94 SMALL WATER SUPPLIES. 



used for pumping water by means of electric motor. 

 This, however, is not generally a wise proceeding 

 where no accumulators exist ; it is generally prudent 

 to make the pumping plant a separate unit. It must 

 not be supposed from the foregoing remarks that the 

 gas or oil engine provides at once the best way of 

 raising water. These machines, however good, cost 

 money in fuel and repairs, and before deciding on 

 any form of motive power, the engineer should make 

 quite sure that all natural sources of power have 

 been investigated and found wanting. We have 

 already discussed the hydraulic ram, but a flowing 

 river provides another source of power in the shape 

 of a turbine (water-wheels will not be discussed, 

 they are heavy, cumbersome machines, of low ef- 

 ficiency and out of date). Say, however, a stream 

 is gauged and found to provide at least 1000 gallons 

 per minute and a fall of 10 feet can be obtained. 



A gallon of water weighs 10 Ib. .*. 10 x 1000 x 10 

 = 100,000 foot-pounds per minute, which is equal to 

 -Vij A o -, 3 horse-power, from which a good turbine 

 would easily develop 2\ horse-power. If the fall were 

 20 ft. this would be doubled, and so on. The matter 

 in all cases demands attention, far more in fact than 

 is usually given to it. 



There are three ways in which water-power may be 

 used. For falls up to 20 ft. with large quantities of 

 water, the Jonval type of turbine is used ; for falls from 

 20 to 1 50 ft. a Girard turbine is the best ; while if the 

 supply is small but the head is great, say 1 50 to 500 or 

 over, a pelton wheel is a very serviceable motor. In 

 Britain the most usually occurring instance is the 

 first, and as the use of water-power is a comprehen- 



