By Daniel Kinnear Clark
Tramways: Their Construction and Working, Embracing a Comprehensive History was written by Daniel Kinnear Clark and published in 1894. Here is Chapter VI, on Cable Traction. The section on the Edinburgh Northern Cable Tramways was written by William Newby Colam, an engineer who participated in the construction of several UK cable tram lines.
From Tramways: Their Construction and Working, Embracing a Comprehensive History, Incorporated Association of Municipal and Second Edition, 1894. (London, England).
The working of tramways by cable haulage is effected by the employment of an endless wire rope continuously moving in one direction, supported on pulleys within a slotted tube laid below the surface of the street or roadway, or between the rails of a surface or an elevated railway. The rope is driven by means of a fixed or stationary steam-engine or other motor, situated at a suitable place near the line, the motion of the cable being intermittently communicated to the cars, for starting and stopping, by means of a gripper attached to the car.
The principle of cable traction has been successfully applied on railways and in mines for many years. The first practical test for cable traction was made in San Francisco, in 1873, by Andrew S. Halliday (Hallidie - JT) and his associates, A. E. Hovay (Hovey - JT), W. Eppelscheimer (Eppelsheimer - JT), and Henry Root. For heavy street traffic the cable is extensively employed.
The slotted tube is of concrete. It is virtually an arch of which the key is left out. It is constructed with yokes or frames of angle-iron or cast-iron. The latter material is preferred. The sides act as cantilevers to resist the lateral pressure of the soil, packed by heavy waggon traffic, and, in cold climates, the pressure in addition due to the expansion of the soil by freezing. The first tube was 12 inches wide, 15 inches deep, or 22 inches below the level of the street. The slot is usually 3/4 inch wide, and it is formed by two slot rails which are fastened to the yokes at the upper side. The slot rails, of overhung formation, are brought up to the surface level and require to have great vertical and lateral strength, whereby they are nearly as heavy as the way-rails.
The gripper is a powerful vice within the tube, supported by or suspended from the car by means of a thin shank through the slot. It is worked from the platform by a lever or a handwheel through the medium of an eccentric toggle-joint or an equivalent device, and is caused to grip the rope with a pressure sufficient to impart the motion of the rope to the car. The rope is grasped between two flat plates or jaws, upper and lower, usually of steel, and from 18 inches to 20 inches long, lined with removable dies for wear, slightly grooved to fit the rope. Grips are of two types -- vice-grips and roller-grips. The former comprise the side grip, the top grip, the bottom grip. Side grips are usually constructed with a pair of jaws at each side of the shank. They take the rope on either side without turning the cars.
The cable is a steel wire-rope, commonly of 6 strands twisted round a heart of hemp rope, each strand of 19 wires, of which 7 wires form the heart of the strand, round which the other 12 wires are wrapped. Sometimes the 12 enveloping wires are larger than the 7 heart wires to provide allowance for wear. Ropes are also made with 6 strands of 16 wires each, or 7 strands of 19 wires, usually laid 12 over 6 over 1. On straight lines 19 wires do good service. Ropes are also made with a wire centre. Though stronger than others they are not so flexible.
Cables are from 1 inch to 1 1/2 inches in diameter. The usual sizes are 1 1/2 inches and 1 1/4 inches. The 1 1/4-inch ropes weigh 2 1/2 lbs. per foot, and their breaking weight is about 80 tons. The average life of common ropes is 12 1/2 months, or 88,402 miles, making about 85,000 miles per year. The general average life for all lines and ropes is about 8 months, or from 40,000 to 150,000 miles. According to the system of wire rope known as the Lang lay the wires forming the strands, and those of the strands themselves, are laid in the same direction instead of in opposite directions Thus, a larger portion of each outside wire is exposed for wear, the rope is of greater flexibility, and a maximum degree of wear is attained without fracturing of the wires.
