Wellington & Manawatu 2-8-0 Locomotives in New_Zealand

Class Oa (Locobase 2710)

Data from [] accessed in January 2002 and from Baldwin Locomotive Works Specification for Engines as digitized by the DeGolyer Library of Southern Methodist University Volume 19, p, 77. See also "Serve Tubes in New Zealand Locomotives", The Model Engineer and Electrician, Volume 8 (29 January 1903), p. 98. Works number was 13908, 13913 in January 1894..

OS Nock (RWC III, pl 94) observes that building a Vauclain compound on a sub-standard gauge and putting all of the motion inside must have put the valve gear in a "very inaccessible position." Like all Vauclain compounds, single piston valves served each cast set of an HP and an LP cylinder; for this engine, the valve diameter measured 9" (229 mm).

Locobase found a report on the use of Serve tubes that most likely involved one of these locomotives. The trial "proved a total failure," claimed the account reproduced in the Model Engineer and Electrician. The 70-mm diameter tubes "required cleaning out twice as often as plain tubes, and gave great trouble from leakage, doubtless owing to the greater expansion and contraction of the interior ribs under variations in temperature." Six inches of plain tubes (i.e., without ribs) suffered "serious grooving."

"After a year's service, it was found necessary to replace all the Serve tubes with plain tubes."

Nevertheless, these engines carried on for years, eventually being taken into the New Zealand Government Railways when the W&M was absorbed in 1908. As engine #457, the locomotive continued in service until December 1929.

Class Ob (Locobase 4963)

Data from [] accessed in January 2002 and from Baldwin Locomotive Works Specification for Engines as digitized by the DeGolyer Library of Southern Methodist University Volume 14, p. 91. Works numbers were 9018 and 9021 in January 1888.

These were the first Consolidations for this little railroad and set the pattern for New Zealand 2-8-0s.

When the WMR was taken into the New Zealand Government Railways in 1908, they were renumbered 455-456 in the Ob class. They continued to operate until September 1929 (456) and March 1931 (455).

NB: The direct heating surface (including the firebox heating surface) is an estimate calculated by subtracting the calculated tube heating surface from the reported total evaporative heating surface from the baldwin_steam site.

Class Oc (Locobase 4964)

Data from [] accessed in January 2002 and from Baldwin Locomotive Works Specification for Engines as digitized by the DeGolyer Library of Southern Methodist University Volume 20 p. 199. See also James Marchbanks, "On the Use of 'Serve' Steel Tubes in a High-Pressure Boiler, and their Efficiency as Compared to Iron Tubes", Proceedings of the Institution of Civil Engineers, Volume CXLIX, 1902), presented in International Railway Bulletin, Volume 17 (Brussels: Weissenbruch, 1903), [621.133.3], pp. . Works numbers were 15054-15055.

The other Vauclain compound Consolidation batch delivered to the WMR, this was one of mixed batch produced in 1896). Compared to #13 (Locobase 2710) , this later engine was noticeably heavy with more closely spaced drivers. It hauled 250-ton trains over 27 miles (43.5 km) "over a rough, undulating section of line". The maximum grade northbound consisted of 5 miles of 1 in 40 (2.5%), using a helper engine, and 3 more of 1 in 56 (1.8%); southbound's maximum grade was 1 in 56 over 3 mile and 5 mile sections. Marchbanks describes what Locobase thinks is a curious operating practice, "the boiler pressure being alternately raised to its maximum then allowed to die down, as the various gradients were surmounted." Moreover, "conditions of service demanded that the engine should stand for about two hours at the end of each 27 miles run.

The biggest difference from the 13 was the use of Serve internally finned tubes. Marchbanks illustrated the difference between measuring heating surface area for these novel tubes when he rported that the heat-absorbing surface area ("i.e., the internal surface of the tubes with the hot gases") was 1,235 square feet (114.74 sq m), 490 sq ft more than the "heat-distributing surface of the tubes".

From the time the engine entered service, Marchbanks said, the Serve flues leaked from the at the firebox end. Although the W&M adjusted practice to emphasize a clean fire and even steam pressure while running downhill, they continued to leak. Further adjustments using rocking grates and preventing cold air from entering the firebox improved matters. But after six months of service, "odd tubes" began to leak and leaks at the smoke box end led to the discovery that the flues showed grooving. The boiler steamed well in both locomotives, but after 500 miles, the 16 was "noticeably duller".

At that point, the experiment ended with the W&M removing the Serve tubes and substituting plain charcoal-iron tubes. Marchbanks concluded that the innovation's problems stemmed from "the ribbed portion being so rigid that all vibrations were concentrated at the front end, which is the thinnest and weakest part of the tubes."

It was taken into the New Zealand Government Railways when the W&M was absorbed in 1908. Retirement came more than two decades later in July 1930.