South African Railways 2-10-2 Locomotives in South_Africa


Class Details by Steve Llanso of Sweat House Media

Class 18 (Locobase 2953)

Data from Holland, Volume II (1972); and "Class 18" in South African Railways & Harbours 8 - 1941 Locomotive Diagrams NG supplied in August 2013 by Allen Stanley from his extensive Rail Data Exchange collection. Works numbers were 20787-20788.

Firebox heating surface included 21 sq ft (1.95 sq m) of arch tubes.

Although these engines were indeed very powerful, they proved hard on the track despite the provision of a Krauss-Helmholz truck which combined the leading truck and the leading drive axle. The biggest problem lay in the Gresley conjugated valve gear, which broke frequently. "As a result," says Holland (1972, II),"the engines had to be shopped at under 40,000 miles."


Class 20 (Locobase 2966)

Data from "Class 20" in South African Railways & Harbours 8 - 1941 Locomotive Diagrams NG supplied in August 2013 by Allen Stanley from his extensive Rail Data Exchange collection; and "South African Class 20 2-10-2" in Wikipedia at [], last accessed 3 August 2023.

As might be guessed from its dimensions and weights, the single Class 20 2-10-2 ("Santa Fe" in North American parlance) came to be when A G Watson sought to increase tractive power on South West Africa 40 lb/yard (20 kg/metre) rail. It combined the boiler from a Class 19A 4-8-2 (Locobase 2955), drivers from an 8th class (Locobase 10415), a cylinder dimension similiar to that of the Class 19C engines (Locobase 2958), but with 2" (50.8 mm) shorter stroke, and a specially designed leading bissel truck. Firebox heating surface included 15 sq ft (1.39 sq m) of arch tubes.

Wikipedia offers a succinct comparison with the Garratt Watson dislike so much: "The resulting Class 20 could be considered as Watson's answer to the Class GCA Garratt locomotive which had very similar weight and tractive effort capacities. The Class 20 carried more water and coal than the Garratt and was about 20 long tons (20.3 tonnes) heavier with 33,080 pounds-force (147.1 kilonewtons) tractive effort compared to the 28,470 pounds-force (126.6 kilonewtons) of the Class GCA."

Although traffic in the intended area of operation never demanded such a powerful locomotive, wrote the Wikipedia author, the design itself didn't embarrass: "The Pretoria enginemen considered the Class 20 to be one of their best locomotives since it was free-steaming, more than usually trouble-free and able to handle any load they gave it."

In solo use on several railways, the 20 was converted in 1950 to test the Type CL condensing tender. The concept of recirculating steam as feed water proved quite viable and the SAR put it use in the Class 25 4-8-4s (Locobase 2483).

Its merits well established, the 20 soldiered on until 1961, when it was withdrawn and scrapped.

Principal Dimensions by Steve Llanso of Sweat House Media

Class1820
Locobase ID2953 2966
RailroadSouth African Railways (SAR)South African Railways (SAR)
CountrySouth AfricaSouth Africa
Whyte2-10-22-10-2
Number in Class21
Road Numbers1360-13612485
Gauge3'6"3'6"
Number Built21
BuilderHenschel & SohnSAR
Year19271935
Valve GearWalschaertRC Poppet
Locomotive Length and Weight
Driver Wheelbase (ft / m)21 / 6.4017 / 5.18
Engine Wheelbase (ft / m)38.20 / 11.6432.68 / 9.96
Ratio of driving wheelbase to overall engine wheelbase 0.55 0.52
Overall Wheelbase (engine & tender) (ft / m)67.65 / 20.6259.51 / 18.14
Axle Loading (Maximum Weight per Axle) (lbs / kg)42,560 / 19,30525,760 / 11,685
Weight on Drivers (lbs / kg)207,200 / 93,984128,464 / 58,270
Engine Weight (lbs / kg)256,592 / 116,388159,824 / 72,495
Tender Loaded Weight (lbs / kg)162,680 / 73,790114,352 / 51,869
Total Engine and Tender Weight (lbs / kg)419,272 / 190,178274,176 / 124,364
Tender Water Capacity (gals / ML)6600 / 255100 / 19.32
Tender Fuel Capacity (oil/coal) (gals/tons / Liters/MT)15.40 / 1411 / 41.60
Minimum weight of rail (calculated) (lb/yd / kg/m)69 / 34.5043 / 21.50
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)57 / 144848 / 1219
Boiler Pressure (psi / kPa)215 / 14.80200 / 13.80
High Pressure Cylinders (dia x stroke) (in / mm)21.25" x 28" / 540x711 (3)21" x 24" / 533x610
Tractive Effort (lbs / kg)60,806 / 27581.1737,485 / 17002.93
Factor of Adhesion (Weight on Drivers/Tractive Effort) 3.41 3.43
Heating Ability
Tubes (number - dia) (in / mm)160 - 2.25" / 5784 - 2.25" / 57
Flues (number - dia) (in / mm)34 - 5.5" / 14018 - 5.5" / 140
Flue/Tube length (ft / m)20.59 / 6.2820.03 / 6.11
Firebox Area (sq ft / m2)286 / 26.57140 / 13.01
Grate Area (sq ft / m2)60 / 5.5736 / 3.34
Evaporative Heating Surface (sq ft / m2)3231 / 300.171667 / 154.87
Superheating Surface (sq ft / m2)850 / 78.97415 / 38.55
Combined Heating Surface (sq ft / m2)4081 / 379.142082 / 193.42
Evaporative Heating Surface/Cylinder Volume187.41173.26
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation12,9007200
Same as above plus superheater percentage15,6098640
Same as above but substitute firebox area for grate area74,40333,600
Power L114,58510,148
Power MT775.93870.77

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