The New Zealand Railways Magazine, Volume 9, Issue 7 (October 1, 1934)
Locomotive Developement. — in — New Zealand — The “Pacific” Type. its Genesis and Triumph.
The “Pacific” Type. its Genesis and Triumph.
By the year 1900, experience with the “U” and “B” class of locomotives had made manifest the fact that the New Zealand locomotive designer was per se quite as competent as his competitor overseas; that his better knowledge of local conditions enabled him to design machines better adapted for the needs of the railway service, and that, with this initial advantage, the local railway workshops could build locomotives which, in the final analysis were more economical than the imported machines.
At this time, too, the policy of the Government of the day was strongly in favour of having, where possible, all work done in New Zealand. The Railway Department naturally, therefore, adopted the policy that in future all new locomotives required should be designed and built in New Zealand. And by the irony of fate immediately followed the largest importation of English and American locomotives that the railways had yet known!
The reasons for this anomaly were obvious enough. The colony was at this time just recovering from the severest and (let us hope) the longest “depression” that it has ever known.
This depression quickly reached its apex in 1888, but it was a long ten years after before the cloud lifted finally. During these years the provision of new locomotives was out of the question. By 1900 prosperity and progress had quite suddenly returned, and greatly increased traffic came to the railways. The new traffic called for heavier, faster, and more frequent trains. The locomotive equipment, after ten years' stagnation, was of course quite unequal to the demands of the new conditions; and, while the Addington workshops had proved that good locomotives could be built in New Zealand, and that the shops were able to cope with the normal requirements, the Railway workshops were unable to supply the large number of engines then so urgently needed.
“Cortez silent on a peak in Darien” had nothing on the Baldwin Locomotive Company when it first viewed this sketch. Such a simple solution was seized avidly by the Company, and almost before the first locomotive of the new type could be shipped to New Zealand, Baldwin's were building similar engines for all the American roads. It represents, indeed, a veritable “milestone” in locomotive progress. Engines with six driving wheels and a trailing bogie are, from the mechanical point of view, the most economical form of locomotive. They admit, as one with fewer driving wheels will not admit, the use of a sufficiently large boiler to enable power to be generated with higher efficiency from relatively inferior coals, and their adhesive weight is sufficiently adequate to allow for the traction of trains heavy enough for all but the few most exacting services. They also give such balance between power and weight as to arrive at the lowest possible ratio between these factors, and escape the large increase in friction and wear that is inseparable from the use of more coupled wheels; and, altogether, again from the strictly mechanical point of view, they reach the acme of locomotive attainment, combining power, speed, lightness, symmetry, simplicity and beauty, in a degree not possible with any other type.
The title “Pacific” was given to this outstanding type in recognition of the fact that a New Zealand designer had first proposed it and was entitled to the credit for its introduction.
The great majority of the locomotives built in or for New Zealand during the last thirty-three years have naturally been of the “Pacific” type. The experiment, about 1905, with compound locomotives, lead to the “A” class and the adoption of superheat led, in 1914, to the building of the “Ab” class. This locomotive is a simple superheated engine of the “Pacific” type with a cylindrical tender. Designed under the instructions of Mr. H. H. Jackson (then Chief Mechanical Engineer) it embodied all the best features that New Zealand experience or design had evolved, and is probably the most efficient locomotive ever built for all-round service in the world.
Although seventy-five of these engines had perforce to be built in England as a result of dislocation due to the War, they were all built entirely to New Zealand drawings and specifications. New Zealand track conditions demand that the maximum routine in train speed must not exceed 55 miles per hour, but the “Ab” locomotive can reach seventy miles per hour with safety on a level track; it has developed one horse power for each 100lb. of locomotive weight, which is certainly a record for a moderate sized engine; its fuel efficiency is extraordinarily high and, although this may have been exceeded by special service locomotives, is probably a record for all-round service; it can handle passenger, goods and work trains with equal facility; and the repair costs are markedly low.page break