The driving machinery operates on the rope by frictional contact with two large V-grooved pulleys in tandem, usually lined with wood or with babbit metal. The rope makes two wraps over the pulleys, like the letter S, known as the front driver and the back driver. The pulley shafts are geared together by two spur-wheels, one of which is driven by a toothed wheel on the engine shaft. Frictional contact is maintained by tension apparatus, in which a large sheave is mounted on a car which travels to and fro on a track laid over a long, narrow pit. A tail rope or a chain is connected to the car, and is led over a pulley, suspended within a deep well, and loaded with a heavy weight, which, taking up the slack, maintains tension on the cable. The length of the track is from 150 feet to 200 feet for long lines. The length of the tail rope is adjustable by means of hand-wheel and worm-gear on the car.
The steam-power is from 200 to 1,500 horse-power in duplicate, averaging 25 actual horse-power per car, including reserve. In Melbourne, Australia, the aggregate length of cable is 91 miles. There is 15 horse-power per car of the average number of cars running. On American lines there is an average of 4.6 horsepower to move 1,000 feet of cable. The power required to move the cable alone is from 35 per cent, to 75 per cent. The average of twelve roads is 54 per cent. The approximate "steam horsepower" to work a line employing less than 10 miles of rope may be estimated as follows :-- Allow 4 horse-power to each 1,000 feet of rope, reckoning each right-angle curve equivalent to 1,500 feet of straight way. Add 3 horse-power for each car of ordinary size, and 60 horse-power for engines and machinery.
Cable Tramways In San Francisco And Chicago.
Several tramways are in operation in San Francisco. Of these, the Clay Street Tramway has a double way, about 5,500 feet, or 1.04 miles in length, of 3 1/2 feet gauge. It rises to a height of 307 feet above the starting-point, in the course of 2,475 feet, making an average gradient of 1 in 8, the steepest gradient being 1 in 6. On the other tramways of San Francisco there are gradients of 1 in 5, on which cars are drawn upwards and downwards with ease and security. A car with its coupled dummy in front, when fully loaded, hold together 44 passengers.
The disposition of the dummy car, tube, and gripping apparatus is shown in Figs. 314 and 315. Below the surface, and about the middle of each way, there is a channel, or technically a tube, within which the endless rope travels on pulleys. The tube also affords protection for the gripper A, connected to the dummy on the way by means of a flat bar of iron which passes up through the longitudinal slot in the upper part of the tube. The throwing of the gripper into action, by grasping the rope, induces the necessary motion of the car, which, of course, travels at the same velocity as the rope. The slot is not immediately over the centre of the tube, but on one side, in order that grit or other droppings falling through the slot does not lodge on the rope, but falls to the bottom of the tube. By this means, also, the gripper passes by and under the upper pulleys, C, Fig. 315, and over the lower pulleys, D, Fig. 314 in the tube.
The rope, endless, travels down one way and up the other. At the summit the rope is turned on to one series of 8-feet pulleys, and led into the engine-house. Thence it passes out by another series of 8-feet driving pulleys, the rope making a right-angle turn to the left and right after leaving the house. At each terminus of the road the rope passes half round an 8-feet horizontal sheave, fixed to a tension-carriage moveable horizontally, for the purpose of maintaining uniform tension on the cable. The pulleys D, Fig. 314. by which the rope is supported in the tube, are from 11 inches to 12 inches in diameter, secured to cast-iron standards placed 30 feet apart, with man-holes and doors for access. The sheaves on the Chicago road are formed in halves bolted together, with wood between, the dividing plane being at right-angles to the axle of the pulley. The wood thus forms the bottom of the groove, and is exposed to the wear. It is renewed every two months. The slot-rails are supported by intermediate cast-iron standards, placed at from 3 feet to 4 feet apart, and they are fixed at a distance of 3/4 inch apart, transversely, forming the slot. Sheet-iron tubing, E, Fig. 314, about 10 inches wide, reaching upwards to within 15 inches of the surface of the street, is bolted to the cast-iron standards. The tubing is packed outside with earth, and, to prevent the earth from getting into the tubing, a 3-inch plank, F, Fig. 314, is placed on edge on the standards, the upper edge being at the level of the underside of the slot-rail. The running rails are laid on longitudinal wood sleepers, about 3 3/4 inches wide, 5 1/2 inches deep, and these are let into and supported by short cross sleepers, the inner ends of which have a bearing on the standards, and are bolted to them.
