صور الصفحة
PDF
النشر الإلكتروني

Locomotive

tion, first suggested by Mr. F. M. Whyte, has been generally adopted by the railways of the United States, and is so simple that but few words will suffice to explain it. A locomotive is designated according to the arrangement and number of its truck wheels, driving wheels and trailing wheels, by numbers; beginning at the forward or pilot end. Thus the locomotive shown in Figs. 3 and 5, called an eightwheel engine, is designated as a 4-4-0, the Atlantic type (Fig. 6) is a 4-4-2, a Consolidation (Fig. 7) a 2-8-0, and so on, the first number

377

4-6-0 Ten-Wheel.
4-6-2 Pacific.
4-8-0 Twelve-Wheel.

Speed. As regards the speed attained by locomotives, it must be conceded that speeds of from 75 to 80 miles per hour were occasionally attained forty or more years ago with very light trains on down grades and on short stretches of track sufficiently straight and well ballasted to permit it; but the accomplishment of modern locomotive engineering has been the production of locomotives that will pull under average conditions of weather,

Locomotive

requirement of present day passenger traffic;, but the running of heavy trains on punctual, regular schedule at a reasonably high speed is demanded. To accomplish this result, as well as to pull the maximum load of freight at moderate rates of speed, the size of locomotives has been increased until two limitations have begun to be felt by designers and builders. One of these is the clearance allowed for outside dimensions by existing tunnels, bridges, and turntables; and the other is the weight that can be safely carried by axle journals

[graphic][subsumed]

F., a mous ign-speed Eight-wheel Locomotive of the New York Central R. R. Rebuilt

indicating the number of truck wheels, the second that of the drivers, and the third the number of trailing wheels. The principal types and their common names are given below:

0-4-0 Four-Wheel Switcher. 0-6-0 Six-Wheel Switcher. 0-8-0 Eight-Wheel Switcher. 2-4-2 Columbia.

2-6-0 Mogul.

2-6-2 Prairie.

2-8-0 Consolidation.

2-8-2 Mikado.

2-10-0 Decapod.

4-4-0 American.

4-4-2 Atlantic.

1906.-No. 1, Table I.

quality of coal, etc., trains weighing from 350 to 500 tons at schedule speeds of 50 to 54 miles per hour, calling for regular running at much higher rates, and occasional bursts of speed as high as 80 miles per hour. A large number of runs have been made in regular service with trains of 250 tons where the speed has reached more than 80 miles per hour, and in some cases more than 90 miles. In two instances velocities of 102 and 112 miles per hour were attained for stretches of from one to three miles. Speed, per se, is not the only

[blocks in formation]
[merged small][merged small][merged small][merged small][merged small][merged small][graphic][subsumed][merged small][merged small][merged small][merged small][merged small][graphic][subsumed][subsumed][merged small][merged small][merged small][merged small]
[merged small][merged small][merged small][merged small][merged small][merged small][graphic][subsumed][subsumed][subsumed][subsumed][subsumed][merged small]

carry the supply. The usual size of tender for passenger and freight traffic is one having a capacity of 6,000 to 9,000 gallons of water and from 10 to 16 tons of coal; and weighing loaded from 70 to 80 tons. The need of this large supply of fuel and water will be better understood when the fact is realized that large locomotives often evap orate 6,000 to 7,000 gallons of water per hour, and consume for this purpose from four to five tons of coal in the same time. The manual effort involved

higher uninterruptedly, until now, 200 lbs. per square inch is standard practice, and a few railways are using, for both simple and compound locomotives, 210 to 225 lbs. These results have been accomplished by the use of better quality steel boiler plate, and by better design and improved systems of bracing and staying boilers. The boilers working at 200 lbs. pressure to-day are less liable to explosion or failure than were those carrying 130 lbs. twenty years ago; and this is due not a little to the more

tion, shown on locomotives in Figs. 4, 8, and 9; but recently another arrangement, commonly used for some time in Europe and known as the Walschaerts valve gear, Figs. 7, 15, and 17, has been applied to American locomotives. The essential point of difference between these gears is the operation of the link, which in the Stephenson gear is moved by two eccentric rods, and suspended by a hanger or lifter from the reverse shaft arm. The valve is reversed by moving the link up or down, and through the medium of the rocker

[graphic][ocr errors][merged small][merged small][merged small]
[graphic][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed]

REPRESENTATIVE MODERN LOCOMOTIVES.

