FARM IMPLEMENTS Ol IRRIGATION. 183 



Centrifugal pumps are measured by the diameter of the 

 suction pipe. The discharge in cubic metres per minute 

 on lifts of about 3 metres is found approximately by the 

 following rule : - 



(Diameter in feet 2 ) x 10 = cubic metres per minute. 

 Thus a 12-inch 1 x 1 x 10 = 10 cubic metres per minute. 

 18 IT) x 1-5 x 10 = 22'5 

 36 3 x 3 x 10 = 90 

 48 4 x 4 x 10 = 160 



For easy calculation this rule gives fairly accurate 

 results. 



The speed of water in the suction pipe of a pump is 

 usually 2 \ metres per second although higher speed is 

 now often used. To attain this speed on a high lift the 

 engine runs correspondingly fast, and it is found that if 

 a large pump on a lift of 2\5 metres runs 70 revolutions 

 per minute it increases to 90 revolutions when the lift 

 is 3*50. Small pumps run faster than large ones as 

 regards revolutions per minute but the speed of the 

 tip of the fan is the same. 



The commonest sizes of pump in Egypt are of 8 and 10 

 inches and often these are run by engines of 8 and 10 H.P. 

 The engines are nearly always portable engines driving 

 the pump by a belt. Engines are rarely ever moved, and 

 so the expensive road wheels are only of service once in 

 getting the engine to its destination. Small fixed engines, 

 steadier in working and with parts more accessible, would 

 suit better. 



