South African Class 12A 4-8-2 Explained

South African Class 12A & 12AR 4-8-2
Hatnote:♠ Class 12A as built with a Belpaire firebox
Class 12AR rebuilt with a round-topped firebox
Type MP1 tender - Type MT tender
Powertype:Steam
Designer:South African Railways
(D.A. Hendrie)
Builder:North British Locomotive Company
Henschel and Son
Serialnumber:NBL 21738-21757, 22751-22765, 23891-23903
Henschel 21046-21051, 21428-21440
Buildmodel:Class 12A
Builddate:1919-1929
Totalproduction:75
Whytetype:4-8-2 (Mountain)
Uicclass:2'D1'h2
Driver:2nd coupled axle
Leadingdiameter:NaN0NaN0
Coupleddiameter:510NaN0
Trailingdiameter:330NaN0
Tenderdiameter:340NaN0
Wheelbase: 58feet
61feet
Engine Total:32feet
Leading:6feet
Coupled:13feet
Tender Total: 16feet
20feet
Tenderbogie: 4feet
6feet
Over Couplers: 66feet
69feet
Height:♠ 12feet
130NaN0
Frametype:Plate
Axleload:♠ 17lt
17lt
Leadingbogie/Pony:♠ 17lt
17lt
Coupled 1:♠ 17lt
17sigfig=4NaNsigfig=4
Coupled 2:♠ 17lt
17lt
Coupled 3:♠ 17lt
17lt
Coupled 4:♠ 17lt
17lt
Trail Bogie/Pony:♠ 12lt
Tenderbogieload:Bogie 1:
27lt
32lt
Bogie 2:
23lt
33lt
Tenderaxle: 13lt
16lt
Weightondrivers:♠ 69lt
68lt
Locoweight:♠ 99lt
99lt
Tenderweight: 51lt
66sigfig=4NaNsigfig=4
Locotenderweight:♠ 150lt
150lt
♠ 165lt
165lt
Tendertype: MP1 (2-axle bogies)
MT (2-axle bogies)
MP, MP1, MR, MS, MT, MT1, MT2, MX, MY, MY1 permitted
Fueltype:Coal
Fuelcap: 101NaN1
121NaN1
Watercap: 4250sigfig=3NaNsigfig=3
6000sigfig=3NaNsigfig=3
Fireboxtype:♠ Belpaire - Round-top
Firearea:♠ 40.5square feet
41square feet
Pitch:♠ 7feet
8feet
Diameterinside:♠ 5feet
60NaN0
Lengthinside:♠ 180NaN0
19feet
Smalltubediameter:♠ 159: NaN0NaN0
119: NaN0NaN0
Largetubediameter:♠ 24 NaN0NaN0
30: NaN0NaN0
Boilerpressure:♠ 1900NaN0
Safetyvalvetype:♠ Ramsbottom - Ross Pop
Totalsurface:♠ 2510square feet
2502square feet
Tubearea:♠ 2301square feet
2338square feet
Fireboxarea:♠ 209square feet
164square feet
Superheaterarea:♠ 466square feet
480square feet
Cylindercount:Two
Cylindersize:240NaN0 bore
260NaN0 stroke
Valvegear:Walschaerts
Valvetype:Piston
Coupling:Johnston link-and-pin
AAR knuckle (1930s)
Tractiveeffort:♠ 41840lbf @ 75%
Operator:South African Railways
Operatorclass:Class 12A & 12AR
Numinclass:SAR 67, Industrial 8
Fleetnumbers:1520-1550, 2103-2138
Deliverydate:1919-1929
Firstrundate:1919
Withdrawndate:1980s
Notes:The leading coupled axle had flangeless wheels

The South African Railways Class 12A 4-8-2 of 1919 was a steam locomotive.

Between 1919 and 1929, the South African Railways placed 67 steam locomotives with a 4-8-2 Mountain type wheel arrangement in service. Between 1947 and 1953, eight were also built for industrial use.[1]

Manufacturers

The Class 12A was the final locomotive design by D.A. Hendrie, Chief Mechanical Engineer (CME) of the South African Railways (SAR) from 1910 to 1922, and one of his finest. It was an improved and larger version of his Class 12 locomotive, with larger diameter cylinders to increase tractive effort and a redesigned boiler.[1]

Between 1919 and 1929, altogether 67 of them were built on five orders, 48 by the North British Locomotive Company (NBL) in Scotland and 19 by Henschel and Son in Kassel, Germany.[1]

Characteristics

At the time, these locomotives were of the maximum size permissible for the Mountain type on Cape gauge. They were designed primarily to supplement the Class 12 locomotives which were already working on the coal line between Witbank and Germiston. Since these engines had a slightly heavier axle load than the predecessor Class 12, it was foreseen that they would be able to take a slightly increased load on the Witbank-Germiston section.[1] [3]

