THE AIR LIFT PUMP 



703 



be determined in terms of h f and 7^. Writing h v = ^~ 



, and 



putting h f = J ** ' - (where v 2 is the mean square of the velocity 

 in the tube) this latter term may be taken as approximately equal to 



~~^^ 1 a o A ~ I i m which case the ratio V a -=- V w may be directly 

 A (f in * Z ^4. ' 



obtained in terms of h d , h s , A and/. 



The author has determined the values of /for a mixture of air and water 

 (the friction head being expressed in feet of a column of the mixture in the 

 tube) from the published data of a large number of trials on such pumps. 



Making the above assumption as to the value of v, the value of / varies 

 from *033 in the case of a 3-inch pipe with v = 12*16 f.s. to *023 in a 

 12-inch pipe with v = 6*5 f.s. In every case / has a value very 

 approximately six times that obtaining for the flow of water alone at the 

 same velocity. 



In practice the following approximate values of V a -f- V w are found to 

 give the best results : 



Efficiency of the Air Lift Pump. Assuming isothermal compres- 

 sion, the work done on the air during compression from p a to pi 



= p a V a log, P foot Ibs. 



Pa 



The useful work done by the air in raising V w cubic feet of water 

 through a height h d feet =.62'4 V w h d foot Ibs. 

 .*. Efficiency 



62-4 V m h* X 3 



r; = 



62-4 F, 



Pa V a log e ^ Pa log, f X V w (h d + h, + /*, 

 Pa Pa 



(2) 



On the assumption of adiabatic compression from p a to pi, the work done 

 on the air = 3'463 p a V a j ( pl } - i[ foot Ibs., so that the efficiency 



( \PaJ > 



