Garratt

A Garratt (often referred to as a Beyer Garratt) is a type of steam locomotive that is articulated into three parts. Its boiler is mounted on the centre frame, and two steam engines are mounted on separate frames, one on each end of the boiler. Articulation permits larger locomotives to negotiate curves and lighter rails that might restrict large rigid-framed locomotives. Many Garratt designs aimed to double the power of the largest conventional locomotives operating on their railways, thus reducing the need for multiple locomotives and crews. The Garratt articulated locomotive was developed by Herbert William Garratt, a British locomotive engineer who, after a career with British colonial railways, was the New South Wales Railways' Inspecting Engineer in London. Garratt first approached Kitson & Co, but his idea was rejected, perhaps because that company were already committed to the Kitson-Meyer. He then approached Beyer, Peacock and Company, who were only marginally more interested. In 1907 Beyer, Peacock & Co. submitted a proposal for a 2 ft (610 mm) gauge 0-4-0+0-4-0 Garratt to the New South Wales Government Railways, which was not proceeded with. The following year a design for a 2 ft gauge Mallet locomotive was submitted in reply to an enquiry from the Government of Tasmania. This was followed with a submission for a Garratt based on, but a little heavier than, the New South Wales proposal. This proposal was accepted, and two locomotives were built in 1909, which became the K class. The K class had to cope with 99' radius curves and 1 in 25 gradients. Unlike in Garratt's patent, Tasmanian Railways insisted on a compound arrangement with cylinders facing inwards, in order to reduce the distances between both the main steam pipe and the high-pressure cylinders, and between the high-pressure and low-pressure cylinders. This made the locomotive unnecessarily complicated and placed the high-pressure cylinders directly underneath the cab, making it uncomfortably hot, especially in summer. The pattern was not repeated on later Garratt designs. Only one more Garratt locomotive, again built by Beyer, Peacock & Co. in 1927, was produced with compound propulsion for the Burma Railways. Early design and construction difficulties involved the steam-tight flexible connections between the boiler unit and the power units. These were solved by Beyer, Peacock's designers after studying a description of the spherical steam joints used on a Fairlie locomotive built for the Ffestiniog Railway followed by a visit to the FR to observe these locomotives at work. The third Garratt (another 0-4-0+0-4-0, like the first two) was built in 1910 for the Darjeeling Himalayan Railway, and given the class letter 'D'. As with many early Garratt classes, this engine's dimensions and power were designed to be roughly equivalent to those of two of the line's existing 0-4-0T engines, although in practice it achieved only a 65% increase in loading. In 1911 Beyer, Peacock and Company built six 2-6-0+0-6-2 Garratts for the Western Australian Government Railways. The M class were followed by the Ms and the Msa class. They also formed the pattern for locos for the Victorian Railways narrow gauge G class, and for Australian Portland Cement. Beyer-Peacock built over a thousand Garratts, or Beyer-Garratts. The final Garratts to a Beyer-Peacock design were eight 2 ft (610 mm) gauge South African Railways Class NG G16 locomotives, built in 1967–1968. The order was placed with Beyer, Peacock and Co., but since the firm was in the process of closing down, it subcontracted the order to the Hunslet Engine Company. Hunslet's South African subsidiary, Hunslet-Taylor, in Germiston, built these locomotives using boilers manufactured by their mother company.