CSAR Rack 4-6-4RT

The Central South African Railways Rack 4-6-4RT of 1905 was a South African steam locomotive from the pre-Union era in Transvaal.

In 1905, the Central South African Railways placed two four-cylinder rack tank locomotives with a 4-6-4 Baltic type wheel arrangement in service on the section between Waterval Onder and Waterval Boven. The locomotives were underpowered and proved to be failures in rack service, with the result that their rack mechanisms were removed in 1906 to convert them to ordinary two-cylinder tank locomotives.^[1][2]

Manufacturer

In 1905, the Central South African Railways (CSAR) placed orders with Vulcan Foundry for the construction of two 4-6-4 Baltic type rack tank locomotives for use on the rack section between Waterval Onder and Waterval Boven. According to the designs and specifications of CSAR Chief Locomotive Superintendent P.A. Hyde, the CSAR Rack locomotive was to have a bar frame, two cylinders with 18 inches (457 millimetres) bore and 30 inches (762 millimetres) stroke, and was to use the same drive system as the Nederlandsche-Zuid-Afrikaansche Spoorweg-Maatschappij 32 Tonner, CSAR Class G, which had proven satisfactory in rack service. The two locomotives were delivered in 1905, numbered 995 and 996, following on from the number range of the Class G rack locomotives.^[1]

The builders chose not to adhere to the original designs and specifications. The cylinder stroke was reduced to 20 inches (508 millimetres) and two inner cylinders of the same dimensions were added to drive the rack mechanism independently. A plate frame was used instead of the specified bar frame. The main plate frames were 1 ¹⁄₄ inches (32 millimetres) thick and were arranged outside the coupled wheels. The balanced flat slide valves were actuated by Joy valve gear.^[1][2]

The boiler capacity was not increased to compensate for the additional cylinders and, in service, trouble was experienced under working conditions. Tests showed that the locomotives could not maintain steam and had insufficient adhesive weight to prevent slipping on the steep gradient. The boiler had to generate the supply of steam while the engine passed through the tunnel at the head of the incline with the blast pipe not functioning, since the exhaust steam was diverted to the side tanks while the counter-pressure air brake system was in operation.^[1][2]

Characteristics

Even though it turned out to be a failure in service, the locomotive design had several novel features at the time.^[1]

Rack mechanism

The outside cylinders drove the coupled wheels and the inside cylinders drove a coupled pair of rack wheels. The rack wheels were carried on a frame, suspended from the widely separated leading and driving coupled wheel axles, which had an 8 feet 3 inches (2,515 millimetres) wheelbase.^[1][2]

Rather than the bar frame as specified, an outside plate frame was used to accommodate the inside cylinders. The connecting rods of the inside engine were not connected directly to the crank pins, but to projections on the coupling rods which actuated the rack gear. This method of coupling was unavoidable due to the restricted width of only 3 feet 3 inches (991 millimetres) between tyres.^[1][2]

To compensate for tyre wear on the coupled driving wheels, the rack axle bearings could be adjusted vertically, while the rack wheel teeth were of involute form to ensure correct action between adjustments. The inner cranks were of the disk type, with triangular circumferential grooves to take the cast-iron brake blocks of the rack engine hand brake.^[1][2]

Brake systems

The valve gear of the outside and inside sets of motion could each be separately reversed by its own screw gear, while each set also had its own independent regulators, injectors and feed pumps. The locomotive had steam brakes on all coupled wheels as well as both bogies, the first and last South African steam locomotive to be equipped with braked bogies. The coupled wheels and the rack engine's crank disks had separate hand brakes and the inside and outside piston pairs had separate counter-pressure air brakes. In addition, the locomotive had a combination ejector to work the train's vacuum brakes.^[1][2]

The Le Chatelier counter-pressure air brake system made use of the following:

• A valve in the base of the blastpipe isolated the cylinders from the smokebox, to prevent the ingress of hot gases and cinders when the motion was reversed.
• Air was drawn from outside the smokebox through a pair of non-return valves into the exhaust ports, from where it was compressed into the steam chests.
• The compressed air was allowed to escape into the atmosphere through a graduating discharge valve and a silencer, mounted behind the chimney.
• To take up the heat of compression and prevent overheating of the cylinders, a small water jet delivered a cold spray into the exhaust passages.^[1][2]

Cab

To protect the crew from the smoke and gases in the tunnel, the large cab was totally enclosed and had side doors and windows.^[1][2]

Service

Central South African Railways

Converted rack no. 0995, circa 1912

In spite of its advanced features, the CSAR Rack locomotive was a failure and was outperformed by the older and much smaller predecessor Class G rack locomotive. As a result, the rack mechanisms of both locomotives were removed within a year of their entering service, converting them to ordinary two-cylinder tank locomotives. Owing to their failure, the old 32 Tonners remained in service until 1908, when a new alignment with easier gradients, including a new tunnel, was constructed and the rack section could be abandoned.^[1][2][3]

Their failure can be attributed directly to the fact that two additional cylinders were introduced by the builders while the boiler capacity remained the same, which resulted in a locomotive with an inadequate steaming ability. In addition, the complicated rack mechanism led to perpetual maintenance problems.^[1][2]

South African Railways

When the Union of South Africa was established on 31 May 1910, the three Colonial government railways (Cape Government Railways, Natal Government Railways and CSAR) 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 was only implemented with effect from 1 January 1912.^[4][5]

In 1912, the locomotives were considered obsolete and were not classified or renumbered, but instead only had the numeral "0" prefixed to their existing numbers. Both locomotives were withdrawn from service by 1915, a mere ten years after being built.^[5][6]

References

Wikimedia Commons has media related to CSAR Rack (4-6-4T).

Locomotives of the Central South African Railways
3' 6" gauge	CSAR 0-6-0ST 1896 CSAR 4-6-0T 1887 CSAR Class 6-L1 CSAR Class 6-L2 CSAR Class 6-L3 CSAR Class 7 CSAR Class 8-L1 CSAR Class 8-L2 CSAR Class 8-L3 CSAR Class 9 CSAR Class 10 1904 CSAR Class 10 1910 CSAR Class 10-2 Saturated CSAR Class 10-2 Superheated CSAR Class 10-C CSAR Class 11 CSAR Class B 0-6-4T CSAR Class C 2-8-4T CSAR Class D CSAR Class E 4-8-0TT CSAR Class E 4-8-2T CSAR Class E 4-10-2T CSAR Class F CSAR Class M CSAR Mallet Saturated CSAR Mallet Stoker CSAR Mallet Superheated CSAR Rack 4-6-4RT CSAR Railmotor IMR 0-6-0ST 1896 IMR 4-6-0T 1887 IMR 46 Tonner 0-6-4T IMR 55 Tonner 2-6-4T IMR 7th Class 4-8-0 IMR 8th Class 4-8-0 IMR Reid Tenwheeler 4-10-2T IMR Western Australian 2-8-4T NZASM 10 Tonner NZASM 13 Tonner NZASM 14 Tonner NZASM 18 Tonner NZASM 19 Tonner NZASM 32 Tonner NZASM 40 Tonner NZASM 46 Tonner OVGS 1st Class 4-4-0TT OVGS 2nd Class 2-6-0 OVGS 2nd Class 2-6-0ST OVGS 3rd Class 4-4-0 OVGS 4th Class G 4-6-0 OVGS 5th Class K 4-6-0 1890 OVGS 5th Class K 4-6-0 1891 OVGS 6th Class L 4-6-0 OVGS 6th Class L2 4-6-0 OVGS 6th Class L3 4-6-0 PPR 0-4-0ST Natal PPR 26 Tonner PPR 35 Tonner Portuguese PPR 55 Tonner
2' gauge	CSAR Pankop
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