NZR UD class

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NZR UD class
Type and origin
Power type Steam
Builder Baldwin Locomotive Works
Build date 1904
Total produced 2
 • Whyte 4-6-0
Gauge 3 ft 6 in (1,067 mm)
Driver dia. 58 in (1,473 mm)
Adhesive weight 29.2 long tons (29.7 t; 32.7 short tons)
Loco weight 39.5 long tons (40.1 t; 44.2 short tons)
Tender weight 27.4 long tons (27.8 t; 30.7 short tons)
Fuel type Coal
Water cap 2,400 imp gal (11,000 l; 2,900 US gal)
Tender cap. 5 long tons (5.1 t; 5.6 short tons)
 • Firegrate area
16.5 sq ft (1.53 m2)
Boiler pressure 185 psi (1,276 kPa)
Heating surface 1,095 sq ft (101.7 m2)
Cylinders 2
Cylinder size 16.5 in × 22 in (419 mm × 559 mm)
Valve gear Stephenson
Performance figures
Tractive effort 15,280 lbf (68.0 kN)
Number in class 2
Retired 1929

The NZR UD class was a class of two 4-6-0 steam locomotives built by the Baldwin Locomotive Works in 1904 for the Wellington and Manawatu Railway Company. When that company was nationalised in 1908, they passed into the ownership of the New Zealand Railways and received the designation UD.


Weighing 39.5 long tons (40.1 t; 44.2 short tons) with a tender of 27.4 long tons (27.8 t; 30.7 short tons), they could haul express trains easily at 50 miles per hour (80 km/h) on mainline railways that were flat or had only a light grade. It had 58 inches (1,473 mm) coupled driving wheels, which were large for the period, a working steam pressure of 185 pounds per square inch (1,276 kPa), and 16.5 inches (419 mm) diameter cylinders with 22 inches (559 mm) piston strokes. The handsome UD locomotives were more than capable of making up lost time, with mile-a-minute runs recalled with pride by Manawatu railway employees.


Although they were fast and powerful, the UD locomotives were unable to survive a programme of standardisation undertaken between 1925 and 1935 to eliminate small locomotive classes that were costly to maintain in favour of large, homogeneous types that provided economies of scale. They were written off in 1929.


  • Cassells, K.R. (1994). Uncommon Carrier: The History of the Wellington and Manawatu Railway Company, 1882-1908. Wellington: NZRLS. pp. 156, 169. ISBN 0-908573-63-4.