318 CONTROLLING INSECTS AND DISEASES 



The Engine. Gasoline engines of the vertical type pro- 

 vide the power on most out- 

 fits. It is better to have an 

 over-size engine running well 

 within its resources than a 

 smaller one extended con- 

 stantly to its limit of per- 

 formance. Seldom, if ever, 

 should the engine be of less 

 than 2 horsepower; one of 3 

 horsepower is necessary for an 

 outfit of medium capacity. 

 For duplex and triplex pumps, 

 successively larger engines 

 will be required as the ca- 

 pacity increases. Larger ma- 

 chines, delivering 15 gallons 

 or upward per minute, require 

 engines capable of developing 

 6 to 10 horsepower, and the 

 largest machines develop up 

 to 35 horsepower. The num- 

 ber of cylinders varies from 

 one on the small outfits to 

 four on the giant machines. A 

 very good source of power and 

 one very commonly used to- 

 day is the power take-off from 

 the tractor. This can drive 

 pumps ranging in capacity 

 from 15 gallons per minute up 

 to the largest built (Fig. 113). 



The engine must be hauled 

 about the orchard. It should 

 therefore be as light as is compatible with durable and reliable 

 performance. Simplicity of operation, a minimum of parts, 



(John Bean Mfg. Go.) 



Fig. 111. A true pressure regulator 

 has two valves. When the pump is 

 running, but no spraying is being 

 done, the upper valve opens to 

 take the load off pump and engine. 

 A relief valve merely diverts ex- 

 cess material back to spray tank, 

 but does not relieve engine and 

 pump. 



