The A2 class is an express passenger locomotive that ran on Victorian Railways from 1907 to 1963. A highly successful design entirely the work of Victorian Railways' own design office, its long service life was repeatedly extended as the Great Depression and later World War II delayed the introduction of more modern and powerful replacement locomotives.
History The introduction of the A2 class marked a turning point in Victorian Railways locomotive design, as it was entirely designed by VR engineers of the newly established Locomotive Design Section and the entire class built in-house at Victorian Railways workshops.Pearce et al., p. 12
The design, which started as a stretched evolution of the 1903 AA class 4-4-0 with bogie tender, has been credited to Chief Draughtsman Ernest Victor Siepen, with overall supervision of Chief Mechanical Engineer T. H. Woodroffe. Previously this had been attributed to Alfred Ernest Smith, a later Chief Mechanical Engineer.
Production At this time, the Sydney Express was regularly double-headed in both directions between Melbourne and Seymour, due primarily to the gradients either side of the Great Dividing Range. A2 572 was trialled on this run and others for about a year, with minor improvements undertaken as they were found to be necessary. These included an altered design of forward frame stiffener (between the smokebox and leading bogie), additional bolts to hold the cylinders in place against the thrust of the pistons, and an additional cradle under the firebox backplate end of the boiler. However, the engine retained its distinctive flat-topped dome. Five more of the class, 574, 576, 578, 580 and 722, were ordered in 190, and production continued from them on.
Based on the success of the prototype A2572, a total of 125 Stephenson valve gear A2 locomotives were built between 1907 and 1915. The design was then altered to incorporate larger diameter cylinders, a higher pressure boiler and Walschaerts valve gear, and a further 60 locomotives of that design were produced between 1915 and 1922.
Regular service For over forty years, the A2was the main express passenger locomotive on the VR, hauling intrastate and interstate services. With a maximum permitted speed of ,Pearce et al., p. 21 the A2was instrumental in the acceleration of timetables on many lines in the years following its introduction. A2 locomotives famously hauled the Geelong Flier, the first named train in Victoria, which ran express once a day in each direction between Melbourne and Geelong in 63 minutes, running from Flinders Street station, later cut to 55 minutes, running from Spencer Street station. However, other Geelong trains, stopping at wayside stations, still took about 90 minutes or more to make the journey.
Due to their comparatively heavy axle load, A2 locomotives were initially limited to the principal mainlines, but gradual upgrades to secondary lines saw the route-availability of the class expand, together with the range of services they hauled. Their size also meant that the outside cylinders of the new locomotives did not quite clear the stone or timber coping of some existing station platforms, requiring those platform edges to be cut back slightly to allow the locomotives to pass safely.
With their comparatively high tractive effort (the Walschaerts A2 had a higher nominal tractive effort than any other VR locomotive, regardless of type, until the introduction of the C class 2-8-0 of 1918), they also saw widespread use as a fast goods locomotive, particularly later in their life. As early as the 1920s, it was reported as normal practice that A2 class locomotives requiring adjustment to axle boxes and other moving parts be swapped from passenger to lower-speed freight service to extract more work from them between overhauls. Reportedly, engine crews preferred the Stephenson engines for fast running, but Walschearts locomotives for heavy haulage, based on the ride quality.
A2s were also used to haul a number of special services, such as the Royal Trains for Australian tours of Prince of Wales and the Duke of York, in 1920Public Record Office Victoria Series VPRS 12800/P1 Item H 1027 retrieved 2 October 2006 and 1927 respectively. Towards the end of their lives, A2995 and 996 also had the distinction of hauling the last broad gauge Spirit of Progress service into Melbourne on 16 April 1962.
In 1928, the A2 was replaced on the principal North East line Sydney Limited and Albury Express services by the considerably more powerful three-cylinder S class Pacifics. However, new locomotive development ground to a halt during the 1930s, with the Great Depression severely affecting both VR traffic volumes and operating revenues, so the A2 continued to be the main express passenger power on all other VR mainlines.
In 1933, two A2 class locomotives set a haulage record for Victorian Railways when they headed a 75-truck wheat train from Benalla to Seymour.
Pairs of A2 class engines were regularly worked on the Melbourne-Ararat and Ararat-Serviceton portions of The Overland; common candidates included A2940, A2942, A2947, A2955, A2966, A2973, A2976, A2993 and A2994.
Design improvements Changes to the locomotive and tender designs slightly increased the roadworthy weight of engine and tender combined from to , and the maximum axle load increased by about a quarter-ton. The Walschearts design was heavier again, with a roadworthy weight of , and maximum axle load of .
