Centrifugal governor

One of the advantages of working at a university: You always find people who enjoy playing :-)

Last summer, I visited the ThinkTank museum in Birmingham. I already posted about all their cool water features back then (the balancing ball or cool fountain, for example). But there is this one movie that I took that I have been wanting to post about but never got round to actually doing it.

MVI_9284
A centrifugal governor

What you see above is a part of a steam engine. As you will see in the movie below, it seems that all it does is spin around. But that is really not true. This little device is connected to the engine’s output shaft by a belt. So basically its speed is proportional to the engine’s speed. The faster the engine goes, the faster the little device rotates. The faster it rotates, the more the centrifugal force acts on the two massive metal balls, driving them away from the axis. As they move outwards, levers close the valve supplying steam to the engine, hence reducing the engine’s speed. As the engine slows down, so does the little device, and the two balls come back towards the axis, hence re-opening the valve. This negative feedback loop continues until a steady state is found. So this innocently-looking device really regulates the speed of the engine! Pretty cool, huh?

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