which the subway must work.
For electric traction the subway cars would have had to be made to overcome the steep gradients, incomparably more heavy than there was necessity for on the rest of the road. Then the circumference of the tunnels limits the height of the cars, so that sufficiently powerful motors could not be placed under them. This meant that electric locomotives would have had to be employed, and that implied more heavy rolling-stock and more heavy permanent way, and also more wear-and-tear.
By the cable system, on the other hand, the trains of cars, running in opposite directions, assist one another,-- those going downhill helping to pull those going uphill. By this principle of compensation much hauling power is saved, and it becomes more effective as the number of cars run is increased. Each additional electric car put on a route means a large addition to the working expenses, but each addition to the number of cars on the cable makes only a nominal demand on the horsepower. Thus the service on the cable system can be increased as the traffic requires, without appreciable increase of working expenses, while on the electric system every car put in motion becomes a heavy charge, whether it is earning money or not.
The cable system having been adopted, Mr. Morton proceeded to examine carefully all the cable systems at work in America, and out of his long and careful study of existing methods and machinery, he has evolved one of the best and most perfectly equipped cable systems in the world. While adopting every good idea he saw in use, Mr. Morton had to adapt, alter, and invent as he went along with the equipment in the subway. He had to contend with, or provide for, conditions which did not exist in any of the systems elsewhere at work. The Glasgow District Subway, as it is working today, is a striking monument of Mr. Morton's tireless energy, mechanical genius, and unfailing resourcefulness. The whole equipment was designed and constructed by him, and is still under his supervision as consulting engineer of the company.
The adoption of the cable permitted of the use of comparatively light rails on the track (60 pounds per yard), and of light rolling-stock. The sleepers of the permanent way, which is of 4-foot gauge, are laid on ballast, and the rails are spiked down to the sleepers without chairs. The distance between the top of the rails and the highest point of the roof of the tunnel is 9 1/2 feet.
The permanent way is so planned as to place every station at the summit of a gradient of about 1 in 40, and this serves several good purposes. Thus, the stations are brought more conveniently near the surface; the up-grade assists the brakes in stopping the cars; and the down-grade reduces the pull on the cable when a start is made, and enables the start to be made smoothly and quickly. The cable is carried over 1700 track-sheaves in each tunnel. On the straight track the sheaves are vertical and 30 feet apart; on long curves they are inclined; and on sharp curves they are horizontal.
On the sharpest curves both horizontal and inclined sheaves are used, at distances of eight or nine feet,-- the distance apart increasing as the curve widens. These sheaves, having to revolve at a very high speed, are of special construction in each of the three types. They are all so designed that when screwed down on the track they carry the cable at a level of a couple of inches above the top of the rails. The cable is midway between the rails in the straight track, but on curves is two or three inches off the centre line, and towards the centre of the curve, so as to prevent the "gripper" from fouling the inclined and horizontal sheaves.
The cars, which were built by the Oldbury Carriage and Waggon Company, are of the double bogie type of American pattern. Each ordinary car weighs 9 tons, but trailer cars, slightly smaller and weighing 5 tons, are now attached, the two together forming a train with connecting gangway. The interiors are roomy, with plenty of headroom (6 1/2 feet), and with so much space between the longitudinal seats that you do not rub against passengers' knees as you pass along.
The large cars are a trifle over 40 feet long, but a vestibule for the driver at one end and one for the conductor at the other, reduce the inside length to about 32 feet. These vestibules are shut off from the car by glass-panelled sliding-doors, which are opened by the driver and conductor when the car putls up at a platform. Passengers enter by the rear door and leave by the door in the front. When the car starts the vestibule doors are shut, and thus all draught in the interior is prevented. The signal to start is given by the conductor to the driver by means of an electric bell, and the side doors at each end, giving access from the vestibules to the station platforms, are closed by iron lattice-work. Entry and exit are easy, as the car floor is on a level with the station platform. Both externally and internally the cars are attractive in appearance. The interior fittings are of polished teak, with oak panels; the roof is painted cream-coloured, relieved in gold and vermilion; and the general effect is bright and fresh.
The inconvenience of noise, inseparable from cable running, is reduced to a minimum by thick layers of felt, covered by linoleum, on the floor, and by felt under the seats. There are windows all along the sides and at the ends, although there is naturally not much to be seen in a tunnel, and although there was a little trouble at the outset, the cars are now admirably lighted by electricity on the trolley system. That is to say, the current is picked up by means of trolley wheels from two continuous conductors running along the side of each tunnel. There is sitting room in each of the large cars for 48 persons, and ample standing room for as many more without inconvenience to the sitters.