According to another system of construction in San Francisco the standards are formed from ordinary railway-bars, bent as required, braced and arranged to carry both the slot-rails and the running rails. A culvert, or "tube," of Portland-cement concrete is constructed in place of sheet-iron tubing.
Where a steep rise occurs in the road, the wire rope is kept down by small pulleys, as shown in Fig. 315, from 6 inches to 8 inches in diameter, mounted in a frame. Where the rope leaves a summit and descends, it is passed over a pulley of about 4 feet in diameter.
The cable is about 11,000 feet in length, 1 inch in diameter, of crucible steel wire, of 6 strands of 19 wires. Each wire has a tensile strength of 160,000 pounds, or 71 tons, per square inch. It can be bent in any direction without fracture. The wire rope is found to stretch 1 per cent, of its length before being too much weakened for use. The average life of the rope is about fifteen months. On some tramways the length of rope is 17,000 feet. A tensional-pulley system is provided in the enginehouse, about 50 feet in length.
The shank B of the gripper A, Fig. 314, is, as before noted, a flat bar of iron 5 1/2 inches wide, 5/8 inch thick, which works through the longitudinal slot, and to the lower end of which the gripper attachment is made. This consists of two pairs of 3 1/2-inch pulleys, placed obliquely, the pulleys of each pair being 10 inches apart and secured to sliding frames, mounted with jaws for the purpose of taking a firm hold of the rope. The small sheaves act as guides for the rope to pass between the jaws, and they are gradually tightened on the rope by the screw G. The dummy, through the medium of the shank and pulleys, gradually acquires the velocity of the rope until the gripping jaws are brought into action, and firmly acquires a hold of it by means of the screw G.
The speed of the cable is 6 miles per hour, running for 16 hours a day. It is driven by two horizontal steam-engines, each of 100-horse power, of which one is kept in reserve; and about 2,900 pounds of small coal is consumed per day. The total cost of the engines and machinery was about £3,000. A double way of the tramway, having a tube 30 inches deep, costs, on an average, £10,000 per mile, not including rolling stock. For a tube 12 inches deep the cost would probably be £8,000. It is believed that a gauge of 3 1/2 feet is as effective as the 5-feet gauge, and is frequently more convenient. The dummy carries 18 passengers, the car 26; together, 44. Each vehicle is provided with a powerful break (brake -- JT).
Many of the cable roads have right-angle curves, for which the rope is deflected by means of two horizontal 8-feet pulleys, with other auxiliary pulleys.
HlGHGATE-HILL CABLE TRAMWAY, LONDON.
The Highgate-hill cable tramway was the first cable line constructed in this country. The works were carried out by the Patent Cable Tramways Corporation, under the supervision of Messrs. Eppelsheimer and Colam and the line was opened in May, 1884. It is nearly 3/4 mile in length, of double way, constructed to a gauge of 3 1/2 feet, between the Archway Tavern, Upper Holloway, and Southwood Lane, near the summit of Highgate-hill.
The gradients vary from 1 in 11 to 1 in 15, and the curves from 250 feet to 3,000 feet in radius. The way was laid with steel rails of the Dugdale type, weighing 52 pounds per yard. The cable consists of crucible steel wire, in strands closed round a hemp core. It is 3 inches in circumference, or 15/16 inch thick, and it weighs about 5 tons complete. It passes round two 8-feet pulleys at the termini, in brick pits. The endless rope is carried on pulleys beneath the track, in a "tube" of concrete, 10 1/2 inches deep, 8 1/2 inches wide. It is driven by two independent horizontal steam engines, each of 25 nominal horse-power, affording service in duplicate. The speed of the rope is from 5 miles to 6 miles per hour.*
* Since the above paragraphs were written, the line has stopped working.
EDINBURGH NORTHERN CABLE TRAMWAYS.
The gauge of the ways is 4 feet 8 1/2 inches. The two lines start from Princes Street, one in Hanover Street, the other in Frederick Street. The first named, or Trinity route, passes Henderson Row, where the cables branch off to the engine-house. It takes 18 curves, varying in radius from 80 feet to 980 feet, the smallest curve being less than a right angle. It is also diverted at various places by nine large pulleys. The total height ascended is 187 feet. The double way is 1 1/2 miles long. It is almost entirely on gradients, varying from 1 in 11 to, for the greater part, 1 in 60 approximately. Fig. 316 is a gradient diagram ot the line.
