ANNUAL REPORT. 197 



over those of the regular single-acting type is that they main- 

 tain a continuous and uniform discharge. 



The douhlc-acting pump, on the other hand, is provided 

 with at least two sets of ports or valves. In this case the 

 cylinder is filled from one end by one stroke and emptied hv 

 the return stroke of the plunger, filling at the same time from 

 the other end. Pumps of this kind are usually horizontal and 

 operated with an upright handle by either one or two men. 

 They are of large capacity and seldom used on barrel outfits. 



The tzvo-cylindcr type consists, as its name implies, of 

 two independent cylinders, operated with a single lever or 

 handle. The cylinders may be either vertical, like Gould's 

 Monarch or horizontal like the Friend. 



Hydraulic pumps, of which Myers Hydraulic Pump is 

 an example, are those with which a large air chamber is used. 

 The liquid is forced into the air chamber under pressure by 

 means of check valves. It is discharged through the nozzles 

 by the force produced by the cushion of compressed air, 

 which may be maintained for several minutes after the pump 

 stops. Such pumps are frequently used with horse-power out- 

 fits for spraying field crops. 



The rotary or "clock" pumps, while easier of operation 

 than most other forms, are short lived and, for this reason, 

 have not given satisfaction. 



Agitators. Spraying outfits are generally equipped with 

 an agitator to insure the discharge of the spray liquid at uni- 

 form strength. The most common type of agitator is the 

 dasher, which works with either an up and down or a side 

 motion. With barrel outfits they are usually attached to, and 

 operated with, the handle of the pump, while with tank out- 

 fits they are operated either with a belt from the engine or by 

 means of a chain and sprocket on the wheel of the cart. Bet- 

 ter agitation may be obtained if the dasher has both side, and 

 up and down motions. Probably the best type of agitator is 

 that constructed in the form of a screw-propeller. In large 

 horizontal tanks, the use of a shaft bearing several "propel- 

 lers" and extending the full length of the tank, is recom- 

 mended. 