10. British Ten-wheel Passenger Locomotive, North British Locomotive Co. 11. Ten-wheel Passenger, Baldwin Four-cylinder Com pound 12. Santa Fe Type Freight. Four-cylinder, Tandem Compound.-No. 12. Table I. 13. Pacific Type Passenger.-No. 16, Table I. 14. Six-wheel Switching Locomotive-No. 13, Table I.

Locomotive

merely rocks back and forth through a small arc about a fixed centre. In this latter gear, as shown in Fig. 15, the link A is pivoted to a bracket B, secured to the frame or to the guide yoke C, is moved by one eccentric rod D, actuated by a return crank E, on the main crank pin F, and moves the valve G, by means of a bar H, called a radius rod, attached at one end to the valve rod I, and at the other to the block which slides in the link. The reverse shaft arm K, has a lifter L, attached, which raises the radius rod, moving the link block, and thereby moving the valve on its seat. The advantages possessed by the Walschaerts gear are the reduction of the number of pieces and the large decrease of weight as compared with the Stephenson

381

of support on springs and equalizing beams. As may be seen in Fig. 8, a semi-elliptic spring is placed over each driving axle, on each side of the engine, and the two driving springs on either side are joined by an equalizing beam or equalizer, as it is called, a beam supported at its centre on the frame and having its ends connected to the springs in such a manner that any unevenness of the track that would tend to raise or lower any one of the four driving wheels is communicated to the others, and the strain and tendency to twist and distort the frame is distributed and equalized among them all. Locomotives with three or four pairs of drivers have the springs of the forward pair connected with the leading truck by means of a

cross

Locomotive

ator unit taking steam from the boiler. The range of vision of an engine runner is greatly increased by the use of this, but the dazzling quality of the light makes it objectionable in certain localities. Furthermore, to simplify and lighten the work of the engine men, the bell is rung by a pneumatic motor, and the sandbox valve operated by the same kind of power, both these devices drawing air from the air brake reservoir, which is supplied by a steam air-pump whose operation is automatically governed by the pressure of the air pumped, and in such a manner that the air is maintained at the pressure for which the governor is set in accordance with the requirements of the train, i.e. whether freight or high-speed passenger service.

[graphic][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed]

FIG. 15.-Section showing Walschaerts Valve Gear applied to Consolidation Freight Locomotive, American

gear. The motion of the valves thus absorbs less power from the engine, and the parts of the gear, being lighter, are less liable to run hot and wear out.

to

Cast Steel. As locomotives have increased in size and power, it has been found necessary to lighten many parts and strengthen others without unduly increasing their size. For this purpose cast steel has been introduced for locomotives within the last ten years, and has almost entirely superseded cast iron for such parts as pistons, piston rods, crossheads, driving wheels, guide yokes, brackets, etc., and is now used for frames, in this last instance producing a structure at lower cost than a forged iron frame of equal strength. If cast iron were used for the parts of the engine enumerated above. they would have to be made much heavier than those now used made of cast steel, owing to the greater tensile strength and uniformity of structure of the steel.

Spring System.-One of the characteristic features of American locomotives is the method

Locomotive Co.

equalizer, thus giving great flexibility on uneven or crooked track. In the Atlantic and Pacific type engines, the springs of the second and third pair of drivers respectively are equalized with those of the radial trailing truck.

Special Devices.-Any reference to the speed of locomotives would be incomplete without at least a passing reference to the automatic air brake (q.v.). This device, first used about 1871, has made possible the powerful, certain and rapid control of highspeed passenger trains running at regular schedule speeds of almost 70 miles an hour, as well as the safe operation and handling of freight trains three-eighths of a mile in length and weighing 4,000 tons. Standard practice now requires that every wheel on engine and tender be braked, thus gaining the advantage of every ton of weight in reducing the length of a stop. Electric arc lamps have been introduced to a moderate extent for locomotive headlights, the current being supplied by a small turbo-gener

Tractive Power.-The tractive power of a locomotive is calculated from a consideration of the steam pressure, size of cylinders, and diameter of the driving wheels, and is expressed by the formula: d2 X SX.85 p T=

where

T

=

D

Tractive power.

d = diameter of cylinders.
S= stroke of cylinders.
D= diameter of driving wheels.
P= boiler pressure.

This is the maximum tractive effort at slow speeds, say 10 miles per hour. As the speed increases, the action of the valve is such that the average steam pressure throughout the stroke of the piston, called the mean effective pressure, is much less; so that the tractive power falls off rapidly as the speed increases.

Compound Locomotives.-The compound engine, so eminently successful for marine and stationary purposes, has had but limited success when applied to locomotives; but recent improvements in the methods of maru

« السابقةمتابعة »