The gradient diagram, Fig. 317, that of the Stockbridge route, on which the steepest gradient is 1 in 13. The length of way, double line, is 1.20 mile. After passing over 100 feet curves into the Royal Circus, the line is almost entirely a series of curves, passing through steep and very narrow roads. At Stockbridge, where the cable leaves for and returns from the engine-house, the line, though curvy, is nearly level. The cable traverses 28 curves of radii varying from 80 to 400 feet. It is diverted by means of nine large pulleys. The line rises 173 feet. The tramways were opened in January, 1888.
The road is shown in section by Figs. 318 and 319, having two lines of way. The conduit or "tube" is of concrete ; it is 19 inches deep from the surface and 9 1/2 inches wide. Cast-iron tube-frames are embedded in the concrete, at 3 1/2 feet apart between centres, to which the slot-rails are bolted, forming a slot 5/8 inch wide. The frames are 1 inch thick in the webs, and they weigh 135 lbs. each. They are lined up in place before the concrete is poured in. Thus a solid mass is constructed, by which subsidence or closing, of the slot, is prevented. The extreme depth occupied by the tube is 26 inches below the surface. The bottom of the tube is 7 inches thick, the sides 6 inches, and the concrete floor of the way, 5 inches. A 6-inch clay pipe is laid under the bottom of the tube, by which it is drained from recesses in the concrete in which the supporting pulleys are mounted at 50 feet apart between centres. On two of the worst curves, there are convenient subways between the two lines of way, from which pulleys may be renewed or adjusted.
The running rails are of girder type, 6 inches deep, of steel, weighing 75 lbs. per yard. The slot-rails are fished with plates weighing 34 lbs. each. They are tied to the running rails by adjustable bars to keep these accurately in gauge with the slot. The supporting pulleys, Fig. 320, are of cast iron, 14 inches in diameter, V-shaped in the tread. The journals revolve in boxed lignum-vitae bearings. The horizontal supporting pulleys for curves, Fig. 321, are 14 inches in diameter. The large diverting pulleys are of cast iron ; the jaws are bolted on in segments, with good treads. The terminal pits, Figs. 322 and 323, holding the diverting pulleys, are, one of brick, the other of concrete. They are 19 feet long, 11 feet broad, 8 feet deep. The roofing is constructed of rolled joints, jack arches, and buckled plates.
The cables are those known as the Lang lay. This rope gives a maximum quantity of wear without fracture of wires, as it admits of the use of comparatively larger wires, and is, at least, as flexible as the older system. The rope is of crucible or steel wire laid round a hempen core, in 6 strands, each of 13 wires -- 7 round 6. The wires have stood a tensile stress of 80 tons per square inch, and torsional tests of 35 twists in 8 inches of length. The lay of the rope is 9 inches, the circumference is 3 1/2 inches, and the diameter is 1.03 inches.
The gripper, with details, is shown in Fig. 324. "The driver, in operating the hand-wheel, raises or lowers a nut by the square-thread spindle. Attached to the nut are two rods which raise or lower the bottom jaw of the gripper, the upper portions of which slide through openings in the plate, which has the upper jaw casting bolted to it. This plate rests on angles suspended from the bogie axles of the cars, and is firmly held down in its place by wedges which are forced in or out by the driver through screw spindles and inclined slots. When the wedges are withdrawn the whole gripper will rise by the action of the hand-wheel. The bottom jaw can be lowered out 6 inches, and by that means the cable can be picked up, because when the rounded bottom of the jaw touches it, the cable ascends into its place in the gripper.
The dies by which the cable is gripped, are of the softest cast-iron, and they last on an average about six weeks. The sectional area of the steel shanks where they work in the slot is 4.92 square inches.
