| NZR Q class | |
|---|---|
| A NZR Q class locomotive | |
| Power type | Steam |
| Builder | Baldwin Locomotive Works, Philadelphia, USA |
| Serial number | 19202–19207 19248–19254[1] |
| Build date | 1901 |
| Configuration | 4-6-2 |
| Gauge | 3 ft 6 in (1,067 mm) Cape gauge |
| Driver diameter | 49.1 in (1.25 m) |
| Wheelbase | 48 ft 4 in (14.73 m) |
| Length | 55 ft 4 in (16.87 m) |
| Weight on drivers | 30.7 long tons (31.2 t) |
| Locomotive weight | 48.0 long tons (48.8 t) |
| Tender weight | 24.1 long tons (24.5 t) |
| Locomotive & tender combined weight |
72.1 long tons (73.3 t) |
| Fuel type | Coal |
| Fuel capacity | 5.0 long tons (5.1 t) |
| Water capacity | 1,700 imp gal (7,700 L) |
| Boiler pressure | 200 psi (1,400 kPa) |
| Firegrate area | 40 sq ft (3.7 m2) |
| Cylinders | Two |
| Cylinder size | 16 × 22 in (41 × 56 cm) |
| Tractive effort | 18,340 lbf (81.6 kN) |
| Locomotive brakes | Steam |
| Train brakes | Vacuum |
| Number in class | 13 |
| Number | 338-350[1] |
| 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.
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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 AB classes; in fact, later in life, they were re-boilered with AB boilers. An improved slightly larger 'Q' type was ordered from Baldwins in 1914 but classified AA due to their dimensions similar to the A class.
They saw out their final years working in Otago and the West Coast and the last Q class locomotive was retired in 1957. No examples of the class were preserved.
The members of this Q class should not be confused with the members of 1878's Q class. As all of the 1878 locomotives had been withdrawn by 1901, the classification was free to be used again.