A. RAILWAYS - HISTORY (cont.)
In the employment of steam-power for traction on railways rapid progress was made in response to the demand for power. The year 1829 is famous in the annals of railways not only for the opening of the Liverpool and Manchester line but for the invention and construction of the first high-speed locomotive of the standard modern type. Robert Stephensons engine, the "Rocket," was made under competition for the Liverpool and Manchester Railway, and it gained the prize for lightness, power, and speed awarded by the directors. The two steam-cylinders of the "Rocket" were 8 inches in diameter, with 16 1/2 inches of stroke, and the driving-wheels were 4 feet 8 1/2 inches in diameter. The engine weighed 4 tons 5 cwt., the tender following it 3 tons 4 cwt., and two loaded carriages drawn by it on the trial 9 tons 11 cwt.: thus the weight drawn was 12 tons 15 cwt., and the gross total 17 tons. The pressure of steam in the boiler was 50 lb per square inch. An average speed of 14 miles per hour was attained, the greatest velocity being 29 miles per hour; and the boiler evaporated 18 1/4 cubic feet, or 114 gallons, of water per hour. The "Rocket" possessed the three elements of efficiency of the modern locomotive,the internal water-surrounded fire-box and the multitubular flue in the boiler, or a number of small tubes in place of one large tube; the blast-pipe, by which the waste steam of the engine was exhausted up the chimney; and the direct connexion of the two steam-cylinders, one on each side of the engine, with the driving or propelling wheels, on one axle. The subdivision of the single large flue, up to that time in general use in locomotives, into a number of small tubes greatly accelerated the generation of steam without adding to the size or weight of the boiler. But the evaporating tubes would have been of little avail practically had they not been supplemented by the blast-pipe, which, by ejecting the steam from the engine after it had done its work in the cylinder straight up the chimney, excited a strong draught through the boiler and caused a brisk and rapid combustion of fuel and generation of heat. The heat was absorbed with proportional rapidity through the newly applied heating-tubes. The blast-pipe, thus applied, in conjunction with the multitubular flue, vastly improved the capacity and usefulness of the locomotive. And, taking into account the direct connexion of the steam-cylinder with one axle and pair of wheels, the improvements were tantamount to a new and original machine. The "Rocket" subsequently drew an average gross load of 40 tons behind the tender at a speed of 13.3 miles per hour. The old Killingworth engine, one of the earlier type of locomotives constructed by George Stephenson, weighing with its tender 10 tons, could only work at a maximum of 6 miles per hour with 50 tons.
For many years engines belonged to two general classes. In one class there were six wheels, of which one pair was placed behind the boiler, typified in the engines of the day made by Robert Stephenson; in the other class there were but four wheels, placed under the barrel of the boiler, leaving the fire-box overhung, typified in the engines made by Bury for the London and Birmingham Railway. Experience demonstrated the disadvantage of an overhanging mass, with a very limited wheel-base, in the four-wheeled engine running at high speed; and now it is the general practice to apply six wheels at least to all ordinary locomotive stock. The earliest four-wheel locomotive constructed by Robert Stephenson and Co. as an article of regular manufacture weighed 9 tons in working order. The six-wheeled engines which followed weighed 11 1/2 tons. In the course of business locomotives of greater power and greater weight were constructed; and there are locomotives of the present time which weigh 47 1/2 tons in working order, and with the tender full of water and coal about 80 tons gross. There are other engines of special design with twelve wheels in working order, with fuel and water, 72 tons. The contrast is emphasized in the history of the old Garnkirk and Glasgow Railway, which was opened about the year 1829. The first engines of that line weighed from 8 to 9 tons. They had steam-cylinders 11 inches in diameter, and 4-feet wheels of cast-iron, with a working pressure in the boiler of 50 lb per square inch. The "Garnkirk" engine used to take a train of three carriages, together weighing 7 tons gross, at the average speed of 16 miles per hour between Glasgow and Gartsherrie. When the old line, 8 miles in length, was merged in the Caledonian Railway, now comprising a system of nearly 1000 miles in length, the power of the engines was greatly increased, and at this day (1885) there are express passenger engines working over the same ground having large cylinders of 17 or 18 inches in diameter, and wheel of 7 and 8 feet in diameter, weighing from 35 to 45 tons. These engines, with steam of 120 lb pressure per square inch, take a gross load of 90 tons at a speed of from 40 to 50 miles per hour.
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