98 SPRAY APPARATUS 
mounted on skids or on wheels. Such outfits range in capacity from 4 
to 12 gallons of spray material per minute, and are operated at a pressure 
of 200 pounds or more. The pumps used may be of the large, single 
cylinder, single-action type, or double action, or multiple cylinder. 
The engines in the smaller and medium size outfits are usually of 13 
to 3 horse power, single cylinder, and either air or hopper cooled. In 
the recently designed, extremely powerful outfits, used for spraying 
tall trees from the ground, the engine is of the automobile or marine 
type, with two, three, or four cylinders. The main advantages of 
power outfits include the rapidity with which the work can be accom- 
plished, the saving of hand labor at pumping, and the high pressure at 
which the spray is applied. Where many trees are to be sprayed, the 
power outfit will do the work at less cost per tree than the less ex- 
pensive, smaller outfit. 
Compressed Air Outfits 
Compressed air sprayers are in use in some orchards. In this type 
of apparatus the sprayer itself consists simply of two large steel tanks 
mounted on skids or wheels, and fitted with the necessary leads of 
hose. One of the tanks is filled with the spray material, while in the 
other air is stored under considerable pressure, usually 160 pounds. 
Pipes connect the air tank with the liquid tank, and the spray material 
is agitated by arranging the inlet of air in such fashion that it comes out 
of a number of jets at intervals along the bottom of the liquid tank. 
The air is compressed at a central station by means of an air com- 
pressor using gasoline or other power. It is customary to have two 
or more of the sprayers, so that one may be at the central station re- 
celving its spray material and its charge of compressed air, while the 
other is in the orchard. Usually the air pressure is reduced to about 
80 pounds by the time a sprayer has discharged its liquid and is ready 
to return to the central station. The system has the advantage of 
rather rapid work, and of comparative simplicity, so far as the sprayer 
itself is concerned. Its disadvantages are the fact that it operates 
necessarily at a constantly changing pressure, thus tending somewhat 
to uneven work, and the high cost of installing the plant. 
