NZR JB class
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||It has been suggested that this article be merged into NZR J class (1939). (Discuss) Proposed since January 2014.|
|NZR JB class|
|Builder||North British Locomotive Works, Glasgow, Scotland|
|Gauge||3 ft 6 in (1,067 mm)|
|Wheel diameter||54 in (1.4 m)|
|Wheelbase||34 ft 10 in (10.6 m)|
|Length||66 ft 11 in (20.4 m)|
|Weight on drivers||44.45 long tons (45.16 t)|
|Locomotive weight||68.55 long tons (69.65 t)|
|Tender weight||40.35 long tons (41.00 t)|
|Locomotive and tender
|108.9 long tons (110.6 t)|
|Fuel capacity||1,350 imp gal (6,100 L)|
|Water capacity||4,000 imp gal (18,000 L)|
|Boiler pressure||200 psi (1,400 kPa)|
|Firegrate area||39.0 square feet (3.6 m2)|
|1,469 square feet (136.5 m2)|
|Superheater area||283 square feet (26.3 m2)|
|Cylinder size||18 in × 26 in (46 cm × 66 cm)|
|Top speed||approx. 72mph|
|Tractive effort||24,960 lbf (111.0 kN)|
|Number in class||12|
|Number||1200, 1203, 1205-06, 1213, 1218, 1224, 1228-30, 1233, 1239|
|Locale||North Island of New Zealand|
|First run||1939 - 1940|
|Last run||1964 - 1967|
|Retired||1964 - 1968|
|Scrapped||1964 - 1968|
|Disposition||Withdrawn; 0 preserved.|
The NZR JB class steam locomotives were all originally members of the J class of 1939. Built by North British Locomotive Works, Scotland, they all initially burned coal and wore distinctive bullet-like streamlining.
Conversion to oil burning
After World War II the railways suffered problematic coal shortages, especially in the North Island. Approval was gained to convert 12 of the J class locomotives into oil-burners, to burn heavy fuel oil which was available in plentiful quantities at the time. The conversion saw the installation of a two-nossle burner in the firebox, removal of the grate and ashpan which was replaced with a firepan lined with bricks, shortening of the superheater tubes in the boiler, removal of the spark arrester in the smokebox, removal of the brick arch, addition of the related controls and gauges for the oil burning equipment, and the tender modified to carry an oil bunker and associated steam piping. Similar to the K and KA Classes which were converted to oil burning at the same time, the JB Class utilized a separate, removable tank which sat in the former coal space. However, the full-width coal bunker of the J-type's Vanderbilt tender was cut down so that the oil tank was visible at the sides, with distinctive vertical supports below. The conversion process generally coincided with the removal of the streamlining, but not always. Once converted, the locomotives were re-classified JB in recognition of the conversion, however they retained their original J class numbers.
The JB Class in service
In service the JB class performed well, but did not distinguish themselves above the unconverted J class nor any of the other J variants. Some of the JB Class received cross-compound Westinghouse pumps in place of the twin single-phase pumps, but others did not. The JB Class only ever saw service in the North Island, as in the South Island coal supplies were plentiful. Some years after conversion to oil, the fuel oil being used became considerably dearer than the coal supplies then being sourced, and there was no longer a coal shortage. However re-conversion back to coal burning did not occur due to objections from the various railway Unions.
Withdrawal and disposal
Some members of the JB Class were among the first of the J 4-8-2 types to be withdrawn, due to the faster wear and tear suffered by the locomotives as a result of oil burning. The last of the class was withdrawn from service by March 1968, by which time steam haulage in the North Island had essentially finished anyway. All of the class were scrapped, although many items from the locomotives were retained as spares for the other J type locomotives still in service in the South Island.
No JB class locomotives were preserved, although the tender from JB 1203 is held by Steam Incorporated. In addition, preserved J class locomotive No. 1236 has been restored as a JB class oil burner by its owners Mainline Steam, although this particular locomotive spent its entire NZR career as a coal-burning J Class. Preserved locomotive J 1211, also owned by Mainline Steam, has been converted to oil burning in the same manner as the JB class, but has not been re-classified to reflect that change.
- Register of New Zealand Steam Locomotives, W.G. Lloyd
- The Locomotives of the Mainline Steam Trust, by Graeme Moffatt