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.

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.