CENTEIFUGAL PUMPS 631 



of adapting it to the high speeds of rotation common in the case of the 

 electric motor or steam turbine, its even torque rendering it particularly 

 well fitted for such a purpose, and the general tendency towards the 

 extended use of such motors has of recent years given a great impetus to 

 the development of the pump. 



The extent of this adaptability may be realised from experiments by 

 M. Plateau, 1 who, using a pump having a single impeller of 3'15 inches 

 diameter, and rotating at 18,000 revolutions per minute, obtained an 

 efficiency of approximately 60 per cent, when pumping against 863 

 feet head. 



Indeed, to such an extent have the possibilities in design responded to 

 the demands made upon them in recent years, that the centrifugal pump 

 promises to replace the reciprocator to an ever-increasing extent in every 

 class of work, except where the volume of water to be handled is very 

 small in comparison with the working head. 



For mine drainage, the motor-driven centrifugal has the advantage of 

 requiring no expensive emplacements ; while for elevator work this motor- 

 driven pump, with an automatically controlled rheostat to regulate the 

 discharge, has an advantage in that since the delivery pressure cannot 

 increase to any large extent, no bye-pass is required. With a reciprocating 

 pump this bye-pass is essential and involves a loss of energy by leakage. 



Applied to dredging operations, the centrifugal pump is capable of 

 removing sand, gravel, or clay broken up by a water jet or mechanical 

 agitator, the amount of solid varying up to 40 per cent, of the volume 

 handled. With a mixture containing 15 per cent, of gravel or 35 per cent. 

 of fine sand, efficiencies of about 45 per cent, may be attained. 



In its essentials the pump may be looked upon as a reversed inward 

 radial or mixed flow turbine, having the wheel vanes driven in the opposite 

 direction to that of rotation in the case of the turbine, and discharging 

 outwards. 



If the pump be filled, the rotation of the wheel produces a forced vortex 

 in the contained water, with a consequent increase of pressure in an 

 outward radial direction and a tendency to outward flow. If the speed of 

 rotation is sufficiently high, this increase in pressure becomes more than 

 sufficient to balance the statical pressure of the delivery head and flow 

 takes place. A partial vacuum is thus produced at the centre of the 

 wheel and water is forced up through the supply pipe by atmospheric 

 pressure to take the place of that discharged outwards by centrifugal 

 action. 



i Engineer, March 7, 1902 (p. 23). 