The cable is driven by a pair of horizontal non-condensing steam-engines, having 20-inch cylinders, with a stroke of 40 inches. The Proell automatic expansion gear is employed. Either engine is capable of working the two routes, and one of the routes can be thrown off without interfering with the other. The driving pulley is 10 1/2 feet in diameter, having a V-groove. The jaw of the pulley is removable in segments, and is lined with white metal, which is renewed when the groove wears to the bottom. The bottom of the V is filled with soft wood upon which the cable bottoms. The cable, on entering the engine-house, goes direct to the driving-pulley, on which it makes a three-quarter turn, and thence passes over a 10-feet pulley to the automatic tension-pulley, around which it takes a half-turn when it leaves the engine-house. The effective tensional weight is 7 cwt.
Mr. Colam summarises the working conditions as follows :-- On gradients as steep as 1 in 11; over perfectly flat roads; round small right-angled curves; over old bridges, in which the crowns are not twelve inches from the road surfaces; two routes at considerable distances apart, worked from one engine in the same depot ; single lines with passing places; reduced speeds by auxiliary cables, when it is necessary to go round dangerous corners.
The cost of constructing and equipping these lines for a three-minutes service of cars has been as follows :
The cost is at the rate of £9,867 per mile of single track, including equipment for three-minutes service of cars.
Following on their experience of the working of the Edinburgh Northern tramways for a period of six years, the Edinburgh Corporation have lately purchased the horse tramway lines within their city boundaries, and have determined to work them by cable traction. For this purpose they have leased the lines to Messrs. Dick, Kerr & Co. for a period of twenty-one years. Practically, therefore, the whole system will in due course be converted and worked by means of cables.
It may also be noted that the tramway committee of the Newcastle Corporation have made a report in favour of the working of their system by cable traction, and there is little doubt that cables will soon be laid in that city. Other cities are enquiring in the same direction, and awakening to a knowledge of the advantages of the cable system, and its capacity for dealing with their heavy traffics : facts which for a considerable period have been fully appreciated by the cities of America and Australia, where heavy traffics have had to be negotiated.
** In a paper read before the Association of Municipal and Sanitary Engineers of Great Britain.
BIRMINGHAM CABLE TRAMWAY.
The Birmingham Cable Tramway -- a section of the Birmingham Central Tramways -- was constructed between Colmore Row, Birmingham, and Hockley, to the designs of Mr. Joseph Kincaid and Mr. E. Pritchard, the engineers of the line; and was opened in March, 1888. Fig. 325 is a plan of the Birmingham terminus in Colmore Row, showing two lines of way, connected by two over-crossings, with the position of the large terminal pulley and pulley-pit. The pulley and its dispositions are shown in Fig. 326. So also are the four large pulleys and pulley-pit at Hockley in Figs. 327, 328, and 329, which receive the ropes on their way to Birmingham, and those for working the line from Hockley to Handsworth. A longitudinal section of the engine-house and tensional gear is given in Fig. 330. The rope coming from Birmingham enters the engine-house at a low level, and passes under and free of the first driving-pulley to the second driving-pulley, by which it is received, and round which it is bent, whence it passes over the top, then crossing over to and winding under the first pulley. Thence the rope, passing from the top of the first pulley, proceeds to and passes over and under the pulley on the tension-carriage, from which it returns to the engine-house, and passes out for Birmingham. The axle of the tension-pulley is not horizontal, and the pulley is inclined. By this means the rope coming from under the pulley is diverted to one side a little, and passes by the side of the driving-pulleys in the engine-house. The same system of communication is employed for the Handsworth line.
A winch is mounted on the tension-carriage, from which a rope is led to a small pulley fixed to a cross-head, then round the small pulley and back to the winch. Strong volute springs are fixed at the back of the cross-head to take up or absorb any violent shock. From this point chains are led over the pulleys and supports, and connected to cradles, in which the tension-weights are carried. There are 16 weights adjustable in number according to the magnitude of the traffic or the condition of the rails.
The line is worked by steam-power, for which steam is supplied by six Lancashire boilers, 6 feet in diameter, 24 feet long, with two flues 28 1/2 inches in diameter, generating steam of 80 lbs. pressure per square inch. The two flues merge in one wide flue, which is fitted with 21 Galloway tubes. The chimney is 110 feet high above the ground level, and 5 1/2 feet in diameter at the top.
