South African Class Experimental 1 4-6-2

The South African Railways Class Experimental 1 4-6-2 of 1907 was a steam locomotive from the pre-Union era in the Cape of Good Hope.

In 1907, the Cape Government Railways placed a single experimental three-cylinder compound steam locomotive with a 4-6-2 Pacific type wheel arrangement in service between Beaufort West and De Aar. It was based on the second series of its Karoo Class locomotives. In 1912, when the locomotive was assimilated into the South African Railways, it was renumbered and designated Class Experimental 1.^[1][2][3][4]

Manufacturer

H.M. Beatty

In the first few years of the twentieth century, H.M. Beatty, Chief Locomotive Superintendent of the Cape Government Railways (CGR), experimented with various forms of compound steam locomotives. One of these engines was delivered by the North British Locomotive Company (NBL) in 1907. It was a three-cylinder compound locomotive, based on the second version of the CGR’s Karoo Class. The locomotive was numbered 900, but it was not classified by the CGR and was simply referred to as the Compound Karoo.^[1][2][3][5]

Compound expansion

Compound locomotive

In a compound locomotive, steam is expanded in phases. After being expanded in a high-pressure cylinder and having then lost pressure and given up part of its heat, it is exhausted into a larger-volume low-pressure cylinder for secondary expansion, after which it is exhausted through the smokebox. By comparison, in the more usual arrangement of simple expansion (simplex), steam is expanded just once in any one cylinder before being exhausted through the smokebox.^[6]

Three-cylinder compound

On the Compound Karoo, the cylinders were arranged in the "Smith" system of compounding, with a single high-pressure cylinder situated between the two low-pressure cylinders. The Smith system of compounding was developed from the two-cylinder Worsdell-von Borries compound system. Walter Mackersie Smith, a Scottish engineer, improved on this system by developing a three-cylinder compound system with one high-pressure cylinder inside and two low-pressure cylinders outside. It permitted the locomotive to be worked in either compound, semi-compound or simplex mode.^[1][2][3][7]

Compound mode

When working compound, the whole of the exhaust steam from the high-pressure cylinder passed into the low-pressure cylinders.^[2]

Semi-compound mode

Upon starting, semi-compound working allowed boiler steam to be admitted directly to the low-pressure cylinders through a reducing valve, to obtain greater tractive effort and to avoid starting trouble due to the high-pressure crank being at or near dead centre.^[2]

Simplex mode

Non-return valves were fitted which, under certain conditions, caused both ends of the high-pressure cylinder to be in communication, with the result that the piston would be floating and the low-pressure cylinders would be receiving high-pressure steam, thus converting the engine to simplex working.^[2]

Characteristics

The locomotive had a bar frame, Walschaerts valve gear and used saturated steam.^[3]

The inside high-pressure cylinder had a slide valve below, while the two outside low-pressure cylinders had balanced slide valves above. The cylinder ratio was 1 to 2.45. The outside cranks were placed 90 degrees apart, while the middle inside crank was placed at 135 degrees from each of the outer two. All three cylinders actuated the middle coupled axle and their valves were actuated by three sets of eccentrics on this axle. The exhaust from the high-pressure cylinder passed directly into a large steam chest, common to both low-pressure cylinders, which eliminated the need for a receiver pipe.^[2][3]

Performance

During 1907, extensive comparative tests were carried out with the Compound Karoo and a simplex two-cylinder locomotive, Karoo Class no. 907. Initial results showed that, while the compound locomotive displayed no marked economy of fuel over the simplex, it ran with remarkable steadiness and could take a heavy train up a long continuous grade at a much higher rate of speed than the simplex. With the direct admission of boiler steam into the low-pressure cylinders in semi-compound mode, the engine started without difficulty, without fail.^[1][2]

After having been in service for two years, however, experienced drivers of the Compound Karoo reported that, if treated and handled properly, the compound locomotive could outperform the simplex in terms of power as well as fuel and water consumption. In 1909, Beatty could report that the engine showed a coal economy of 8% in comparison with the simplex, doing the same work. One driver described how the judicious use of semi-compound mode on heavy grades, injecting high-pressure steam in the low-pressure cylinders, enhanced the locomotive’s performance, and how the life of the high-pressure big-end bearings, which initially proved troublesome, could be prolonged by mixing castor oil in with the regular oil which was used on all the bearings and the valve motion.^[1][2]

The long gradients in the Karoo did not allow the locomotive to be worked in simplex mode for extended periods, however, since the boiler's steaming capacity was insufficient. The difficulties regarding accessibility to the inside cylinder, inherent with the cramped space allowed for a third cylinder by the 3 feet 6 inches (1,067 millimetres) Cape gauge, probably also served as a deterrent and only the one locomotive was therefore built.^[2]

