Greek - Roman Water Power #3

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Greek - Roman Water Power #3

Postby Marcus Minucius Audens » Tue Sep 27, 2016 5:43 pm

>>>> Greek - Roman Water Power #3 <<<<

>>> Undershot Water-wheel <<<

The next type of water-wheel is the undershot wheel, so called because the water pushes the paddles from the bottom of the wheel. This water-wheel is often also referred to as the “Vitruvian” which comes from the author’s description (Vitruvius, X. 5). In this respect, the undershot water-wheel can also be referred to as a horizontal shaft water-wheel because the drive shaft of the wheel is horizontal. This will require some sort of conversion device or devices to convert the horizontal drive to a vertical drive in order to power a gravity fed grain grinding machine. This requirement is in agreement with the author Lucretius when he said of the water-wheel, “It is also used for corn milling, the design being the same except there is a gear wheel on one end of the axle . . .” There is no mention of a vertical axle.

The structure that is described is quite simple to understand. It is constructed as follows; a spoked wheel with an unknown diameter, which has some paddles or vanes around the edge of said diameter. In his description Vitruvius calls them ‘pinnae’ (a word used elsewhere to mean the wing feathers of a bird). These paddles are then driven, by the water pressure of the stream, river, or whatever, and that turns the wheel.

The undershot wheel really only requires two things outside of the wheel; a vertical wall beside a river or stream. Now if you find that the water supply is limited for some reason then the channel to the wheel should be narrowed, in order to increase the speed of the water flow to have an impact directly on the wheel paddles. We know that to double the speed of the water is to increase power by eight times. The potential energy of a water-wheel can be easily worked out quite simply by the speed of the water and the depth of the water-fall. The undershot wheel has a great advantages for cost since no pit is required and any river or stream-side situation can be utilized (This can also result in a possible reduction of transport costs). In addition there will be no engineering costs or time involved in raising the water supply to a necessary height. The undershot wheel is known for it’s ability absorb kinetic energy from moving water. The generated torque is depending on the difference between the velocity of the water on arrival and the speed of the paddles as the wheel turns. To put it another way, the wheel generates power by slowing down the water. So, if you decide to load the wheel with more work (using bigger millstones or heavier buckets on a bucket chain), the wheel will rotate more slowly but will also develop more torque.


>> J. G. Landels, “Engineering In the Ancient World,” (Univ. of Calif. Press, Berkeley, 1981).

Respectfully Submitted;
Marcus Audens
Marcus Minucius Audens

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