NZR BB class

NZR BB class
NZR BB class
Power type Steam
Builder A & G Price, Thames, NZ
Serial number 63–92
Build date 1915 (12), 1916 (8), 1917 (8), 1918 (2)
Configuration 4-8-0
UIC classification 2'Dh
Driver diameter 42.5 in (1.080 m)
Length 52 ft 7 12 in (16.04 m)
Weight on drivers 32.5 long tons (33.0 t)
Locomotive weight 43.5 long tons (44.2 t)
Tender weight 25.5 long tons (25.9 t)
Fuel type Coal
Fuel capacity 4 long tons (4.1 t)
Water capacity 1,700 imp gal (7,700 l; 2,000 US gal)
Boiler pressure 175 psi (1.21 MPa)
Firegrate area 16.8 sq ft (1.56 m2)
Heating surface:
724 sq ft (67.3 m2)
Superheater area 208 sq ft (19.3 m2)
Cylinders Two, outside
Cylinder size 17 × 22 in (432 × 559 mm)
Top speed 40 mph (64 km/h)
Tractive effort 20,940 lbf (93.1 kN)
Number in class 30
Number 55, 109, 143, 144, 147, 167, 169, 171, 197, 222, 618–637
Preserved 1 (BB 144)

The BB class of steam locomotives comprised 30 engines operated by New Zealand Railways in the North Island of New Zealand. Similar in design and appearance to the preceding B and BA classes, the first BB class locomotive entered service in February 1915, with the last to commence operations doing so on 8 March 1917. All were built by A & G Price Ltd of Thames, New Zealand, and as their cylinders had a larger diameter than the B and BA locomotives they were capable of generating more power to haul heavier trains. The BB class could haul up to 700 tons of freight on a level railway line, though they were limited to a top speed of around 40 mph.

The BB class did not solely haul freight trains. They were also utilised to haul passenger trains, generally on branch lines where light track meant trains could not be operated at speeds unattainable for the BB class. These trains included services for miners working in coal mines along branches in the Waikato region.

In the later days of steam, powerful locomotives such as the K class were hauling heavy trains that the C class and other shunting locomotives at yards and depots simply could not handle. Accordingly, ten members of the BB class were modified to perform shunting duties and they successfully took on the heaviest of roles.

Most BB locomotives survived into the 1960s. During that decade, the complete withdrawal of the class was undertaken progressively, with the last two, BB 626 and BB 633, formally removed from service in August 1968. Another one of the last to be withdrawn was BB 144 in October 1967, and it survived to be preserved by Mainline Steam, though it is presently inoperable. No other BB locomotive has been preserved.

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