The Victorian Railways S class was a class of 4-6-2 express passenger steam locomotive operated by the Victorian Railways (VR) in Australia between 1928 and 1954. Built when the VR was at its zenith and assigned to haul the broad gauge-leg of its Melbourne to Sydney interstate express passenger services, the S class remained the VR's most prestigious locomotive class until the advent of diesel electric locomotives in the early 1950s.
They were the first Pacific-type locomotives on the VR, as well as its first 3-cylinder locomotive type. Renowned for their power and speed, in the ten years that followed their introduction the running time of the premier Sydney express service they operated was progressively reduced by one and a half hours. These service improvements culminated in 1937 with the replacement of the Sydney Limited with the Art Deco streamliner Spirit of Progress, and the S class locomotives were fitted with streamlined casings to match the new train set. They were also equipped with long-range tenders to enable the entire journey to be run non-stop at a speed that remained for the next 20 years Australia's fastest train service.
Although only four S class locomotives were built, they were highly utilised. They ran up annual mileages double that of other classes of locomotives on the VR and by 1954 had run a combined total of approximately . However their size and heavy axle load made them unsuitable for regular service on any other lines than the North Eastern line, and so within six months of the introduction of the new B class diesel locomotives on the Spirit of Progress roster in April 1954 the S class had all been withdrawn and scrapped. Their scrapping was a catalyst for the rail preservation movement in Victoria to lobby for the preservation of remaining examples of other VR steam locomotives, resulting in the establishment in 1962 of the Australian Railway Historical Society Museum in Williamstown North.
History The S class locomotives were built to speed up principal express services, and to eliminate double-heading of services by their A2 class 4-6-0 predecessors. Although designed for normal operation at , they were credited as being capable of .
They were the final design of the Victorian Railways' Chief Mechanical Engineer Alfred E Smith, who had been responsible for the highly successful K class 2-8-0 and N class 2-8-2 designs, and was closely involved with the earlier A2 class 4-6-0, C class 2-8-0, and Dd class 4-6-0 designs.AHRS Railway Museum History 1900–1950
The S class was VR's first three-cylinder locomotive, and Smith's design was influenced by Nigel Gresley's Great Northern Railway A1 class 4-6-2 with its Gresley conjugated valve gear. The S class also displayed some American design influence in its use of bar frames rather than plate frames and the provision of a delta trailing truck.
Built at the VR's Newport Workshops, the S class locomotives were, at the time of construction of the first three, the largest locomotives to have been built in Australia, and had the largest boilers to have been constructed in the southern hemisphere.Dunn et al., Super Power on the VR – Part 1, p. 6 Another notable design innovation, the incorporation of all three cylinders and the smokebox saddle into a single casting, was the first of its type in the southern hemisphere and one of the largest single castings undertaken in Australia up to that time. That was only possible because a "set" was placed in the axle of the leading driving wheels, thus allowing all three cylinders to be in the same horizontal plane. That had the added advantage of avoiding many of the middle cylinder problems that beset Gresley's Pacifics.
The S class spent its entire revenue service life on the main North East line because its axle load was too high for regular service on any other Victorian Railways line. Although Annual Reports show the railways planned to upgrade the main Western line and build further S class locomotives to haul The Overland services between Ararat and Serviceton, exigencies imposed by the Great Depression and World War II meant the planned upgrade of that service never eventuated.
Although a numerically small class, limited to a single line, the S class was utilised extensively. By November 1929, the three locomotives then in service were reported to be doing work that would have taxed the capacity of five A2 class locomotives, yet their £53,000 ($106,000) capital cost was £2,000 ($4,000) cheaper than the five A2s, and they were further saving an estimated £3,000 ($6,000) per year in comparative operating costs. By 1936, they were averaging per year, with S303 having set a record annual mileage for Victorian Railways locomotives, travelling in one year. They were also noted for running between major overhauls, compared to an average for other locomotive classes in the VR fleet. By the time of their withdrawal from service, all had travelled well in excess of a million miles, with S302 the most travelled at over its 25-year, 2 month service life, averaging 4,773 miles (7,679 km) per month.Dunn et al., Super Power on the VR – Part 2, p. 9 S303 travelled in its service life of just 23 years, 6 months, averaging over per month.
Regular service: 1928–1937
On 19 March 1928, S300 hauled its first revenue passenger service between Seymour and Melbourne. After ten weeks of trials, it was regularly rostered on the key North East line Sydney Limited and Albury Express services unassisted, hauling trains comprising up to ten E type carriages plus luggage van over the 1 in 50 gradients that carried the line from above sea level in its first .
The new locomotive attracted considerable public interest, with details of its construction and trial running reported in the press. On 29 April 1928, S300 went on public display at Flinders Street station in conjunction with fund-raising efforts for the building of the Shrine of Remembrance. It was inspected by around 3,000 people.