Though light, the cars are very strong, steel being largely used in the construction. Bogies and underframing are of steel, and the "gripper" is secured to the leading bogie under the leading axle. Between the bogies and the car body are four sets of steel springs, but there are no springs between the bogie and the axle boxes, so as to leave room to keep the "gripper" clear of the track sheaves.
The gripper is, of course, the most important part of the car equipment, and may be described, generally, as a powerful vice, secured to the underframing, and operated by screws or levers, gripping the cable in such a way as to impart its motion to the car. The subway grippers differ from those used on the street cable lines, inasmuch as the latter have to be dropped into the conduit below the surface, while on the subway the cable runs above rail level, and the lowest part of the gripper is several inches above the top of the rails. The gripper is fixed parallel to the rails, under the forward axle of the leading bogie, enabling it to travel on the centre line between the rails; the bogie thus acts as a motor, guiding the long car.
Of the jaws, between which the cable is clamped, the lower is fixed, while the upper can be raised or lowered at the will of the driver. The cable, which must at times leave the gripper, can always be discharged from one side. The jaws, being subject to considerable wear, are fitted with renewable dies of rolled steel, giving effective lengths of 2 feet, 4 inches, and 2 feet, 9 inches, respectively, for top and bottom jaws. The upper jaw is brought down on the rope by an arrangement of links and levers, connected by chains to the driver's wheel in the forward vestibule.
The gripper appears, at first sight, to be a very intricate piece of mechanism. The apparent complication is, in reality, due to the trip-gear for the discharge of the cable from the jaws and to the duplication of levers, because of the unusual length of these jaws. The tripgear consists of a very ingenious arrangement of links, pawls and levers, whereby, even if the gripper is being held hard on by the driver's handwheel, the top jaw can be suddenly released and allowed to rise on springs clear of the cable, this act being followed by the lifting of two small discharge bars, which, in turn, raise the cable and throw it free of the gripper.
This gear is operated generally by means of a hand-lever by the driver; but should he omit to use the lever at certain points where the cable is to be released, a small roller on the forward end of the gripper comes in contact with a long cam-bar fixed between the rails, and causes the gear to act precisely as if the lever were used. At the passenger stations the cable is not thrown out, but simply runs on the lower die of the gripper, the top jaw being raised a little out of contact.
The passenger stations are fifteen in number. A penny fare covers four stations, and a twopenny fare covers the whole of either circuit. The original intention was to have a universal penny fare and no tickets, the fare to be paid at an automatic turnstile on entering a station,-- and probably this design will be ultimately carried out. It was, indeed, tried for a time, but was found to be abused by idle persons, who, having once paid, went on round and round the circle, either for the fun of the thing or for the pleasure of cheating the company. It is a question whether the great saving to be effected by dispensing with ticket-clerks and collectors would not more than compensate for any loss in that way, which, though it might be considerable when the thing was a novelty, is not likely to be much now that the subway is thoroughly familiar.
Six of the subway stations are quite underground, and have to be always electrically lighted; the others are open to daylight and have glass roofs. All of them have island platforms, about 10 feet wide, on a level with the car floors, and access to the street is by means of stairs and corridors, lined with white tiles and electrically lighted. At one station (Kelvinbridge) there is an electrically worked elevator for the use of passengers between the street and the platform, and it is intended that similar elevators will, in due time, be supplied at some of the other stations.
So much, then, for the line and its equipment. The power station is situated on the south side of the river, in a district of the city chiefly given up to engineering. The main engine-house is 138 feet long, 100 feet wide, and 31 feet high from floor to roof. Heavy cast-iron columns run down the centre to assist in carrying the girders for two 25-ton travelling cranes. The main engines are in duplicate, placed on each side of the centre line of the enginehouse, but though one may be used for each tunnel, it is found that one is sufficient for the traffic in both tunnels. One engine, therefore, is always kept in reserve, and the engines are run alternately, week or fortnight about.
Each engine is of the horizontal single-cylinder, non-condensing type, with Corliss valves. The cylinder, which is steam jacketed, is 42 inches in diameter, and the piston has a stroke of 6 feet. The steam inlet valves are actuated by means of an eccentric and rod independent of those which work the exhaust valves, while, owing to the distance from crank-shaft to valves, the eccentrics run on a counter shaft. The ponderous flywheel, 25 feet in diameter, weighs 50 tons, being built up of cast-iron hub, arms, and rim segments.
