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Aa Class
CLASS  Aa    4-6-2

Introduced: 1914 Number in Class: 10

Aa Class Register

Locomotive Specifications

   Baldwin Locomotive Works, Philadelphia, USA.

Engine Weight:    
50.5 tons
Tender Weight:    38.0 tons Total Weight:    88.5 tons Adhesive Weight:    
34.7 tons
Length over Buffers:    
58' 5"
Total Wheelbase:    50' 3" Engine Wheelbase:    27' 3" Coupled Wheelbase:    
10' 0"
Tender Wheelbase:    14' 6" Driver Wheel Dia.:    49" Cylinders HP:    
Two - 18" x 24"
Cylinders LP:    
Grate Area:    28.3 sq ft Evaporative Area:    
1459 sq ft
Superheated Area:    
254 sq ft
Working Pressure:    
170 psig
Tractive Effort:    
21580 lbs f
Coal Capacity:    5.0 tons Oil Capacity:     Water Capacity:    
3500 gals

Remarks:     These new Pacifics were an enlarged and improved version of the 1901 'Q' and were intended for heavy haulage on the North Island Main Trunk line. The capacity of the tender was increased that made longer runs possible. these powerful locomotives gave little trouble in service and were highly regarded. These ten Baldwin built locomotives were rebuilt with 'Ab' boilers and with altered cab and tender.
The 'Aa' class was one of the most successful of the classes ever to work on the NZR.