Superheaters The majority of A2 locomotives were originally built with saturated steam boilers. The class were gradually fitted with superheaters (starting from A2842, built 1913, fitted 1915), and to differentiate between the two variants the saturated steam locomotives were renumbered as A1 class, each being reclassified as A2 class again when fitted with a superheater. The order to reclassify saturated engines to A1 was issued on 16 March 1929 and applied to 70 engines, but some of these were still carrying A2 plates in 1932.
All Walschaerts locomotives were intended to enter service with superheated boilers, but wartime shortages meant that of the first fifteen (983 to 997), only 991 and 992 were issued to service with superheated boilers., the others running with saturated boilers for a few years. As these engines were refitted, the cylinders were replaced to achieve a diameter, though thestroke length of was retained. Other changes included reducing the boiler pressure from to at 80% of maximum safe rated pressure, offset by the fitting of superheaters. The first engine upgraded was A2 820, and the work involved provision of new cylinder castings rather than reboring the prior set. Notably, around 1930, an Interstate Commissioners Conference agreed that superheated engines' tractive effort was to be calculated at 85% of maximum safe boiler pressure, against 80% for saturated engines.
The superheating equipment was of either the Robinson () or Schmitt () designs, either applied to the new-build Walschaerts locomotives. Engines upgraded were fitted with Robinson superheaters until 1929. From then, a new all-steel boiler and firebox was designed (in lieu of the prior copper inner firebox lining), and this style used ML5 equipment in lieu (); the steel boiler was interchangeable between the Stephenson and Walschaert locomotives, contingent on the safety valves being correctly set. Superheated engines were also fitted with mechanical lubricators.
Many engines were renumbered two or three times as the railways' management attempted to keep the two subclasses in different number blocks, and as the boundaries between the blocks shifted through the superheating program. The last of the A1 class, No. 808, was converted in October 1949.
Modified front end In 1933, C class heavy goods locomotive C 5 was equipped with a new front end, based on the Association of American Railroads (AAR) design of self-cleaning smokebox, to improve steaming qualities. This was an evolution of design updates provided to the S and X class engines from 1928, including requiring only one spark-arresting grate through the year, rather than needing a second grate in summer. These changes netted a 23% increase in power output at . Victorian Railways' Rolling Stock branch engineer Edgar Brownbill continued this work from May 1933, conducting tests with A2 974 between Melbourne, Bendigo and Seymour with diameter superheater tubes, for a net improvement of 40% increased drawbar horsepower at . These results were very promising, and in April 1934 A2998 was selected for a series of additional tests aimed at further front end improvement. These tests involved various chimney-choke-point and blastpipe nozzle diameters, ranging from to and to respectively. In September 1934, A2989 was the first to be fitted with the standard form of Modified Front End, and it completed a run from Bendigo to Spencer Street in 2 hours 10 minutes; A2 993 was the next converted, and the first with smoke deflectors fitted in November 1934.
Experiments were conducted, based on the work of Dr Wagner of the Deutsche Reichsbahn and E. C. Young of the University of Illinois, with final modifications to the A2 locomotive including: Revision of exhaust nozzle and chimney position and diameter, using Wagner's recommended ratios, with a larger diameter funnel, and a diameter low exhaust nozzle replacing the original diameter narrow-flanged chimney and diameter high exhaust nozzle Revision to the firebox grate, using a "rosebud" type grate with reduced air openings to improve fire stability under heavy load and give better firing qualities Replacement of full-length return bend superheater elements with -long elements
The sum result of the changes was a significant improvement in power and available tractive effort. Maximum drawbar horsepower increased about 40%, from at to at . The improvement was such that the VR was able to further accelerate services hauled by the A2, with the running time of the Melbourne to Bendigo express on the steeply graded line being cut from 162 to 145 minutes, and literally hours being cut from the schedule of the Melbourne to Adelaide Overland express.
However, a more recent review indicates that more appropriate exhaust values may have been to for the chimney choke point and to for the blastpipe nozzle diameter; and that suitable designs could have been adapted to the pre-existing chimney of the A2 class locomotive, without the later need to provide smoke deflectors.
The Modified Front End, which cost just £140 ($280) per locomotive at that time, was an extremely cost-effective improvement, and allowed the VR to defer new locomotive construction. The modification was so successful that not only was the entire A2 fleet converted during 1936–39, but also the C, K, N, S and X class locomotive fleets, and its principles were also incorporated into the design of all subsequent steam locomotives built or modified for the Victorian Railways.
Tenders