To give the maximum speed of 15 miles an hour to the cables, the engine, which is capable of developing 1500 H. P. economically, runs at 55 revolutions per minute. Two governors are provided, the larger acting on the valve gear, and the smaller on a throttle or butterfly valve immediately above the main steam inlet valve. These two governors act quite independently of each other. Midway between the two large engines is a vertical, double-cylinder engine, 14 inches in diameter by 18 inches stroke, which serves as a barring engine to assist in starting its big brothers. It is also of service for examining and repairing cables and machinery, giving a slow, steady motion, either backward or forward, under circumstances when the use of the big engine might be attended with danger. In threading the first cables, this small engine proved a valuable assistant.
Across the house runs the main driving-shaft, made in two lengths, and ranging in diameter from 18 inches to 21 inches, with all the necessary bearings and couplings arranged so that the shafting may be run by either or both engines, or that in the event of one of the cables having to be temporarily stopped, the other can be kept going. Running loose on each section of this shaft is a 26-groove rope drum, 13 feet, 9 inches in diameter.
Power is transmitted to it by means of a Walker-Weston multiplate friction clutch. This clutch consists of a series of annular plates, which are attached alternately to a casing fixed to the drum and to a sleeve fitted to and driven by the shaft. These plates are held by keys so that they cannot revolve independently of the casing or the sleeve to which they are attached, but all can slide to a certain extent parallel to the axis of the shaft. To set the drum in motion it is only necessary, by means of a hand-lever and rack and pinion arrangement, to press all the annular plates together, causing great friction between them.
The clutch-driven drum, in turn, drives two 25-foot diameter rope drums, each of which is mounted on a separate shaft, one being 18 feet in advance of the other. Of the twenty-six cotton driving ropes, which are each 2 inches in diameter, fifteen drive the first drum. Owing to the method of wrapping the steel cable on its driving-drums, the first, of necessity, does more than the second, hence the cotton rope drum which drives the second takes eleven ropes only.
A 14-foot diameter cable drum is fitted on the overhung end of each of the 25-foot drum-shafts. These are differential drums of the Walker type, with six grooves, and together drive one of the haulage cables. They are set in line so that the bottoms of the grooves of one drum are opposite to the ridges of the grooves on the other, to divide the angle of divergence in wrapping the cable. A massive strut, with wedge adjustment, between the shafts, counteracts the tendency of the cable to bring the drum-shafts towards each other.
The Walker differential drum overcomes the difficulties ordinarily experienced through the stretching and slipping of the cable and the wearing of the grooves. Coming up from the road the cable runs up the cable culvert to the under side of the differential drums, and after taking the requisite number of turns around them, runs off to a 14-foot sheave on the tension carriage, from which its direction is changed down the culvert again to the road. The tension carriage can take up a stretch of 300 feet.
The tension varies, of course, according to the number and position of trains on the cable at a time, and an Upton tension regulator is applied to meet the variation. This regulator consists of a variable number of plate-weights, slung by four long links, two of which are fixed to the anchorage, and two to a small four-wheeled carriage running on the same rails as the tension carriage, and connected to it by means of a wire rope. As the regulator carriage moves to and fro, owing to the varying pull on the cable, the weights rise and fall, and their effective value varies as the angularity of the links.
As the cable comes down the culvert on to the track it is diverted by means of a 12-foot sheave, which is placed under the rails and slightly out of the horizontal. From this 12-foot sheave the cable passes over five 30-inch vertical sheaves, which are pretty close together, and which elevate the cable about 7 inches above the rails, from which it falls back to the normal working-level of 2 inches. On returning to the station, of course, the operation is reversed, and the modus operandi is the same for both tunnels, with the necessary difterence in deflection.
The boiler house equipment consists of eight Lancashire boilers, 8 feet in diameter and 30 feet long; but only four, or at most six, are ever in use at one time. Boilers and fittings are constructed for a pressure of 120 pounds per square inch, but the regular working pressure is 100 pounds. Vicars mechanical stokers are used, and also a coal elevator connecting with the stores beneath, power for these being furnished by an 8 1/2 by 9-inch Robey high-speed engine. Over the boilers there is a maze of pipes, all neatly clad in magnesia covering, painted white. The whole place is scrupulously clean and bright.
The drudges of the system,-- the cables themselves,-- are well worth attention. They are each 1 1/2 inches in diameter and 36,300 feet in length, and are made up of six strands, of from 13 to 16 wires per strand, laid on a hemp core Both the wires and the strands are laid from left to right and not in opposite directions, as in the ordinary "lay," and thereby a greater wearing surface is presented. Each one of the cables contains about 600 miles of steel wire, and when splicing is necessary, a length of about 80 feet is taken for the splice. Splicing is carefully taught in the yard, where old cables are kept for the practice of the men, and rewards are given for proficiency in the art.