The locomotives were built on NaNinches plate frames. They were superheated and had piston valves, Walschaerts valve gear and Belpaire fireboxes which included combustion chambers. The boilers of the first two batches of 1919 and 1921 were equipped with Ramsbottom safety valves, while works pictures of the remainder show that they were equipped with Ross pop safety valves. The feedwater supply of the third and subsequent batches was by a top feed arrangement through copper pipes which were run from the running boards on each side to the top of the boiler ahead of the steam dome.[1]

The original Class 12A superheater header was arranged with the Gresley type air valve which was introduced to prevent the risk of superheater elements being burned or damaged by overheating while engines were drifting. The valve automatically opened when the regulator was closed and allowed outside air to be drawn into the superheater elements. Even though experience showed that the heated air which then entered the steam chests and cylinders was harmful to cylinder lubrication with no apparent effect on the life of the superheater elements, it was some years before the use of these air valves was finally discontinued.[1]

The first two batches, delivered in 1919 and 1921, were equipped with the Johnston link-and-pin couplers which had been in use since the establishment of the Cape Government Railways in 1873. By the time the third batch arrived in 1928, the SAR had begun to convert its Cape Gauge rolling stock to AAR knuckle couplers. The third to fifth batches were therefore delivered with the new coupling system.[5] [6]

Tenders

The locomotives were delivered new with two tender types, the Types MP1 and MT. While sources are unclear about which batches of the Class 12A were delivered with which tender type, builder's works photographs show the NBL-built locomotives of 1919 and 1921 with Type MP1 tenders, and the Henschel-built and subsequent NBL-built locomotives with Type MT tenders.[1] [5] [6]

Type MP1 tender

On the Type MP1 tender, the top of its coal bunker sides were distinctly separate, mounted within the top edging of the water tank. It had a fuel capacity of 101NaN1 and a water capacity of 4250sigfig=3NaNsigfig=3, with a 13lt axle load.[5] [6]

Many of these tenders were subsequently rebuilt to smooth-sided Type MR tenders with a 4600sigfig=3NaNsigfig=3 water capacity and a 13lt axle load.[5] [6]

Type MT tender

The heavier Type MT tender had smooth sides all the way to the top of the coal bunker. It had a fuel capacity of 121NaN1 and a water capacity of 6000sigfig=3NaNsigfig=3, with a 16lt axle load.[5] [6]

Reboilering

During the 1930s, many serving locomotives were reboilered with a standard boiler type designed by then CME A.G. Watson as part of his standardisation policy. In the process, they were then also equipped with Watson cabs with their distinctive slanted fronts, compared to the conventional vertical fronts of the original cabs. Such Watson Standard reboilered locomotives were reclassified by adding an "R" suffix to their classification.[5] [6]

When Class 12A locomotives numbers 1540 and 2135 became the first to be reboilered in 1943, however, none of the Watson Standard boilers were deemed suitable since the Watson Standard no. 2 series were too small, while the no. 3 series were too large. A special boiler was therefore designed for them by Dr. M.M. Loubser, the CME at the time. These boilers did not conform to any of the Watson Standard boilers and were a totally new type of rather massive proportions which, on a locomotive with relatively small coupled wheels, created an impression of great power. Certain features common to the Watson Standard boilers were incorporated in the design, however, since it was deemed necessary to have the greatest possible degree of interchangeability of parts with those of the Watson Standard boilers. The boiler size was between that of the Watson Standard numbers 2 and 3 boilers.[1] [7]

Unlike the original Class 12A boilers, initial and in-service repair cost considerations led to the Loubser boiler being built without a combustion chamber. The round-top firebox was radially stayed and the first two rows of stays were flexible. Similar stays were fitted in the side, back and throat plates and in the breaking zones. There were eight cross stays over the top of the firebox, which was of steel.[1]

The original Belpaire boilers were fitted with Ramsbottom safety valves while, like the Watson Standard boilers, the Loubser boiler was fitted with two NaN0NaN0 Ross pop safety valves. Feedwater was supplied by two Davies and Metcalf injectors through a top-feed arrangement. At the firebox, the boiler was carried by a vertical transverse plate at the back and at the two front corners by sliding grease-lubricated shoes which rested on gunmetal liner plates which, in turn, were fixed to specially-designed steel brackets welded to the inside of the bridle casting. The boiler barrel was attached to the engine frame by four diaphragm plates, bolted to "T" sections which were riveted to the barrel.[1]

Altogether 44 Class 12A locomotives were eventually reboilered with Loubser boilers and reclassified to Class 12AR. During the reboilering, which included the installation of Watson cabs, the locomotives were also equipped with a longer smokebox which resulted in the distinctive appearance of the Class 12AR. Like the Watson Standard boilers, the Loubser boilers also had the distinctive rectangular regulator cover just to the rear of the chimney. In the case of the Classes 12A and 12AR locomotives, three even more obvious differences are the extended smokebox, the Watson cab and the absence of the Belpaire firebox hump between the cab and boiler on the reboilered locomotives.[5] [6]

The reboilered locomotives were considered by some enginemen to be inferior steamers compared to the as-built engines. A shortened version of Loubser's Class 12AR boiler was later used on the new Class S1 shunting locomotives.