With the delivery of a further two locomotives (S301 and S302) in February and April 1929,Dunn et al., Super Power on the VR – Part 1, p. 3 and the strengthening of the Murray River bridge at Albury to carry them, the S class displaced the older A2 class 4-6-0 locomotives from those services. The superior power of the S class had a profound impact on the timetable which, in July of that year, saw a cut of half an hour from the previous five-hour nineteen-minute northbound Sydney Limited schedule of A2-hauled trains.Dunn et al., Super Power on the VR – Part 1, pp. 3, 10 A fourth locomotive, S303, was delivered in November 1930. Its introduction enabled both ordinary and "limited" express services on the Albury line to be rostered for the S class, even if one of the class was in the workshops for repairs.
By 1931 however, a severe reduction in passenger traffic caused by the Great Depression saw the S class locomotives withdrawn from running the Sydney express services, and they were put to use on goods trains on the North Eastern line until passenger traffic picked up. As well as allowing the VR to deflect criticism of its investment in building the S class locomotives, the move also enabled the new X class goods locomotives to be reassigned from the Albury line to mainlines in other areas of the state, where they were reportedly used to considerable benefit.
By 1934, the S class locomotives were back in passenger service and, in an effort to improve their appearance, the VR broke with its policy of using an all-black locomotive livery and, between May and October, outshopped the class in a glossy, wagon red livery.Dunn et al., Super Power on the VR – Part 1, pp. 3, 16
By July 1935, the S class locomotives had accelerated services once again. With the line speed limit raised to , the S class-hauled Sydney Limited was reported as being the fastest train in the Southern Hemisphere, with the southbound service running at an average speed of , including the five-minute stop at Seymour to take on water. The non-stop run between Seymour and Albury was also Australia's longest.
Design improvements
Initial tests with the prototype S300 revealed only average performance for a locomotive of such size. Further detailed study revealed that insufficient valve travel and narrow port openings were impairing performance and, based on that study, improvements were made to the three S class locomotives that followed, including a reported change from the travel, lap valve gear, shared with the N and X class locomotives, to a travel, lap valve gear.
When first constructed, the trailing delta truck axle under S300 had insufficient lateral damping and, when running at high speed around curves, tended to knock the track out of the ideal transition spiral alignment.
In April 1935, S303 was equipped with the VR's Modified Front End, to improve drafting and reduce cylinder back pressure. Tests showed a resultant increase in indicated horsepower from 1,560 hp (1,160 kW) to 1,920 hp (1,430 kW) at 30 mph (48 km/h).Dunn et al., Super Power on the VR – Part 1, pp. 3, 13 Smoke deflectors were fitted the following month to compensate for the reduced uplift of smoke from the redesigned exhaust and, between July 1935 and July 1936, the remainder of the class was similarly upgraded.
The boilers were modified to a design that incorporated a combustion chamber, arch tubes and thermic siphons. However, unlike its close relative the X class Mikado, the S class was not modified with Belpaire fireboxes, and retained its round-top boiler shape.
During dynamometer car testing with S301 in 1937, a maximum output of 2,300 drawbar horsepower (1,720 kW) at 45 mph (72 km/h) was recorded.
In common with the LNER Gresley Pacifics from which the design of the S class valve gear was derived, the centre cylinder and the big end bearing of the centre connecting rod were located beneath the steam chest and boiler, where they were exposed to great heat. That caused a problem, which was exacerbated by the reduced ventilation following the fitting of the streamlining associated with the Spirit of Progress service from 1937 onwards, coupled with the faster running speeds involved. The grease-lubricated locomotive axles also suffered overheating problems from the sustained higher-speed running. The VR dealt with both problems by switching to a "red oil" lubricant with a higher resistance to heat.
A final modification, late in the life of the S class, was their conversion to oil firing from February 1951 onwards. The scarcity of Maitland coal, and the unsatisfactory performance of the locomotives when using coal from other fields, began to adversely affect their performance and running schedules.
Spirit of Progress: 1937–1954
From November 1937, the S class was assigned to haul the VR's luxurious, all-steel, fully air-conditioned streamliner, the Spirit of Progress. At the time, they were the only passenger locomotives on the VR with enough power to take the Spirit'''s eleven-car trailing load of unassisted over the 1 in 50 gradients between Melbourne and Albury.Dunn et al., Super Power on the VR – Part 1, p. 25
Preparations for the S class to haul the Spirit of Progress were made as early as February 1937, when S301 was fitted with streamlined cladding that dramatically altered its appearance, together with a long-range tender, with capacity for the of water and of coal which enabled the train to travel the entire journey non-stop, at an average speed of northbound and southbound.Dunn et al., Super Power on the VR – Part 1, p. 3 S302 was similarly modified during August 1937. While initially painted wagon red, by November both streamlined locomotives were repainted in the royal blue and gold livery, designed to match the new Spirit of Progress carriages.
Along with their streamlining for the Spirit of Progress, the locomotives were also named after prominent figures in early Victorian history: