Watt Governer

8/7/2019 Watt Governer

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The Watt type Governor

Probably the most widely used governor in the early days, it is named the Watt governor because James Watt applied it to his early beam engines. He did not however invent itas it had been in use on wind and water mills many years before this. A belt or gearing from the engine crankshaft drives the input shaft 'm' causing the bevelgears 'l' to revolve and in turn rotate the vertical shaft 'a'. The bracket 'b' at the top of 'a'supports two arms 'c' which are pivoted at the top, at the end of the arms are two veryheavy metal weights 'B' partway along the arms 'c' are fixed two pivoted link arms 'd'



which link to a collar 'c' which rotates with them but is able to slide up and down shaft 'a'. The up and down motion of this collar is followed by a pair of pins 'f' which move a bellcrank 'g' which is in turn linked to a throttle actuating rod 'i' linked to a throttle or butterfly

valve in the supply of steam to the engines cylinder which can allow more or less steamthrough. At rest the governor weights are held in the lowest position by gravity, the throttle will bein its most open position. As the engine speed increases these weights rotate faster until centrifugal force exceeds that of gravity and they fly further outwards and as aresult of the linkages, upwards, this movement is transmitted to the trottle valve whichbegins to close. The faster the governor is driven the further out the weights move andthe more the throttle is closed, until the amount of steam it lets through balances thedemand and the engine speed stabilises.

If the load the engine drives is reduced it will increase speed, the governor restrictssteam flow more until the speed stabilises, if load is added to the engine the speeddrops, the throttle is opened more and more steam allowed in to compensate for thedemand. The Watt governor is a simple governor but is not terribly accurate where very finecontrol of speeds in needed and so was superceeded in many applications by morespecialised and accurate governors, however for many agricultural end pumpingengines where absolute speed was not essential it survived and can still be seen onnumerous preserved engines.

Expansion Governors



A similar effect but with a much more rapid response (although lower levels of efficiency) resulted when the expansion slide valve was driven either from an eccentricwhere governor movement varied the throw of the eccentric (and thereby altered therange of movement on the expansion valve as above) see also the .



Or as with the Hartnell expansion governor above, from a fixed eccentric via anexpansion link (l) and die block (h), the position of which is governor controlled andeither increases or decreases the travel of the expansion valve rod (k), admitting steamearlier or cutting it off earlier depending on speed or load (see also the description of theexpansion governor)

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Watt Governer