South African Railways 4-8-4 Locomotives in South_Africa

Class 25/Class 25NC (Locobase 2483)

Firebox heating surface included 37 sq ft of circulators.

Surprising locomotive in many respects, the least of which is the sheer size of the engine carried on a Cape gauge track. More significant was the use, in 90 of these engines, of a condensing tender, creating "puffers that never puff." Instead of letting the exhaust blast out of the stack it was conveyed back to a large tender with condensing coils arrayed along its sides. There the steam cooled and the tender collected the water for reuse. In the Karoo Desert this system was worth the extra expense. A characteristic feature of these engines was the "banjo" face; viewed head-on, the boiler was shaped like a teardrop with its pointed end down.

Hollingsworth (1982) notes that the smokebox blower, used to create a draft over the fire, suffered severe fan blade abrasion at first from the ash and grit in the exhaust stream. After the problem was solved by Henschel (the designer and supplier of the first engine), the engines operated successfully. He comments: "It is a strange sensation to watch a 25 starting a heavy train; there is complete silence apart from the whine of blower fan." In the 1970s, all of the condensers were converted to match their 50 non-condensing sisters. The 50 NCs were shared by NBLC (10) and Henschel (40).

See also locomotive diagrams published on []

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Class 26 (Locobase 3084)

Data from diagram presented on David Wardale's screen in the Ultimate Steam Page, [], last accessed 5 July 2009.

David Wardale is a disciple of LD Porta, a steam locomotive designer who, like Andre Chapelon, believed that this type of engine hadn't exhausted its potential. Wardale took the opportunity afforded by his access to South African steam to tinker first with a Class 19D locomotive and then, more ambitiously with a Class 25NC. The result was the L D Porta, also known as the "Red Devil" for its all-red paint job.

Although limited by money and the need to use existing parts when available, Wardale still was able to combine Porta's major improvements to conventional steam locomotive design. At one end was the Gas-Producer Combustion System (GPCS) and at the other was the double LemPor exhaust. The GPCS layout creates a more benign environment for complete combustion on the grate by reducing the amount of air coming up from below and admitting air through seven secondary air inlets in the sides of the firebox. This puts oxygen where it's needed most -- in the heated air over the coal fire where the unburned, but still volatile products of coal heating can be found. In addition, notes David Forsyth, the "ferroequinologist" whose explanation I rely on, exhaust steam led back to the ashpan helps reduce clinker buildup (which would encase coal in an hard coat) by cooling the grate.

Up ahead is the LemPor double-nozzle stack arrangement which smooths the draft over the fire. Other modifications to the Red Devil included a larger superheater (ten more elements than the 25NC) with an ingeniously simple baffle that acts to maintain a constant superheat temperature at all speeds. Improved piston valves, compressed air sanding, larger steam chests, and a feedwater heater were some other changes to the basic 25NC design.

The result was what one might expect from a well-thought-out manipulation of basic steam locomotive design principles. Coal consumption plummeted by more than a third (35%, says Forsyth, 38% says the Ultimate Steam Page). Forsyth also reports a 27% decrease in water consumption and a 50% increase in maximum drawbar horsepower. In fact, says the Ultimate Steam Page, sustained drawbar horsepower readings reached 4,000 hp.

Unfortunately for Wardale and the Red Devil, she was also unique and what's more a direct contradiction of the move toward diesel and electric locomotion. "The momentum of 35 years of stagnation in steam locomotive design," says the USP, " was too much for Wardale to overcome."