The engines, Figs. 331 and 332, are a pair of horizontal steam-engines, having jacketed cylinders, 24 inches in diameter, with a common stroke of 4 feet, making 50 revolutions per minute. The fly-wheels are 15 feet in diameter, 2 feet wide, and weigh about 8 tons each. Under each fly-wheel a powerful steam-brake is fixed, and the engines can be stopped immediately in case of accident to the rope. The main shaft is of steel, having 9 1/4 inch journals. The pinion on the main shaft is 5 feet 4 5/8 inches in diameter, and gears into the front driving spurwheel, which is 13 feet 11 1/8 inches in diameter. The back driver, of equal diameter, gears with and is driven by the front driver. Either engine can be coupled or uncoupled as required by means of clutches on the engine-shaft. The three spur-wheels are keyed fast on the shafts, but the large grooved pulleys are made fast or loose on the spur-wheel shafts by means of clutches and hand-wheels on the ends. The lower of the rope-driving pulleys are 10 feet in diameter. They are for the Birmingham service. The periphery is grooved for the rope, and is lined with compressed beech-wood, held in position by segments bolted on at one side, as shown in Fig. 333. The upper of the large grooved pulleys, 13 feet 4 inches in diameter, are employed on the Handsworth service. The larger size was adopted because the cars may be run on this service at a higher speed.
The cars are constructed with two bogies. They can carry 20 passengers inside and 21 outside ; together, 41 passengers.
A cross section, typical of the whole of the way, is given in Fig- 334. The gauge is 3 1/2 feet. The running rails are of girder section, weighing 98 lbs. per yard, the slot rails are 65 lbs. per yard. The conduit is of concrete, in which the framed bearers of the rails, running and slot, with the ordinary conduit-pulley supports, are embedded. The conduit is 13 inches wide, and 2 feet 8 inches deep below the level of the rails. The framing, or skeleton ot the conduit, is constructed of T-steel, 4 inches by 3 inches by 1/2 inch. The frames or yokes are 4 feet apart between centres. The carrying-pulleys, in the lower part of the conduit, for supporting the rope, are 11 1/2 inches in diameter, 3 inches wide.
The cable is of steel wire, 3 5/8 inches in circumference, or about 1.08 inches in diameter. The cable contains 6 strands of 19 wires each, laid on a central hemp-core. The wire is No. 15 wire gauge. The breaking tensile strength of all except the central wire of each strand is 95 tons per square inch, and the breaking strength of each cable is 33 tons.
The gripper, with its mounting, is shown in Figs. 335 and 336. Its position relative to the slot-rails is shown in Fig. 335, the upper part of the figure showing the slot-rails in section. When the gripper jaws are open, and the cable runs freely between them, it is carried by the smaller rollers, which are carried by levers, which work on the pins, as fulcra, and are connected by a pin, which causes them to act in concert either in raising or in lowering the rope, and so fixing or freeing it. When the lower jaw descends, with the vertically sliding plate to which it is fixed, the helical spring, acting vertically under compression through the pin and levers, forces the rollers upwards into the positions shown. The gripper-plate slides between guide-plates. By reverse movements the rope is lifted on the lower jaw into gripping position. The raising and lowering of the gripper apparatus is effected by means of the grip-lever on the platform of the car. The rope is shown in section in the two extreme positions in Fig. 334 ; the upper position when gripped, the lower when running free.
The cable tramway, as above described, has been extended from the Hockley winding station on a route three miles long with double way, worked by ropes from the Hockley station.
MATLOCK CABLE TRAMWAY.
The Matlock Cable Tramway, opened in Easter, 1893, is a short line 5/8 mile in length, presenting unique features of construction and application much appreciated by the residents in the district. The track is all single line, with one passing place, and on the single line are six curves from 180 feet to 1,000 feet in radius. The average gradient is 1 in 7.7, and the steepest is 1 in 5. There is a rise of 300 feet in 770 yards. The width of road is in many places only 20 feet. Car brakes are provided of sufficient power to stop a loaded car on the steepest grade when running free after having left the cable. Each car is provided with two brakes, a wheel and a rail brake. The construction of the track is similar to that of the Edinburgh Northern Cable Tramways, but special pulleys were designed to take the cable round the curves. The gauge of the way is 3 1/2 feet. The speed of the rope is 5 1/2 miles per hour.
