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From the classification table given, it is apparent that there are a great many different types of locomotives in service. Only the more commonly used types will be discussed, which are as follows: 040, 060, 080, 260, 280, 440, 442, 460, and 462. The types 040, 060, and 080 are largely used for switching service. The 040 type is of the smallest proportions and weights, being found in small yards where only light work is required. The call for heavy duty was met by the 060 type. The fact that the 060 type, being much heavier, has a greater tractive effort and a correspondingly larger steaming capacity, has caused them to be used very extensively. The following figures will aid in giving an idea of their size and capacity:

Weight on drivers (pounds). .... ............................145,000 to 170,000
Diameter of cylinders (inches). ......................................19 to 22
Stroke of piston (inches). ..............................................24 to 26
Diameter of driving wheels (inches). ..............................50 to 56
Working steam pressure (pounds per square inch)........180 to 200

The demand for power, steadily increasing beyond that which could be secured by locomotives of the 060 type, created a new design known as the 8-wheel, or 080 type. This type is used in switching and pushing service and has about 171,000 pounds weight on drivers, cylinders 21 inches in diameter, stroke 28 inches, drivers 51 inches in diameter, and carries 175 to 200 pounds steam pressure. The switching engines of the 060 and 080 type were converted into highclass freight engines by adding two wheel trucks to each, thus developing the 260, or Mogul, and the 280, or Consolidation types.

The Mogul was primarily intended for freight service only, but it is sometimes used in heavy passenger service. The object of the design was to obtain greater tractive force on driving wheels than is possible to obtain with four drivers, as in the 440 type. Fig. 10 illustrates a modern 260, or Mogul type, giving its principal dimensions. This type was more generally used than any other before the increasing requirements of heavy freight service resulted in the development of the 280, or Consolidation type. It is profitable from the standpoint of economy in repairs in selecting the type of locomotive for any service, to use the minimum number of drive wheels possible within the limits of the necessary tractive power, although for freight service involving the handling of heavy trains on steep grades, the 280, or Consolidation type, is required. Where the requirements are not too severe, however, there is a large field for the Mogul type in freight service. Where a large axle load is permitted, the Mogul type may give sufficient hauling capacity to meet ordinary requirements in freight service on comparatively level roads. While not generally recommended for what may be called fast freight service, the 280, or Consolidation type, is sometimes used. Many Mogul locomotives are successfully handling such trains.

The 260 type provides a two-wheel leading truck with good guiding qualities and places a large percentage of the total weight on the driving wheels. A large number of locomotives of this type show an average of 87½ per cent of the total weight of the locomotive on the drivers. Boilers with sufficient capacity for moderate speed may be provided in this type; and with relatively small diameters of driving wheels, it will lend itself readily to wide variations in grates and fireboxes.

The Consolidation locomotive, or 280 type, shown in Fig. 11, was designed, as has been mentioned, for hauling heavy trains over steep grades. It is perhaps more generally used as a high class freight engine than any other type so far developed. Locomotives of this type have been designed and built with total weights varying between 150,000 to 300,000 pounds.

The four most prominent types of passenger locomotives, namely, 440, 442, 460, and 462, have each been developed at different times and in successive order to meet the ever-increasing and changing demands. The 8-wheel or 440 type, commonly known as the American type, was for some time the favorite passenger locomotive, but as the demands for meeting the conditions of modern fast passenger service increased, a locomotive of new design was required. The conditions which were to be met were sustained high speed and regular service. This did not mean bursts of high speed under favorable conditions with a light train running as an extra or special with clear orders, but it meant rather the more exacting requirements of regular service.

Where regular train service had to be sustained day after day at a schedule of 50 miles per hour, it required reserve power to meet the unfavorable conditions of the weather and for an occasional extra car in the train. For such exacting demands, much steam is required and ample heating and grate surface must be provided. In the 440 type with a 4-wheel leading truck and four driving wheels without a trailing truck, the boiler capacity is limited. Not only is the heating surface also limited but the grate area as well, because the grates must be placed between the driving wheels. The desirability of larger boilers and wider grates than the distance between the wheels in the 440 type will permit, led to a ready acceptance of the 442, or Atlantic type locomotive, as shown in Fig. 12. The 442 type combines a 4-wheel leading truck, providing good guiding qualities, and four coupled driving wheels having a starting capacity sufficient for trains of moderate weight, and a trailing truck. The use of the trailing truck permits the extension of the grates beyond the driving wheels thus obtaining a much larger grate area. This wheel arrangement also permits the use of a deep as well as a wide fire-box which is especially advantageous in the burning of bituminous coal. It also gives a much greater depth at the front or throat of the fire-box, which is very important.

As modern passenger service increased and heavier trains had to be drawn, four driving wheels would not give sufficient starting power. Because of the heating surface and grate area being limited by the same factors as mentioned in the 440 type, another type, the 462, or Pacific type, came into favor. As this type was called upon to pull the heaviest passenger trains, much power was required even under very favorable conditions. For such trains, a locomotive having a combination of large cylinders, heavy tractive weight, and large boiler capacity is required. The Pacific type meets these requirements in a very successful way. From a study of Fig. 13, which illustrates such a locomotive, it is obvious that the 462 type differs from the general design of the Atlantic type only in the addition of another pair of driving wheels. This, however, makes possible a much heavier boiler; therefore, more heating surface, more grate area, and greater tractive weight are obtained. Grate areas of from 40 to 50 square feet are possible in this type which provides for the large fuel consumption that is required for the rather severe service. The heating surface is of equal importance since large cylinders require large steaming capacity. The 462 type meets this need also. A comparison of passenger locomotives shows that the Pacific type has more heating surface for a given total weight than is found in any other type of passenger locomotive.

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