NZR Q class (1901)

NZR Q class
A NZR Q class locomotive
Type and origin Power type Steam Builder Baldwin Locomotive Works, Philadelphia, USA Serial number 19202–19207 19248–19254 Build date 1901 Total produced 13
Specifications Configuration: ​  • Whyte 4-6-2 Gauge 3 ft 6 in (1,067 mm) Driver dia. 49.1 in (1.247 m) Wheelbase 48 ft 4 in (14.73 m) Length 55 ft 4 in (16.87 m) Adhesive weight 30.7 long tons (31.2 t; 34.4 short tons) Loco weight 48.0 long tons (48.8 t; 53.8 short tons) Tender weight 24.1 long tons (24.5 t; 27.0 short tons) Total weight 72.1 long tons (73.3 t; 80.8 short tons) Fuel type Coal Fuel capacity 5.0 long tons (5.1 t; 5.6 short tons) Water cap 1,700 imp gal (7,700 L; 2,000 US gal) Firebox:  • Firegrate area 40 sq ft (3.7 m2) Boiler pressure 200 psi (1,379 kPa) Heating surface 1,683 sq ft (156.4 m2) Cylinders Two Cylinder size 16 in × 22 in (406 mm × 559 mm) Loco brake Steam Train brakes Air
Performance figures Tractive effort 18,340 lbf (81.6 kN)
Career Number in class 13 Numbers 338-350 Locale Auckland - Rotorua Oamaru - Dunedin First run 1901-12-24 Retired 1957-12-07 Disposition All scrapped

The NZR Q class was an important steam locomotive not only in the history of New Zealand's railway network but also in worldwide railways in general. Designed by New Zealand Government Railways' Chief Mechanical Engineer A. L. Beattie and ordered from the Baldwin Locomotive Works in 1901, they were the first locomotives in the world to be built with the wheel arrangement of 4-6-2. This wheel arrangement came to be known as the Pacific type after the voyage the completed locomotives had to make across the Pacific Ocean to New Zealand. A few instances of the 4-6-2 wheel arrangement are known to have existed prior to 1901, but these were all reconstructions of locomotives that were originally built with a different wheel arrangement, thereby making the thirteen members of the Q class the first "true" Pacifics in the world. The Pacific style went on to become arguably the most famous wheel arrangement in the world.

The Q class's design stems from the requirement for a locomotive similar to the Ub class with the inclusion of a wide firebox to burn poor quality lignite coal from the South Island and the Waikato. Originally plans to equip the new locomotives with a Wootten Firebox would have seen the "Camelback" configuration adopted.

In operation, the locomotives proved to be satisfactory rather than brilliant and they suffered from occasional gear problems. They were soon displaced from the most important and difficult work by members of the A and A^B classes; in fact, later in life, they were re-boilered with A^B boilers. An improved slightly larger 'Q' type was ordered from Baldwins in 1914 but classified A^A due to their dimensions similar to the A class.