page_title: South African Class 25 4-8-4
section_title: Characteristics
hierarchical_section_title: South African Class 25 4-8-4 / Characteristics
caption_attribution_description: English: SAR Class 25 3511 (4-8-4) banjo face Builder's Number: NBL 27371 Type: Condensing Location: Beaconsfield, Kimberley, Northern Cape
context_page_description: The South African Railways Class 25 4-8-4 of 1953 was a condensing steam locomotive.
  Between 1953 and 1955, the South African Railways placed ninety Class 25 condensing steam locomotives with a 4-8-4 Northern type wheel arrangement in service. The Class 25NC which was placed in service at the same time was a non-condensing version of the Class 25 condenser.
context_section_description: The boiler was similar to the Watson Standard no. 3B boiler of the Class 15F, but with the distance between tubeplates reduced from 22 feet 6 inches (6,858 millimetres) to 19 feet (5,791 millimetres) by the addition of a combustion chamber. While this resulted in a slight decrease in the total evaporative heating surface, there was a 40% increase in the firebox heating surface and a better ratio of firebox to grate area. The boiler was lagged with Cape Asbestos mattresses, manufactured and fitted in South Africa.
  On the condensing locomotive, spent steam was recycled and condensed back to water for repeated use. Since the steam wasn't expelled up the chimney, the Class 25's smokebox contained a steam turbine-driven fan beneath the chimney to keep the draught going, with deflector plates that were supposed to prevent char from causing excessive wear on the fan blades.
  The smokebox of the Class 25 was similar to that of the Class 25NC, but with the front extended to accommodate the centrifugal blower which was driven by an exhaust steam turbine mounted under the front of the smokebox. Apart from the usual round smokebox door in the centre of the smokebox front plate, the complete front smokebox plate on both classes was hinged to the wrapper plate on the right hand side of the smokebox in addition to being bolted to the angle ring at the smokebox front, to facilitate less cramped access to the blower equipment, superheater header and tubes.
  The draught turbine gave the locomotive its characteristic whining sound while running. As delivered, the Class 25 had the usual round smokebox front, but this was later modified by adding a banjo-shaped extension to also cover the exhaust steam turbine. Spent steam was fed through a thick pipe on the engine's left hand side back to the condensing tender.
  The banjo-shaped extension modification to the front of the smokebox was found necessary to cope with the copious amounts of char generated by brittle Witbank coal and mechanical stoking, since the original Henschel design proved to have too little capacity to keep accumulated char away from the exhaust turbine. Most of the char was collected in the trough of the banjo at the bottom of the smokebox front from where it was periodically ejected through a vertical steam ejector pipe inside the banjo door which exhausted immediately in front of the chimney.
  In service, the turbine-induced draught of the Class 25 actually performed better than the regular draught of the Class 25NC. One advantage of the condenser was that while getting up steam, the blower could be opened at a boiler pressure of about 15 to 20 pounds per square inch (103 to 138 kilopascals) to start the fan spinning, which drew the fire and accelerated getting up steam pressure. On a non-condensing locomotive the blower would be weak while steam pressure was still that low.
  Timken roller bearings were used throughout, including on the three-axle tender bogies, the coupling and connecting rods as well as the crosshead gudgeon pins, while the locomotive's leading bogies and coupled wheels had Cannon-type axle boxes. Compared to earlier SAR practice, a novelty was the adoption of mechanical lubrication. A sixteen-feed lubricator was driven off the reversing link trunnion. Since the Class 25 was entirely mounted on roller bearings, very little effort was required to move these huge locomotives.
  The cylinders and frames were cast in one piece while the steel cylinders and steam chests were fitted with cast iron liners. The tender frame was also a one-piece steel casting. The Alligator type crossheads were split on the vertical centre line and clamped on to the end of the piston rods, which had three coned rings engaging in grooves in the crossheads. The original coupling rods differed from the usual in the provision of three independent rods, thereby doing away with four knuckle joints and pins.
