Other formats

    TEI XML file   ePub eBook file  

Connect

    mail icontwitter iconBlogspot iconrss icon

The New Zealand Railways Magazine, Volume 7, Issue 1 (May 1, 1932.)

The Tendency in Locomotive Design — Wheel Arrangement in Relation to Modern Development

page 43

The Tendency in Locomotive Design
Wheel Arrangement in Relation to Modern Development
.

In the March-April issue of the New Zealand Railways Magazine, 1931, appeared a brief description and an outline drawing of an interesting locomotive which is to be introduced on our State Railways in the near future.

The choice of such a modern type of high capacity locomotive, with the 4-8-4 wheel arrangement as based upon Whyte's Locomotive Classification System, indicates that our Designing Engineers have adopted the very latest trend of design in the locomotive world.

This new power unit marks the most important development of the orthodox type of steam locomotive designed and built by the Mechanical Engineers of the Department, and in view of the unique constructional features of the locomotive, the following facts concerning the overseas development and progress of machines of similar type, may no doubt be of interest to readers of our Magazine.

It is interesting to note that the locomotive is the first of its kind (carrying a separate tender) to be designed with four wheels under the firebox, i.e., four-wheel trailing truck, for service on New Zealand Railways.

Country of Origin.

The first locomotive to be built with a four wheel truck under the firebox and carrying a separate tender, was placed in service in 1910 by the Northern Railway Company of France. It was given the name of “Baltic” type and had a wheel arrangement of 4-6-4, representing the first real advance over the 4-6-2 “Pacific” type, the latter having a similar wheel arrangement to our A and Ab class locomotives.

Locomotives with the 4-6-4 wheel arrangement were confined to the European Railways until 1927—i.e., for seventeen years after this particular type was originally evolved.

Success in United States.

The first railway locomotive building company outside those of Europe to utilise these machines was the American Locomotive Company of Schnectady, New York. The locomotive referred to was completed and put into service by the New York Central Lines on 14th February, 1927. It was designated the “Hudson” type, the idea of its introduction being that of maintaining with ease the exacting schedules as demanded by the operation of the New York Central's world famous New York-Chicago, 20th Century Limited.

The “Hudson” type represented at the time the greatest advance in high speed locomotive design in the United States, and so definite was its success in actual operation that some hundreds of these locomotives are now in service throughout the New York Central System.

The development of such a locomotive was called for by present-day demands for higher speeds with increased train loads on long sustained runs. It was found, in practice, that the horse-power capacity of a locomotive of the 4-6-2 wheel arrangement was insufficient to meet the conditions of modern traffic, and that a more powerful locomotive was required. As the 4-6-4 type permitted the application of a larger boiler and firebox without any material increase in axle loading and also a lessened percentage of total weight on the drivers, its popularity throughout the United States was assured.

However, with all its efficiency, the ultimate capacity of the 4-6-4 machine proved to be inadequate to meet the special conditions experienced on many lines in the United States. The “Mountain” type, 4-8-2 (similar wheel arrangement to our Class X units) had, up to a point, given satisfactory results, but with the need for further increased boiler capacity an advance was made over the page 44 page 45 “Mountain” type by converting the 4-8-2 into a 4-8-4 type wheel arrangement locomotive. It will be thus appreciated that the 4-8-4 wheel arrangement bears the same relation to the 4-8-2 as the 4-6-4 does to the 4-6-2.

With the exception of certain ten coupled and Mallet Articulated locomotives which are handling traffic over exceptionally difficult territory, it is recognised that the locomotive of the 4-8-4 wheel arrangement represents the highest capacity thus far attained in a steam locomotive.

The Local Units.

In designing a locomotive of the 4-8-4 wheel arrangement for service in New Zealand, our Mechanical Engineering staff have followed, therefore, the most up-to-date practice overseas. Apart from the increased capacity of the new locomotives, their utilisation will result in a very marked improvement in operating efficiency.

The new locomotives are also notable in that provision is made for additional power, if required. This added power will be derived from a trailing truck booster, a further distinct departure in locomotive design so far as New Zealand is concerned. As the name implies, the locomotive booster is, in reality, a subsidiary
Built In The Department's Workshops. (Photo, A. P. Godher.) Class “C” locomotive, 2-6-2, being the ninth of its type turned out in six months from the Hutt Valley Workshops, Wellington, N.Z.

Built In The Department's Workshops.
(Photo, A. P. Godher.)
Class “C” locomotive, 2-6-2, being the ninth of its type turned out in six months from the Hutt Valley Workshops, Wellington, N.Z.

2-cylinder locomotive driving the rear truck of the machine. It is put in or out of operation at the will of the enginedriver, and in most locomotives it becomes inoperative after attaining a speed of fifteen miles per hour.

Many progressive railways abroad have applied boosters to their locomotives. The booster gives the power needed for starting and accelerating trains that the main engine can haul when working at its highest efficiency. It also assists in maintaining a fair speed on heavy grades, and because of its greater flexibility, fits into the present-day scheme of railway operating.

It is recognised that the unused adhesions of trailer or tender trucks have unused boiler capacity also, and with a drive on any of these wheels, greater results in the more prompt and smoother starting and greater uniformity of train speed are gained, as well as a lower tax on the main engine.

The principle of the booster is to make use of idle weight (hitherto unproductive) thus increasing appreciably the working efficiency of the locomotive.

The advance in locomotive wheel arrangement from the 4-6-2 to the 4-8-4 is clearly shown in the illustrations that accompany this article.