IRRIGATION 231 



weight of a gallon of water). This will give 

 the weight pumped per minute. Multiply 

 this by the total lift in feet. This will give 

 the number of foot-pounds of energy required 

 per minute. Divide this by 33,000 (the num- 

 ber of foot-pounds in a horse-power) and the 

 result will be the number, of horse-power re- 

 quired. Pumping outfits are only about 50 

 per cent, efficient, so that the results ob- 

 tained by the above are doubled in actual 

 practice. On the average one horse-power 

 will pump 30 gallons per minute to the height 

 of loo feet. In pumping water against press- 

 ure in a pneumatic tank, extra power will 

 be required. Extra power will also be re- 

 quired when the water; is pumped for any 

 considerable distance, on account of the fric- 

 tion of the pipes. The frictional loss in feet 

 of lift for each 100 feet of pipe of various 

 sizes is shown in the following table. 



Gallons Size of Pipe 



permin. ^ in. 1 in. 1^ in. 1^ in. 2 in. 2- l / 2 in. 



Frictional Loss 

 10 29.9 7.3 1.4 1.0 0.28 0.09 



40 461.0 110.0 37.0 14.9 3.7 1.2 