  The locomotive was able to negotiate curves with a radius of 275 feet (84 metres), with ¹⁄₄ inch (6 millimetres) gauge widening and 4 ¹⁄₂ inches (114 millimetres) superelevation. The whee
caption: Banjo-face smokebox front
exif: {"Image ImageDescription": "", "Image Make": "SONY", "Image Model": "DSC-H1", "Image Orientation": "Horizontal (normal)", "Image XResolution": "72", "Image YResolution": "72", "Image ResolutionUnit": "Pixels/Inch", "Image DateTime": "2009:09:18 15:32:56", "Image YCbCrPositioning": "Co-sited", "Image ExifOffset": "8", "Thumbnail ImageLength": "[]", "Thumbnail Tag 0x5920": "[]", "Thumbnail Tag 0x525C": "[]", "Thumbnail Tag 0x2C39": "[]", "Thumbnail Tag 0x8A3C": "[]", "Thumbnail Tag 0xC9CB": "[]", "EXIF ExposureTime": "1/10", "EXIF FNumber": "28/5", "EXIF ExposureProgram": "Aperture Priority", "EXIF ISOSpeedRatings": "64", "EXIF ExifVersion": "0220", "EXIF DateTimeOriginal": "2009:09:18 15:32:56", "EXIF DateTimeDigitized": "2009:09:18 15:32:56", "EXIF ComponentsConfiguration": "YCbCr", "EXIF CompressedBitsPerPixel": "8", "EXIF ExposureBiasValue": "0", "EXIF MaxApertureValue": "3", "EXIF MeteringMode": "CenterWeightedAverage", "EXIF LightSource": "Unknown", "EXIF Flash": "Flash did not fire, compulsory flash mode", "EXIF FocalLength": "6", "EXIF FlashPixVersion": "0100", "EXIF ColorSpace": "sRGB", "EXIF ExifImageWidth": "1280", "EXIF ExifImageLength": "960", "Interoperability Tag 0x829A": "1/10", "Interoperability Tag 0x829D": "28/5", "Interoperability Tag 0x8822": "3", "Interoperability Tag 0x8827": "64", "Interoperability Tag 0x9000": "[48, 50, 50, 48]", "Interoperability Tag 0x9003": "2009:09:18 15:32:56", "Interoperability Tag 0x9004": "2009:09:18 15:32:56", "Interoperability Tag 0x9101": "[1, 2, 3, 0]", "Interoperability Tag 0x9102": "8", "Interoperability Tag 0x9204": "0", "Interoperability Tag 0x9205": "3", "Interoperability Tag 0x9207": "2", "Interoperability Tag 0x9208": "0", "Interoperability Tag 0x9209": "16", "Interoperability Tag 0x920A": "6", "Interoperability Tag 0xA000": "[48, 49, 48, 48]", "Interoperability Tag 0xA001": "1", "Interoperability Tag 0xA002": "1280", "Interoperability Tag 0xA003": "960", "Interoperability Tag 0xA005": "8", "Interoperability Tag 0xA300": "3", "Interoperability Tag 0xA301": "1", "Interoperability Tag 0xA401": "0", "Interoperability Tag 0xA402": "0", "Interoperability Tag 0xA403": "0", "Interoperability Tag 0xA406": "0", "Interoperability Tag 0xA408": "0", "Interoperability Tag 0xA409": "0", "Interoperability Tag 0xA40A": "2", "EXIF InteroperabilityOffset": "8", "EXIF FileSource": "Digital Camera", "EXIF SceneType": "Directly Photographed", "EXIF CustomRendered": "Normal", "EXIF ExposureMode": "Auto Exposure", "EXIF WhiteBalance": "Auto", "EXIF SceneCaptureType": "Standard", "EXIF Contrast": "Normal", "EXIF Saturation": "Normal", "EXIF Sharpness": "Hard"}