Each cable weighs about 57 tons, and one of the problems to be solved was how to get such a weight transported from the cable makers' works in the north of England to the power station. Each of the four makers who have supplied cables has adopted a different method of transport, but this is an interesting part of the story which hardly belongs to the present purpose.
At the power station is also the electric plant for lighting the whole of the line, and working pumps, elevators and other auxiliary apparatus. It consists of four Silvertown continuous-current dynamos, each coupled to a compound vertical Belliss engine with 9-inch high-pressure and 15-inch low-pressure cylinders, the stroke being 9 inches. The dynamos are of the inverted horse-shoe type, and each is capable of developing 79 kilowatts, or about 106 electric H. P. Throughout, the wiring is done on the three-wire system.
The car shed is apart from the power station, and is situated near the Govan Cross station of the subway. It is not the least interesting feature of the system, for here is a most ingenious appliance for lifting the cars bodily from, and for placing them onto, the track, without stopping the cable or interrupting the traffic. The tunnels pass right under the car shed, and access to them is through a shaft or pit, 55 feet long and 28 feet wide, and 20 feet deep, through which the cars are lifted or lowered by means of a 12-ton travelling crane. This crane acts both as an elevator, a turntable and a traverser,-- lifting the cars, carrying them where required, turning them, and dropping them on to any desired line of rails. The shed is 220 feet long and about 115 feet broad, with a storage space of over 25,000 square feet.
Between the rails, on which the cars are placed when hoisted up from the subway, are 3 foot pits, to permit of the inspection, cleaning and repair of the under-frames and grippers. The cars cease running at 11 P.M., and as each completes its run, it is taken into the car shed for the night. In case of damage or accident to any car on the circuit it can be run (or if its own gripper is disabled, it can be pushed by the car behind) to the car pit and there taken off the line without delaying the traffic more than a moment.
Although the system is worked according to Board of Trade regulations, on the block system, that system is practically automatic and signalmen are dispensed with. At each station there is a semaphore, at the end of each of the tunnels as it opens out into the arch. These show red and green lights, which signify to the driver of the incoming car whether the line in advance of him is clear or not. When the preceding train has left the station in advance the starting signal is given, and as soon as the train has gone its own length into the tunnel it passes over a treadle which breaks the electric contact and sets the signal behind at "danger," at which it must remain until the train, on passing the next station, acts on another treadle, which releases the danger signal and shows the line to be all clear between the two stations.
The stations are also connected by telephones and electric bells, and each station is also in communication with the power station, and can signal for the stoppage of the engines there in case of need. Practically, then, the "blocks" are the stations, and therefore the frequency with which trains can be run is limited by the distance between the blocks, as no train can leave a station until the train in advance is starting from the next station.
At present the trains are run at intervals of three and a half minutes, and this is about as close as they can get under the present arrangement of blocks. A more frequent service, however, could be maintained were the signals put midway in the tunnels between stations. And here it may be mentioned that, although the Board of Trade insist upon this blocking and signalling, many competent authorities think the whole system unnecessary and unnecessarily expensive. It is argued that the cars do not run at a rate of speed which would permit of any serious accident, even if one did run into the rear of another. And they cannot run into each other going in opposite directions. Each car is furnished with such powerful head-lights that the driver can see a long way ahead, and could always stop his own car before he could run into a disabled one ahead.
In relation to the street tramways the subway is undoubtedly handicapped. The working charges laid upon the subway (which do not fall upon the street tramway) in respect of the Board of Trade regulations, the blocking and signalling, and the limitation of trains by the block, are very onerous. And then the subway has heavy special expenditure in connection with lighting and pumping; while, being a novel undertaking, the staffs in all departments are kept much larger, and therefore at more expense, than there will be need for when every item in the system has been thoroughly tested by experience. Yet with all these financial drawbacks in comparison with competing systems, the subway is not only paying, but promises to be a highly remunerative undertaking as traffic increases and working expenses are reduced, as they are sure to be in the near future.
As a means of locomotion the subway is comfortable, for the movement of the cars is without spasmodic jerks, and the gradients are scarcely felt. There is necessarily some noise from the running of the cable, but it is minimised to something very much less than that on probably any other underground railway. The steady weekly increase in the traffic receipts may be taken as proof of the growing popularity, and therefore efficiency, of the service.
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