108 



Brake Horse Power Required to Operate Plunger Pnmpti. 



Type of Engine. 



The above table will give the size of the engine. The driving power 

 must be either a gasoline engine, steam engine, or electric motor. The 

 methods of connecting the engine with the pump have been already con- 

 sidered. Other factors being equal, direct connection is preferable when 

 possible. A few general considerations of the types of engine are given in 

 the following paragraphs. 



Steam Engine. 



For small plants irrigating a few acres, the steam engine, although very 

 reliable, is practically out of the question because it requires a licensed 

 engineer whose salary would be prohibitive. However, for larger areas 

 and where coal is cheap, it may be cheaper than either a gasoline engine or 

 electric motor. For large plants operated continuously it may be economy 

 to install an efficient boiler and a high grade compound condensing, triple 

 expansion, or quadruple expansion, steam engine, in order to decrease the 

 fuel cost. For small plants operated only for short periods during the 

 irrigation season it is much more important to decrease the cost of instal- 

 lation. The interest on the capital invested and the depreciation of the 

 plant are very important items of cost as compared to the fuel cost. For 

 these reasons unless the acreage is large and the lift very high, the steam 

 plant will consist of a semi-portable locomotive type boiler and an ordinary 

 slide valve steam engine. 



Gasoline Engines. 



A gasoline engine is fairly reliable if it is strongly built and operated 

 with care. Cleanliness and proper attention are necessary. All parts and 

 bearings should be kept in fine adjustment and properly oiled, by examin- 

 ing the engine at least every two or three hours. The circulating water 