The driving plant at the depot is in duplicate, and consists of two Sinclair boilers fitted with mechanical stokers, and a pair of high-pressure steam-engines with cylinders of 14 inches diameter and 28-inch stroke, with Proell valve gear. The grip pulley, cable gearing, and car grippers are similar to those supplied for the Edinburgh cable lines. The cars are double-deckers, and have garden seats both inside and outside, seating 31 passengers. The whole of the permanent way, engines, boilers, cars, and cables were provided through Messrs. Dick, Kerr & Co. to the designs of Mr. W. N. Colam. Mr. Croydon Marks was engineer to the company.
BRIXTON CABLE ROUTE OF THE LONDON TRAMWAYS.
(Note: Figures referred to in this section are not available. - JT)
The Brixton Cable Tramway of the London Tramways Company has a track length of 5 1/2 miles, to a gauge of 4 feet 8 1/2 inches ; and runs from near Kennington Park through the busy thoroughfares of Brixton, up Streatham-hill to a point near Streatham-hill Station. The depot, situated at the Streatham terminus, is of large dimensions, covering a piece of ground 370 feet by 110 feet. Its arrangement is shown in detail in Figs. 337 to 339 (Plates V. and VI.). It was built to accommodate the machinery and cars necessary for working an extension of the line to Streatham Common : a further distance of about three miles of route. The London tramway line was opened for horse traffic about the year 1875 ; and the cable tramway from Kennington to Telford Park, in December, 1892.
The cable, about six miles in length in one rope, was manufactured of special steel, and it weighs about 30 tons. It runs along the road in a concrete tube, constructed centrally along both up and down tracks, somewhat similar to the arrangement in the case of the Edinburgh tramway shown in Figs. 318 and 319 (page 535). The tube, which is properly drained, is 19 inches deep and 9 inches wide. In the road, however, there is but a continuous slot 5/8 inch wide; this slot being formed by rolled steel slot-rails fixed to cast-iron yokes embedded in concrete. The speed of the cable is 8 miles per hour.
In the tube on the straight road, at intervals of about 50 feet, vertical pulleys, as in Fig. 320, are placed, and on the curves horizontal pulleys (Fig. 321). at intervals proportionate to the curves. These pulleys carry the cable so that normally it is from 1 1/2 inches to 2 1/2 inches out of the centre line of the slot: no road dirt, therefore, falling on it.
Over each pulley a hatch cover (Fig. 319) 18 inches by 9 inches, is placed in the road. This cover is fitted with wood blocks, and is very little distinguishable from the ordinary paving.
At the Kennington terminus, large pulleys are provided for the purpose of passing the cable from the up line to the down line, similar to Fig. 322 (p. 538). At Streatham, similar pulleys are provided to pass the cable into the depot.
Ordinary horse cars are employed on the line for passenger traffic, coupled to a cable car for the purposes of cable traction. On the cable car the gripping apparatus is mounted. Such a disposition was rendered necessary by the fact that at Kennington the passenger cars are despatched to three different termini by means of horses, and it was thought undesirable to increase the weight of their cars by the gripping apparatus. The cable cars simply carry the gripper and the driver, the Board of Trade objecting to their carrying passengers until after the line had been in operation for some time.
Each cable car is provided with a double-jawed gripper, somewhat similar to Fig. 324--that is, a gripper which is capable of use on both the up and the down lines. The gripper is suspended from the car framing in such a way that it is free to move from left to right: a movement which is necessary when rounding the curves in the slot. The shank, which is 12 inches wide and 1/2 inch thick, passes through the slot, and is fitted with upper and lower jaws for gripping the cable. The upper jaw maintains a fixed level in the tube; whilst the lower jaw can be raised or lowered by means of the hand-wheel and screw, as seen, above the car floor, to the extent of 6 inches, thus rendering it possible to pick up the cable at any part of the road. Both jaws are lined with soft cast-iron dies, which are easily renewable. In rounding curves in the road a horizontal roller is provided in the gripper shank, and this then rolls on a recess in the slot rail.
