Water Power: Building an Overshot Water Wheel

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Gravity turns the overshot water wheel. Water-carrying buckets on one side overbalance the empty ones opposite.
Gravity turns the overshot water wheel. Water-carrying buckets on one side overbalance the empty ones opposite.
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Diagram shows standard positing of the wheel, flue, and foundation. As the headwater rises or falls, the sluice gate may be adjusted to meter the correct flow to the wheel.
Diagram shows standard positing of the wheel, flue, and foundation. As the headwater rises or falls, the sluice gate may be adjusted to meter the correct flow to the wheel.
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For highest efficiency, the buckets must carry their load almost to tail water before beginning to spill.
For highest efficiency, the buckets must carry their load almost to tail water before beginning to spill.

Often seen beside a picturesque rural mill, an overshot water wheel possesses two excellent characteristics: considerable mechanical efficiency and easy maintenance. Many have remained in service for decades, and now lend a nostalgic charm to their surroundings.

Operated by gravity, the overshot wheel derives its name from the manner in which water enters the buckets set around its periphery. Pouring from a flume above the wheel, the water shoots into buckets on the down-moving side, overbalancing the empty ones opposite and keeping the wheel in slow rotation.

Since such a wheel may be located near but not actually in the stream, it offers endless landscaping possibilities for a country home where a stream with sufficient flow is available. If a site on dry ground is chosen, the foundation may be constructed dry and the water led to the wheel and a tailrace excavated. With very little effort, the scene may be turned into an attractive garden spot, the wheel becoming both a landscaping feature and a source of power.

It should be noted, however, that an overshot wheel is practical only for a small-capacity output. How much power it will produce depends upon the weight of water the buckets hold and its radius, or lever arm. Expressed in another way, the output depends upon the weight of water transported and the height, or head, through which it falls while in the buckets. For maximum efficiency, the wheel must use the weight of the water through as much of the head as possible. Therefore, the buckets should not spill or sling water until very near tail water.

Power Increases with Width

  • Published on Mar 1, 1972
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