portable steam engines :
A portable engine is a small steam engine, mounted on wheels or skids, which is used for driving machinery using a belt from its flywheel. It is not self-propelled and is towed to the work site by horses or bullocks, or even a traction engine. Portable engines were used mainly for driving agricultural machinery, such as threshing machines. In industrialised countries they are no longer used for commercial purposes, but preserved examples can often be seen at steam fairs driving circular saws or other equipment for demonstration purposes.
: traction engines
A traction engine is a wheeled steam engine used to move heavy loads, plough ground or to provide power at a chosen location. The name derives from the Latin tractus, meaning 'drawn', since the prime function of any traction engine is to draw a load behind it.
road locomotives :
Designed for haulage of heavy loads on public highways, it was not uncommon for two or even three to be coupled together to allow heavier loads to be handled.
The characteristic features of these engines are very large rear driving wheels fitted with solid rubber tyres; three-speed gearing (most traction engine types have only two gears); rear suspension; and belly tanks to provide a greater range between the stops needed to replenish water. All these features are to improve the ride and performance of the engine, which used to be used for journeys of hundreds of miles. Most road locomotives are fitted with a winch drum on the back axle. This can be used by removing the driving pins that secure the rear wheels, allowing the drive train to power the winch drum instead of the wheels.
: crane engines
A number of road locomotives are fitted with a crane boom on the front. The boom pivot is mounted on the front axle assembly, and a small steam engine is mounted on an extension to the smokebox in front of the chimney. The small steam engine is used to power a cable winch for raising and lowering a hook. These road locomotives can be used to load a trailer as well as haul it to a new location. They are often referred to as 'crane engines'.
steam rollers :
A steamroller (or steam roller) is a form of road roller - a type of heavy construction machinery used for levelling surfaces, such as roads or airfields - that is powered by a steam engine. The levelling/flattening action is achieved through a combination of the size and weight of the vehicle and the rolls: the smooth wheels and the large cylinder or drum fitted in place of treaded road wheels.
: steam wagons
These were the earliest steam lorries and came in two basic forms. The earlier over-type designs resembled traction engines by having a cab built around a horizontal boiler with a round smokebox and chimney (eg Foden). And they resembled lorries in having a load-carrying body and being built around a chassis (so they cannot really be called traction engines).
The more modern under-type designs have the engine under the chassis (although the boiler remains in the cab), and generally resemble lorries rather than traction engines.
Early examples of either type had solid tyres, but various developments, including vertical boilers, enclosed cabs and pneumatic tyres were tried by companies such as the Sentinel Waggon Works in a bid to compete with internal combustion engine -powered lorries.
steam tractors :
In Great Britain, the term steam tractor is more usually applied to the smallest models of traction engine - typically those weighing seven tons or less - used for hauling small loads on public roads. Although known as light steam tractors, these engines are generally just smaller versions of the road locomotive.
They were popular in the timber trade in the UK, although variations were also designed for general light road haulage and showman's use.
: ploughing engines
A distinct form of traction engine, characterised by the provision of a large diameter winding drum driven by separate gearing from the steam engine. Onto the drum a long length of wire rope was wound, which was used to haul an implement, such as a plough, across a field.
The winding drum was either mounted horizontally (below the boiler), vertically (to one side), or even concentrically, so that it encircled the boiler. The majority were under-slung (horizontal), however, and necessitated the use of an extra-long boiler to allow enough space for the drum to fit between the front and back wheels. These designs were the largest and longest traction engines to be built.
Mostly the ploughing engines worked in pairs, one on each side of the field, with the rope from each machine fastened to the implement to be hauled. The two drivers communicated by signals using the engine whistles.
A Showman's Road Locomotive or Showman's Engine is a steam-powered road going locomotive designed to provide power and transport for a travelling fair. Similar to other road-going traction engines. Showman's engines were normally distinguished by the addition of a full length canopy, a dynamo mounted in front of the chimney, and brightly coloured paintwork. This was used to generate electricity to illuminate various fairground rides. Motion of the rides was normally provided by belt drive from the locomotive's flywheel.
Above descriptions have been taken from Wikipedia