NZR WF Class - Construction and Design

Construction and Design

In 1902, a drawing was made showing a 2-6-4T tank locomotive, based on a proposal to convert the NZR V class 2-6-2 tender locomotives to tank locomotives. It was noted that the new engine, with a tractive effort of 10,260lbs was considerably less that the 12,890lbs of the slightly smaller NZR W class 2-6-2T, and that a new boiler with a greater working pressure of 140psi would be required to have made the conversion of any real use. It was considered uneconomic to fit new boilers to the old V class frames and running gear, which would have retained the obsolete Stephenson link motion and so the proposal lapsed in favour of developing the last three engines of the WA class 2-6-2T tank locomotives, nos. 50, 68, and 137.

In 1903, chief draftsman G. A. Pearson designed what was to become the eventual WF class tank locomotive. The new locomotive proposed was a modestly-sized 2-6-4T tank locomotive with 45-inch driving wheels and an adhesive weight of just under 27 tons. The Walschaerts valve motion actuated inside-admission piston valves, which would later become a standard on all subsequent NZR designs. With a maximum 9.3 tons axle loading on the driving wheels, the new locomotive would have a wide radius of action. Tractive effort was calculated at 15,330lbs with a working boiler pressure of 200psi.

Forty-one engines of the type were built:

Of the forty-one WF class locomotives built, thirty-nine were built for NZR. The other two were built by A & G Price of Thames for the Public Works Department in 1906, who allocated them numbers PWD 501 and 502. These locomotives were taken over by the NZR in 1909, and were renumbered as WF 467 and WF 468 respectively.