Garratt locomotive

A Garratt locomotive is a type of steam locomotive invented by British engineer Herbert William Garratt that is articulated into three parts. Its boiler, firebox, and cab are mounted on a centre frame or "bridge". The two other parts, one at each end, have a pivot to support the central frame; they consist of a steam engine unit – with driving wheels, trailing wheels, valve gear, and cylinders, and above it, fuel and/or water storage. Articulation permits locomotives to negotiate curves that might restrict large rigid-framed locomotives. The design also provides more driving wheels per unit of locomotive weight, permitting operation on lightly engineered track. Garratt locomotives produced as much as twice the power output of the largest conventional locomotives of railways that introduced them, reducing the need for multiple locomotives and crews. The principal benefit of the Garratt design is that the boiler and firebox unit are slung between the two engine units. As Oswald Nock wrote, the Garratt type holds several advantages over the Mallet type:This [the Mallet] was so designed to provide a very large engine unit, to be managed by a single crew, but to spread the dead weight over many axles and thus avoid excessive loads on the track and under-line bridges, and at the same time retain flexibility of wheelbase to facilitate operation on severely curved sections of line. The Mallet, having driving-wheel units beneath the boiler, retains the limitation in dimensions inherent in the orthodox type of steam locomotive, while the immense length of some of these machines is itself a handicap. Except with oil firing, ... one cannot put the cab in front. H.W. Garratt ... patented ... the idea of having a single large boiler slung on a cradle carried on two entirely separate engine units. ... The boiler could be developed to ideal proportions, unfettered by any wheels beneath it. It could be kept short, and of large diameter, which is the best possible form for securing a high rate of evaporation.

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Related publications (1)

This problem corresponds to refueling locomotives at different station yards during the course of its journey. Locomotive tanks have a fixed fuel capacity and prices of fuel vary across yards. In addition, there is a fixed cost for hiring a refueling truck ...

2010

Related concepts (2)

Track gauge conversion

Gauge conversion is the changing of one railway track gauge (the distance between the running rails) to another. If tracks are converted to a narrower gauge, the existing sleepers (ties) may be used. However, replacement is required if the conversion is to a wider gauge. Some sleepers may be long enough to accommodate the fittings of both existing and alternative gauges. Wooden sleepers are suitable for conversion because they can be drilled for the repositioned rail spikes.

Steam locomotive

A steam locomotive is a locomotive that provides the force to move itself and other vehicles by means of the expansion of steam. It is fuelled by burning combustible material (usually coal, oil or, rarely, wood) to heat water in the locomotive's boiler to the point where it becomes gaseous and its volume increases 1,700 times. Functionally, it is a steam engine on wheels. In most locomotives, the steam is admitted alternately to each end of its cylinders in which pistons are mechanically connected to the locomotive's main wheels.