CURRENT WHEELS FOR POWER AND RAISING WATER.
The natural flow of water in a current is probably one of the oldest and cheapest of the methods for obtaining power, or the lifting of water within moderate elevations, for a supply for irrigation and domestic purposes; and we propose, apart from the current wheel, to treat only of self-water-raising devices in this chapter.
Water wheels of various forms for this purpose have been used from time immemorial in Europe, Asia and Egypt, where the record gives examples of wheels of the noria class from 30 to 90 feet in diameter; the term noria having been applied to water wheels carrying buckets for raising water; the Spanish noria having buckets on an endless chain.
Records of a Chinese noria, of 30 feet diameter, made of bamboo, show a lifting capacity of 300 tons of water per day to a height of ¾ of the diameter of the wheel—velocity of current not stated.
For less quantity and greater elevation, these forms of wheel may have pumps attached to the shaft, by crank, that will give a fair duty for a high water supply.
For power purposes, as in the plain current wheel, Fig. 23, there are two principal factors in the problem of power—the velocity of the current and the area of the buckets or blades.
Fig. 23
Their efficiency is very low, from 25 to 36 per cent., according to their lightness of make and form of buckets. A slightly curved plate iron bucket gives the highest efficiency, thus ( to the current, and an additional value may also be given by slightly shrouding the ends of the buckets.
The relative velocity of the periphery of the wheel to the velocity of the current should be 50 per cent. with curved blades for best effect.