Conventional vs. Low Volume Sprayers 



Orchard airblast sprayers available today may for convenience 

 sake be placed in one of three major categories, i.e., conventional, 

 low volume and ultra low volume. 



The conventional type airblast sprayer commonly used today and 

 during the past decade was designed to apply both dilute and semi- 

 concentrate rates which ranged from 500 gpa to as little as 50 gpa. 

 These sprayers operate at a pump pressure from 30 to 400 psi that 

 force the spray mixture through a manifold on which several nozzles 

 (6 to 15 per side) are located. Variable nozzle sizes may be sel- 

 ected which regulate the sprayer delivery rate as well as the range 

 of droplet size produced. The droplets are discharged into the 

 airstream which range in velocity from 80 to 120 mph and in volume 

 from 25,000 to 90,000 cubic feet of air per minute (cfm) . Air volume 

 specifications for orchard airblast sprayers in the past have been 

 highly controversial and their accuracy questionable to the point 

 where they are not often used today. The droplet size produced by 

 these machines has a wide range from 10 to 600 mu depending on pump 

 pressure and nozzle orifice size. The conventional sprayers are 

 effective in the application of 50 gpa or higher but are limited in 

 the application of smaller amounts. 



In recent years sprayers designed to apply 5 to 20 gpa have 

 been introduced and widely used in many apple growing areas of 

 eastern United States. Similar type concentrate or low volume 

 sprayers have been used for the past 20-25 years in Europe, Africa, 

 Australia, Middle-East, Canada, and in several apple growing areas 

 of western United States. 



The low volume airblast sprayer differs from the conventional 

 type mainly in pump pressure, air velocity and air volume. Pump 

 pressure ranges from 25 to 100 psi. Nozzles used on these machines 

 vary from 3 to 12 per side and are either a hollow-cone swirl nozzle, 

 a spinning nozzle, or an air jet which does not use swirl plates or 

 discs. The spray droplets are formed when the spray mixture is 

 injected into the airstream which may vary in velocity from 130 to 

 200 mph and in volume from 15,000 to 25,000 cfm. The high velocity 

 airstream performs two major functions: 1) that of a shearing or 

 impact action in the formation of droplets which range in size from 

 10 to 110 mu; and 2) as carrier of the droplets to all parts of the 

 target areas at high enough velocity for impingement. 



Sprayers which may effectively dispense 1.0 to 3.0 gpa of spray 

 mixture are available and have been proven to be equal to other 

 sprayers in pest control. Uniform droplets are formed by a revolv- 

 ing porous sleeve powered by an electric 12 to 24 v DC motor. Sleeves 

 of porous metal or plastic are available which produce precisely con- 

 trolled droplets from 5 to 100 microns. The liquid pesticide formu- 

 lation or suspension in water are forced through the uniform pores 

 by centrifugal force generated by the spinning nozzle. The nozzles 

 are mounted in the airstream which may vary in volume and velocity 

 and the droplets are sheared off and carried to all parts of the tree. 



