306 



AGRICULTURAL ENGINEERING 



is expensive, and it is well-nigh impossible to maintain suf- 

 ficient high pressure by hand to do the best kind of spraying. 

 Power. Steam engines have been used to some extent 

 as a source of power for spray pumps, or steam has been used 

 directly in direct-acting steam pumps. The great weight 

 of the steam boiler has caused its replacement by the gasoline 

 engine almost entirely. The gasoline engine is cheap in first 



Fig. 193. A power sprayer. 



cost, cheap in operation, and is light, which make it especi- 

 ally adapted to the purpose. 



The first requisite of a gasoline engine for a spraying out- 

 fit is reliability. It must operate under adverse conditions, 

 and there should be sufficient capacity to operate continu- 

 ously without overheating. 



Pumps. The plunger pump with outside packing of the 

 duplex or triplex type is now being generally used in the 



