n o r e w o P Heritage
MARSHALL POWER UNITS
THE PULLEY Marshall single-cylinder tractors were a popular and successful source of stationary power on the farm and in forestry too. Peter Longfoot discusses their design and looks at some of their most common belt pulley applications
T
oday, when we have an almost reliable supply of electricity that can be counted on 24 hours a day, every day, and electric motors of all shapes and capacities to turn that power into useful work, it is easy to forget that this wasn’t always the case. The provision of electricity to farms and country businesses was a long time coming and some outlying farms remained unconnected to the mains until the early 1960s. Of course, such farms were not without electricity as practically all had provided themselves with a generating set for lighting. The earliest form of mechanical power to reach the farm was the portable steam engine, whose main application was for power to drive a threshing machine. Portable steam engines even supplied the power for the very earliest cable ploughing systems. It was not unusual to see a windmill with a pulley on a shaft on an outside wall, this arrangement enabling a portable steam engine to be used to provide power to the windmill when the conditions were very still. When the same conditions prevailed there were instances when a portable steam engine was belted to a drainage windmill in the Fens to drive the scope wheel to prevent local flooding. All this demonstrates the
ABOVE: The Marshall T20 stationary power unit was based on the engine used in the 15-30 and 18-30 tractors. Marshall had high hopes for its two-stroke full diesel engines, but the numbers sold could be counted on one hand. importance of portable stationary power before the general distribution of electricity. As steam power gave way to the tractor, this importance did not diminish to any great extent. The design of practically every early tractor incorporated the provision of a belt pulley, this attachment even being available as a standard item on most crawler tractors.
There are stories of Ransomes’ own Caterpillar Diesel 50 driving a dynamo by belt to supply power to crucial parts of the Ipswich factory during power shortages. International Harvester sales literature of the 1930s focused heavily on the ‘Triple Power’ features of its tractors, namely the drawbar, power take-off and belt pulley. Many manufacturers quoted belt horsepower as well as drawbar and brake horsepower in their literature. The Nebraska Tractor Tests included belt horsepower test figures from their instigation in 1920 until the late 1950s, when PTO horsepower began to replace the belt test.
A
lthough farms usually had a generating set for lighting, mainly for the house and also if there was a poultry enterprise, the available power was not sufficient to drive such barn machinery as grinding and rolling mills, chaff cutters, root slicers and occasionally a water pump. Although these tasks on many farms were carried out by small petrol stationary engines, it was here that the tractor with its belt pulley came into its own. The tractor could easily be moved around the farm to provide power for the barn machinery and the firewood saw bench. And of course the tractor wasn’t slow in replacing the traction engine to drive and move the threshing outfit,
“ When a Marshall traction engine was retired it was almost always replaced with a Marshall tractor”
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