Service

Cape Government Railways

The Compound Karoo was placed in service in the Karoo, on the section between Beaufort West and De Aar. It performed well, provided the centre high-pressure big-end bearings were given adequate care and frequent lubrication.^[3]

South African Railways

When the Union of South Africa was established on 31 May 1910, the three Colonial government railways (CGR, Natal Government Railways and Central South African Railways) were united under a single administration to control and administer the railways, ports and harbours of the Union. Although the South African Railways and Harbours came into existence in 1910, the actual classification and renumbering of all the rolling stock of the three constituent railways required careful planning and was only implemented with effect from 1 January 1912.^[4][8]

In 1912, the Compound Karoo was designated Class Experimental 1 on the South African Railways and renumbered 764. It continued to work passenger trains through the Karoo, until it was withdrawn from service in 1933 and scrapped.^[2][3][4][9]

References

Wikimedia Commons has media related to South African Class Exp 1 (4-6-2).

Locomotives of the Cape of Good Hope
7' ¼" gauge	East London 0-4-0VB Table Bay 0-4-0ST Table Bay 0-4-0T Table Bay 0-4-0WT
4' 8½" gauge	Cape 0-4-0T Cape 0-4-2 Cape 2-4-0T CGR 0-4-0ST Aid
3' 6" gauge	CGR 0-4-0ST 1873 CGR 0-4-0ST 1874 CGR 0-4-0ST 1881 CGR 0-4-0ST 1881 Coffee Pot CGR 0-6-0ST CGR 0-6-0T CGR 2-6-0ST 1900 CGR 2-6-0ST 1902 CGR 1st Class 0-4-0ST 1875 CGR 1st Class 0-4-0ST 1876 CGR 1st Class 2-6-0 1876 BP CGR 1st Class 2-6-0 1876 Kitson CGR 1st Class 2-6-0 1879 CGR 1st Class 2-6-0 1891 CGR 1st Class 2-6-0ST CGR 1st Class 4-4-0 CGR 1st Class 4-4-0T CGR 1st Class 4-4-0TT CGR 2nd Class 2-6-2TT CGR 2nd Class 4-4-0T CGR 3rd Class 2-6-0T CGR 3rd Class 4-4-0 1883 CGR 3rd Class 4-4-0 1884 CGR 3rd Class 4-4-0 1889 CGR 3rd Class 4-4-0 1898 CGR 3rd Class 4-4-0 1901 CGR 3rd Class 4-4-0 1903 CGR 4th Class 4-4-2 CGR 4th Class 4-6-0TT 1880 CGR 4th Class 4-6-0TT 1882 CGR 4th Class 4-6-0TT 1882 Joy CGR 4th Class 4-6-0TT 1884 CGR 5th Class 1890 CGR 5th Class 1891 CGR 6th Class 1893 CGR 6th Class 1896 CGR 6th Class 1897 CGR 6th Class 1898 CGR 6th Class 1900 CGR 6th Class 1901 Baldwin CGR 6th Class 1901 Schenectady CGR 6th Class 1901 Neilson's CGR 6th Class 1902 CGR 6th Class 1904 CGR 6th Class 2-6-2 CGR 6th Class 2-6-4 CGR 7th Class 1892 CGR 7th Class 1896 CGR 7th Class 1902 CGR 8th Class 1901 CGR 8th Class 1902 CGR 8th Class 2-8-0 1903 CGR 8th Class 4-8-0 1903 CGR 8th Class 4-8-0 1903 Exp CGR 8th Class 2-8-0 1904 CGR 8th Class 4-8-0 1904 CGR 9th Class 1903 CGR 9th Class 1906 CGR 10th Class CGR Fairlie CGR Karoo 1903 CGR Karoo 1904 CGR Karoo Compound CGR Kitson-Meyer CGR Mountain 4-8-2 CGR Railmotor CGR Tandem Compound 1902 CGR Tandem Compound 1903 Kowie Railway 0-6-0T Kowie Railway 4-4-0T Metropolitan & Suburban 4-6-2T NCCR 7th Class 1899 NCCR 7th Class 1913 Port Elizabeth 0-4-0ST
2' 6" gauge	Cape Copper 0-6-0T Cape Copper Britannia Cape Copper Caledonia Cape Copper Clara Cape Copper Condenser Cape Copper Scotia Namaqua Copper Pioneer Walvis Bay Hope
2' gauge	CGR Baldwin 2-6-0 CGR NG 0-4-0T CGR NG 0-6-0T CGR NG 4-6-2T CGR Type A CGR Type B CGR Type C
List of South African locomotive classes South African locomotive history

