New Zealand Government Railways 4-6-4 Locomotives in New_Zealand


Class Details by Steve Llanso of Sweat House Media

Class Wab (Locobase 2490)

Basically a tank-engine variant of the Ab Pacifics, these were used in suburban commuting service in Auckland and Wellington. Some also operated between Taihape and Taumarunui on the North Island. Others were used in short-haul mainline service on the South Island between Dunedin and Oamaru, where the grade could reach 2%. In addition to the large side tanks, the boiler had an extra sand dome for more sanding capacity. As the tank engines were replaced by larger 4-8-2 tender engines, those on the South Island were converted to 4-6-2 Abs.

One preserved engine -- 794 -- racked up 837,400 miles in demanding service before it was retired.

Data from John Garner's comprehensive site at http://www.trainweb.org/nzsteam ... (October 2002).


Class We (Locobase 5189)

Data from John Garner's comprehensive site at http://www.trainweb.org/nzsteam ... (October 2002).

These three tanks were rebuilt from B-class 4-8-0s (Locobase 9568) for helper service over the Rimutaka Incline between Upper Hutt and Cross Creek.


Class Wg (Locobase 5191)

Data from John Garner's comprehensive site at http://www.trainweb.org/nzsteam ... (October 2002). supplemented by diagrams supplied by NZGR's general manager T Ronayne in "Locomotive Building in New Zealand", Railway Engineer, Volume 34, No 5 (May 1913), pp. 183-186.

Handsome follow-ons to the Wfs, all from Hillside. These were slightly larger, but more important, they put more than 6,000 additional pounds on the drivers. Again the size and arrangement proved quite useful and these engines served for years as both commuter locomotives and mail-train engines.


Class Ws (Locobase 5192)

Like the 1917 Wabs, these were also tank-engine variants of the Ab Pacifics, but designed from the outset for suburban service. Note the difference in superheat. The class was later (1932-1933) redesignated Wab and grouped with the others.

Data from John Garner's comprehensive site at http://www.trainweb.org/nzsteam ... (October 2002).


Class Ww (Locobase 5193)

Data from John Garner's comprehensive site at http://www.trainweb.org/nzsteam ... (October 2002).

Essentially superheated Wg engines, these had the usual differences of larger pistons and lower boiler pressure. They served Wellington and Auckland suburban traffic and some main-line and branch-line runs as well. They were rebuilt in the 1950-1960 era with higher-pitched boilers.

Principal Dimensions by Steve Llanso of Sweat House Media
ClassWabWeWgWsWw
Locobase ID2490 5189 5191 5192 5193
RailroadNew Zealand Government RailwaysNew Zealand Government RailwaysNew Zealand Government RailwaysNew Zealand Government RailwaysNew Zealand Government Railways
CountryNew ZealandNew ZealandNew ZealandNew ZealandNew Zealand
Whyte4-6-4T4-6-4T4-6-4T4-6-4T4-6-4T
Number in Class303201351
Road Numbers
Gauge3'6""3'6""3'6""Std3'6""
Number Built16201351
BuilderseveralNZGRNZGRseveralNZGR
Year19171902191019231913
Valve GearWalschaertWalschaertWalschaertWalschaertWalschaert
Locomotive Length and Weight
Driver Wheelbase (ft / m)10 / 3.059 / 2.7410 / 3.0510 / 3.0510 / 3.05
Engine Wheelbase (ft / m)33.09 / 10.0929.09 / 8.8729.62 / 9.0333.09 / 10.0929.62 / 9.03
Ratio of driving wheelbase to overall engine wheebase 0.30 0.31 0.34 0.30 0.34
Overall Wheelbase (engine & tender) (ft / m)33.09 / 10.0929.09 / 8.8729.62 / 9.0333.09 / 10.0929.62 / 9.03
Axle Loading (Maximum Weight per Axle) (lbs / kg)31,360 / 14,225
Weight on Drivers (lbs / kg)94,080 / 42,67478,400 / 35,56266,528 / 30,17782,432 / 37,39166,528 / 30,177
Tender Loaded Weight (lbs / kg)
Total Engine and Tender Weight (lbs / kg)160,160123,648112,000160,160115,360
Tender Water Capacity (gals / ML)2040 / 7.732400 / 9.091680 / 6.362040 / 7.731680 / 6.36
Tender Fuel Capacity (oil/coal) (gals/tons / ML/MT) 3.30 / 3 2.20 / 2 2.20 / 2 3.30 / 3 2.20 / 2
Minimum weight of rail (calculated) (lb/yd / kg/m)52 / 2644 / 2237 / 18.5046 / 2337 / 18.50
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)54 / 137242.50 / 108045 / 114354 / 137245 / 1143
Boiler Pressure (psi / kPa)200 / 13.80180 / 12.40200 / 13.80200 / 13.80180 / 12.40
High Pressure Cylinders (dia x stroke) (in / mm)17" x 26" / 432x66016" x 22" / 406x55914" x 22" / 356x55917" x 26" / 432x66015.5" x 22" / 394x559
Tractive Effort (lbs / kg)23,655 / 10729.7420,275 / 9196.6016,290 / 7389.0323,655 / 10729.7417,971 / 8151.52
Factor of Adhesion (Weight on Drivers/Tractive Effort) 3.98 3.87 4.08 3.48 3.70
Heating Ability
Firebox Area (sq ft / m2)88 / 8.18
Grate Area (sq ft / m2)33 / 3.0717.50 / 1.6316.90 / 1.5733 / 3.0716.90 / 1.57
Evaporative Heating Surface (sq ft / m2)1146 / 106.511037 / 96.38738 / 68.561148 / 106.69526 / 48.88
Superheating Surface (sq ft / m2)277 / 25.74183 / 17.01131 / 12.17
Combined Heating Surface (sq ft / m2)1423 / 132.251037 / 96.38738 / 68.561331 / 123.70657 / 61.05
Evaporative Heating Surface/Cylinder Volume167.78202.55188.28168.07109.48
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation66003150338066003042
Same as above plus superheater percentage78543150338075243650
Same as above but substitute firebox area for grate area17,600
Power L14508
Power MT448.16

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