The Hartnell Governor
Stationary steam engines, traction engines, portable and semi-portable engines all require some method of steam regulation to enable the operator to maintain adequate control over the machine. A device known as a governor is the piece of equipment used for this purpose. Numerous types of governors have been designed and put into use. It is widely accepted that the Watt governor may be one of the oldest, if not the oldest, design which can still be found in use on numerous applications around the world today. This article, although introducing the Hartnell Governor to the best of my ability, assumes the reader to have an understanding of the basic functions of governors in general. Mr. Hartnell* designed his governor circa 1875 and at the time it was considered to be of superior design to other governors of the day. It rotated between 500 and 600rpm and by utilising smaller fly balls and less parts, the internal friction was less than that of others. His original design consisted of the previously accepted method of a spring loaded rotating sleeve which altered the position of a bell crank and valve rod connected directly to a control valve fitted into the steam inlet pipe. The control valve either reduced or increased steam admission to the engine as required. When the steam engine increased in speed, possibly due to reduced loading of the engine, the fly balls would be forced out by centrifugal force thus moving the sleeve against, as in this case, spring tension. As the fly balls moved out, the central sleeve would be forced upwards which in turn moved the bell crank, valve rod and control valve in the correct direction to minimise steam flow and therefore decrease the speed, of the slightly over revving engine, back to its normal operating speed. Although the above description is reasonably typical for the majority of fly ball type governors, the Hartnell Governor had better stability against its strong spring, increased sensitivity due...
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