Locomotives of South Africa
Steam	7' ¼" gauge East London 0-4-0VB Table Bay 0-4-0ST Table Bay 0-4-0T Table Bay 0-4-0WT 4' 8½" gauge Cape 0-4-0T Blackie Cape 0-4-2 Cape 2-4-0T CGR 0-4-0ST Aid Natal 0-4-0ST Durban Natal 0-4-0WT Natal Natal 4-4-0T Perseverance 3' 6" gauge Tank engines CGR 0-4-0ST 1873 CGR 0-4-0ST 1874 CGR 0-4-0ST 1881 CGR 0-4-0ST 1881 Coffee Pot CGR 0-6-0ST CGR 0-6-0T CGR 2-6-0ST 1900 CGR 2-6-0ST 1902 CGR 1st Class 0-4-0ST 1875 CGR 1st Class 0-4-0ST 1876 CGR 1st Class 2-6-0ST CGR 1st Class 4-4-0T CGR 2nd Class 4-4-0T CGR 3rd Class 2-6-0T CGR Railmotor CSAR Class C CSAR Class E CSAR Rack 4-6-4RT CSAR Railmotor Durban's Congella Durban's Edward Innes Durban's John Milne Durban's Sir Albert Port Elizabeth 0-4-0ST Kowie Railway 0-6-0T Kowie Railway 4-4-0T Metropolitan & Suburban 4-6-2T NGR 2-6-0T Durban & Pietermaritzburg NGR Class I 2-6-2T NGR Class K 0-4-0ST NGR Class K 0-6-0ST NGR Class K 2-6-0T NZASM 10 Tonner NZASM 13 Tonner NZASM 14 Tonner NZASM 18 Tonner NZASM 19 Tonner NZASM 32 Tonner NZASM 40 Tonner PPR 26 Tonner PPR 35 Tonner Portuguese SAR Class A SAR Class B SAR Class C SAR Class C1 SAR Class C2 SAR Class D SAR Class E SAR Class F SAR Class G SAR Class H SAR Class H1 SAR Class H2 SAR Class J SAR Class K SAR Railmotor SAR Dock 0-4-0ST SAR Dock 0-4-0T SWA 2-8-0T 3' 6" gauge Tender engines CGR 1st Class 2-6-0 1876 BP CGR 1st Class 2-6-0 1876 Kitson CGR 1st Class 2-6-0 1879 CGR 1st Class 2-6-0 1891 CGR 1st Class 4-4-0 CGR 1st Class 4-4-0TT CGR 2nd Class 2-6-2TT CGR 3rd Class 4-4-0 1883 CGR 3rd Class 4-4-0 1884 CGR 3rd Class 4-4-0 1889 CGR 3rd Class 4-4-0 1898 CGR 3rd Class 4-4-0 1901 CGR 3rd Class 4-4-0 1903 CGR 4th Class 4-4-2 CGR 4th Class 4-6-0TT 1880 CGR 4th Class 4-6-0TT 1882 CGR 4th Class 4-6-0TT 1882 Joy CGR 4th Class 4-6-0TT 1884 CGR 5th Class 4-6-0 1890 CGR 5th Class 4-6-0 1891 NGR Havelock NGR Class I SAR Class Exp 1 SAR Class Exp 2 SAR Class Exp 3 SAR Class Exp 4 SAR Class Exp 5 SAR Class Exp 6 SAR Class S SAR Class S1 SAR Class S2 SAR Class 1 SAR Class 1A SAR Class 1B SAR Class 2 SAR Class 2C SAR Class 3 SAR Class 3A SAR Class 3B SAR Class 4 SAR Class 4A SAR Class 5 SAR Class 5A SAR Class 5B SAR Class 6 SAR Class 6A SAR Class 6B SAR Class 6C SAR Class 6D SAR Class 6E SAR Class 6F SAR Class 6G SAR Class 6H SAR Class 6J SAR Class 6K SAR Class 6L SAR Class 6Y SAR Class 6Z SAR Class 7 SAR Class 7A SAR Class 7B SAR Class 7C SAR Class 7D SAR Class 7E SAR Class 7F SAR Class 8 SAR Class 8A SAR Class 8B SAR Class 8C SAR Class 8D SAR Class 8E SAR Class 8F SAR Class 8R SAR Class 8X SAR Class 8Y SAR Class 8Z SAR Class 9 SAR Class 10 SAR Class 10A SAR Class 10B SAR Class 10C SAR Class 10D SAR Class 11 SAR Class 12 SAR Class 12A SAR Class 12B SAR Class 13 SAR Class 14 SAR Class 14A SAR Class 14B SAR Class 14C 1st SAR Class 14C 2nd SAR Class 14C 3rd SAR Class 14C 4th SAR Class 15 SAR Class 15A SAR Class 15B SAR Class 15C SAR Class 15CA SAR Class 15E SAR Class 15F SAR Class 16 SAR Class 16A SAR Class 16B SAR Class 16C SAR Class 16D SAR Class 16DA 1928 SAR Class 16DA 1930 SAR