There are four double-furnace Babcock & Wilcox water-tube boilers, having a working pressure of 140 lbs. per square inch. They are provided with Vicars' mechanical stokers and coal elevators ; also an automatic arrangement for maintaining the steam steadily at one pressure without interference on the part of the man in charge. The arrangement is worked by a jet of steam from the boiler in such a way that as the pressure rises above the normal working pressure the stokers are stopped, and when it falls the stokers go on. Rain-water is collected in settling-tanks.
The engines for driving the line are in duplicate. There are two pairs of high-pressure compound steam-engines with high-pressure cylinders of 20 inches, and low-pressure cylinders of 32 inches in diameter respectively, and the stroke of both is 50 inches. Each pair of engines is capable of driving 12 miles of cable with the necessary cars, and is now developing about half its maximum power, the high-pressure cylinders alone being used. One pair of engines is placed at each end of the first motion-shaft, the two cylinders driving on to a U crank and a disc crank respectively. The valve gear on the high-pressure cylinders is of the Proell type ; the low-pressure cylinders are fitted with Corliss valves. The motion of the engines is communicated to the counter or cable shaft by means of a rope-drive, which forms the chief feature of novelty in the engine-house. The ratio of the gearing is three to one, and the large wheel on the countershaft is 30 feet diameter. Each wheel is grooved for twenty-four 6 1/4-inch ropes, 2 inches in diameter.
A rope drive was installed instead of gearing in order to insure a minimum of vibration and noise, the depot being built in a residential neighbourhood.
At one end of the countershaft is a Mather & Platt clutch of the outside grip pattern, which can be worked by means of a lever placed near the engine stop-valve, thus insuring complete control of the machinery from one point The clutch communicates the motion of the countershaft to the grip pulley, the pulley which moves the cable. A similar clutch and pulley are to be placed on the other end of the countershaft to drive the second cable when the extensions are made. The grip pulley is of the solid jaw type ; the jaw being a parallel groove running round the pulley, the cable resting on a small shoulder on either side of the jaw. The jaw, formed of white metal slabs cast in place, and renewable, is found not to do any harm to the cable. This method of drive should be contrasted with the present American practice--two Walker differential drums having three or four complete wraps of the cable, whereas a three-quarter lap is found to do the work in London, and has been found equal to any strain put on it. The cable, after leaving the grip pulley, is conducted by another wheel to the tension pulley, which is mounted on a wrought-iron carriage free to run on rails. A uniform tension is maintained on the cable by a weight suspended from the back of the tension carriage. The rise or fall of this weight is a perfect indicator of the amount of strain on the cable, and by watching its movements a very good idea may be gained of the fluctuations of the load which have to be provided for in a cable tramway, in order to insure the smooth and steady running of the cars on the road.
The depot is built on a level 10 feet above the level of the main road, and the cars in returning to the shed have to mount a long incline of 1 in 20. An auxiliary rope is provided here, which is driven by a clutch on the countershaft, at a speed of about 2 1/2 miles per hour. It is so arranged that the cars can take this rope on the main line, mount the incline, and pass on to a traverser which commands the whole width of the car-shed, and is moved by another rope off the main engines.
Machinery is provided for changing the cables on the main line, together with the necessary storage drums. Machines are also provided for doing all necessary repairs, such as slotting, planing, drilling, turning. The necessary power for driving all this machinery is obtained from the barring engine.
A travelling crane is provided; of 55 feet span to lift 24 tons on two winches. This crane travels the whole length of the engine-house, which is 150 feet.
Mr. W. N. Colam was the engineer for the whole of the work, including the buildings; Messrs. Dick, Kerr & Co. were the contractors for the road, gripping gear, engines, and most of the machinery; Messrs. Babcock & Wilcox supplied the boilers; Messrs. Cradock & Co. the cable; and Messrs. Lucas & Aird the buildings.
The Company possess in their Brixton route one of the most complete installations for cable traction. They have applied to Parliament for an extension.
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Last updated 01-September-2010