NZR G Class (1928) - Introduction

Introduction

In 1928, New Zealand Government Railways obtained and operated three unusual Garratt locomotives in the 4-6-2 + 2-6-4 layout from Beyer, Peacock and Company of the United Kingdom. These engines had three cylinders (24 inches x 16.5 inches) on each of the two set of engine frames, thus creating a 6-cylinder Garratt. The engines entered service in 1929.

Walschaerts valve gear operated the outside cylinders with the inner third cylinder operated by a Gresley mechanism. The locomotives proved a disaster on the light NZR tracks. W. W. Stewart, in his book When Steam was King (pp. 98-104) suggested the most likely reason was because the engines were too powerful for the system and also the valve gear mechanisms were complicated. Stewart stated, and existing photos verify, that the design was most unusual in that the coal bunker was carried on an extension to the boiler frame rather than the normal Garratt positioning on the rear engine frame.

The engines operating at 200 psi and delivered 51,580 lbs of tractive effort, which on the lightly laid New Zealand tracks, proved to be too powerful for the drawbars on rolling stock, and broken drawbars occurred wherever the engines ran. Further, the locomotives when hauling a full load, generated such intense heat in restricted tunnels, which are common in New Zealand, that crews refused to work them.