Class 16E SAR Class 17 SAR Class 18 SAR Class 19 SAR Class 19A SAR Class 19B SAR Class 19C SAR Class 19D SAR Class 20 SAR Class 21 SAR Class 23 SAR Class 24 SAR Class 25 SAR Class 25NC SAR Class 26 SAR Katanga SWA 2-8-0 3' 6" gauge Articulated engines CGR Fairlie CGR Kitson-Meyer SAR Class FC SAR Class FD SAR Class GA SAR Class GB SAR Class GC SAR Class GCA SAR Class GD SAR Class GDA SAR Class GE SAR Class GEA SAR Class GF SAR Class GG SAR Class GH SAR Class GK SAR Class GL SAR Class GM SAR Class GMA SAR Class GO SAR Class HF SAR Class KM SAR Class MA SAR Class MB SAR Class MC SAR Class MC1 SAR Class MD SAR Class ME SAR Class MF SAR Class MG SAR Class MH SAR Class MJ SAR Class MJ1 SAR Class U 2' 6" gauge Cape Copper John King & Miner Cape Copper Britannia Cape Copper Caledonia Cape Copper Clara Cape Copper Condenser Cape Copper Scotia Namaqua Copper Pioneer Walvis Bay 2-4-2T Hope 2' & 600mm gauges ACR Class NG-G16A CGR NG 0-4-0T CGR NG 0-6-0T CGR NG 4-6-2T CGR Type A 2-6-4T CGR Type C 0-4-0T NGR Class N 4-6-2T SAR Dutton SAR NG 0-4-0T SAR Class NG1 SAR Class NG2 SAR Class NG3 SAR Class NG4 SAR Class NG5 SAR Class NG6 SAR Class NG7 SAR Class NG8 SAR Class NG9 SAR Class NG10 SAR Class NG-G11 SAR Class NG-G12 SAR Class NG-G13 SAR Class NG-G14 SAR Class NG15 SAR Class NG-G16 SWA Class Ha SWA Class Hb SWA Class Hc SWA Class Hd SWA Jung SWA Zwillinge
Electric	Amcoal Class E38 SAR Class ES SAR Class ES1 SAR Class Exp-AC SAR Class 1E SAR Class 2E SAR Class 3E SAR Class 4E SAR Class 5E s1 SAR Class 5E s2 SAR Class 5E s3 SAR Class 5E1 s1 SAR Class 5E1 s2 SAR Class 5E1 s3 SAR Class 5E1 s4 SAR Class 5E1 s5 SAR Class 6E SAR Class 6E1 s1 SAR Class 6E1 s2 SAR Class 6E1 s3 SAR Class 6E1 s4 SAR Class 6E1 s5 SAR Class 6E1 s6 SAR Class 6E1 s7 SAR Class 6E1 s8 SAR Class 6E1 s9 SAR Class 6E1 s10 SAR Class 6E1 s11 SAR Class 7E SAR Class 7E1 SAR Class 7E2 s1 SAR Class 7E2 s2 SAR Class 7E3 s1 SAR Class 7E3 s2 Spoornet Class 7E4 SAR Class 8E SAR Class 9E s1 SAR Class 9E s2 SAR Class 10E SAR Class 10E1 s1 Spoornet Class 10E1 s2 SAR Class 10E2 SAR Class 11E SAR Class 12E Spoornet Class 14E Spoornet Class 14E1 TFR Class 15E Spoornet Class 16E Spoornet Class 17E Spoornet Class 18E s1 TFR Class 18E s2 TFR Class 19E TFR Class 20E TFR Class 21E TFR Class 22E
Gas-electric	SAR Gas-electric
Diesel	3' 6" gauge Diesel-electric PRASA Class Afro 4000 SAR Class DS SAR Class DS1 SAR Class 31-000 SAR Class 32-000 SAR Class 32-200 SAR Class 33-000 SAR Class 33-200 SAR Class 33-400 SAR Class 34-000 SAR Class 34-200 SAR Class 34-400 SAR Class 34-500 SAR Class 34-600 SAR Class 34-800 SAR Class 34-900 SAR Class 35-000 SAR Class 35-200 SAR Class 35-400 SAR Class 35-600 TFR Class 35-800 SAR Class 36-000 SAR Class 36-200 SAR Class 37-000 Spoornet Class 39-000 TFR Class 39-200 TFR Class 43-000 TFR Class 44-000 2' gauge Diesel-electric SAR Class 91-000 3' 6" gauge Diesel-hydraulic SAR Class 61-000 3' 6" gauge Electro-diesel Spoornet Class 38-000
List of South African locomotive classes South African locomotive numbering and classification