PUMPING WATERS. 85 



sesses the advantage of strength, and simplicity of 

 construction, low first cost, simple foundations, and 

 ease of erection and repair. A well-designed centri- 

 fugal pump will discharge more water for a given 

 power than any other kind. Centrifugal pumps can 

 be erected in very awkward places sometimes ; they 

 will work equally well with the shaft vertical or hori- 

 zontal, but the suction should not be greater than 

 7 ft., and when placed below the water level it is an 

 advantage. They are very useful for raising dirty 

 water, as they have no valves. The arrangement 

 essentially consists of a series of curved blades, 

 mounted on a spindle and made to revolve in a cast- 

 iron case. When so, a partial vacuum is created 

 which provides the suction at the same time. Cen- 

 trifugal force impels the water towards the outer 

 circumference of the blades, where it accumulates 

 pressure and is so raised to the desired height. All 

 centrifugal pumps run at a high rate of speed. When 

 two or more pumps are combined in one casting on 

 the same shaft and bed-plate, the water passing from 

 the first to the last, and finally to the delivery, the 

 combination is known as a multi-stage pump, and 

 such pumps deliver water to a greater height than 

 would be possible with a single stage pump. 



The subject of deep well pumps has already re- 

 ceived attention. In many cases pumps of this kind 

 are indispensable, although even the best are some- 

 times far from satisfactory, and many engineers 

 prefer- an entirely different system of raising water 

 from wells. It is hardly likely that circumstances 

 will be once for all in favour of such a device, because 

 the dominating question is a supply of compressed 