Service

South African Railways

When new, the Class 12A locomotives were placed in service hauling coal on the section from Witbank to Germiston. The unreboilered locomotives spent a large part of their working lives in Transvaal, mainly in Western Transvaal and shedded at Springs and Germiston, a few in Eastern Transvaal and shedded at Nelspruit and Waterval Boven, and one at De Aar in the Cape Province. The class also served in Natal during the late 1920s, probably after the arrival in numbers of the Class 15CA in 1929. Here they were worth two more coaches than a Class 14 on the 1921 mainline between Durban and Pietermaritzburg. A Class 12A locomotive was in charge of the last steam-hauled mainline passenger train to depart from Durban station after electric traction reached Durban from Pietermaritzburg during 1936. In 1977, all the remaining Class 12A locomotives were relocated to the Cape Northern system for shunting at De Aar and at Beaconsfield in Kimberley.[3] [8]

The more numerous reboilered Class 12AR locomotives worked throughout most parts of South Africa, being shedded at Kimberley, De Aar, Port Elizabeth and East London in the Cape Province, Glencoe and Newcastle in Natal, Klerksdorp in Transvaal and Kroonstad in the Orange Free State. East London and Port Elizabeth each received four, the latter being allocated engine numbers 1544, 1545, 2125 and 2129 for use on the fast Saturday morning passenger trains to Cape Town.

The Classes 12A and 12AR versions both proved to be very successful engines which performed well, with low repair costs. Modifications in design of details after entering service were negligible.[1]

Industrial service

None of the SAR Class 12A or Class 12AR locomotives were sold into industrial service, but between 1947 and 1953 eight Class 12A locomotives, similar to the unreboilered SAR locomotives but without superheaters, were built new for industrial service by NBL.

Works numbers

The builders, years built, works numbers, reboilering particulars and original tender types are listed in the table.[5] [6]

Preservation

Class Number Works nmr THF / Private Leaselend / Owner Current Location Outside South Africa ?
12R 1865 BP 5994 Private Kimberley Locomotive Depot
12R 1947 BALDWIN 52754 THF Reefsteamers Germiston Locomotive Depot
12R 1505 NBL 20176 THF Umgeni Steam Railway Kloofstation (Inchaga)
12R 1510 NBL 20812 Private Creighton Station
12A 2111 NBL 22751 THF Bloemfontein Locomotive Depot
12AR 1535 NBL 21753 THF Reefsteamers Germiston Locomotive Depot

Notes and References

  1. Espitalier, T.J.; Day, W.A.J. (1945). The Locomotive in South Africa - A Brief History of Railway Development. Chapter VII - South African Railways (Continued). South African Railways and Harbours Magazine, October 1945. pp. 779-783.
  2. North British Locomotive Company works list, compiled by Austrian locomotive historian Bernhard Schmeiser
  3. https://sites.google.com/site/soulorailway/home/system-7-1/soul-of-a-railway-part-21-witbank-line-by-les-pivnic-eugene-armer-peter-stow-and-peter-micenko Soul of A Railway, System 7, Western Transvaal, based in Johannesburg, Part 21: Witbank Line by Les Pivnic, Eugene Armer, Peter Stow and Peter Micenko. Captions 4-5.
  4. Henschel-Lieferliste (Henschel & Son works list), compiled by Dietmar Stresow
  5. South African Railways & Harbours/Suid Afrikaanse Spoorweë en Hawens (15 Aug 1941). Locomotive Diagram Book/Lokomotiefdiagramboek, 3'6" Gauge/Spoorwydte. SAR/SAS Mechanical Department/Werktuigkundige Dept. Drawing Office/Tekenkantoor, Pretoria. pp. 43-44.
  6. South African Railways & Harbours/Suid Afrikaanse Spoorweë en Hawens (15 Aug 1941). Locomotive Diagram Book/Lokomotiefdiagramboek, 2'0" & 3'6" Gauge/Spoorwydte, Steam Locomotives/Stoomlokomotiewe. SAR/SAS Mechanical Department/Werktuigkundige Dept. Drawing Office/Tekenkantoor, Pretoria. pp. 6a-7a, 41, 43, 45.
  7. Espitalier, T.J.; Day, W.A.J. (1946). The Locomotive in South Africa - A Brief History of Railway Development. Chapter VII - South African Railways (Continued). South African Railways and Harbours Magazine, Jul 1946. p. 542.
  8. https://sites.google.com/site/soulorailway/home/system-6-1/system-6 Soul of A Railway, System 6, Part 1: Durban Old Station. Captions 12-13.

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