File:Chemical weed-control equipment (1948) (20416542430).jpg

Title: Chemical weed-control equipment
Identifier: chemicalweed389akes (find matches)
Year: 1948 (1940s)
Authors: Akesson, Norman B. (Norman Berndt), 1914-; Harvey, W. A. (William Alfred), 1914-1989
Subjects: Weeds; Spraying; Spraying equipment
Publisher: Berkeley, Calif. : University of California, College of Agriculture, Agricultural Experiment Station
Contributing Library: University of California, Davis Libraries
Digitizing Sponsor: University of California, Davis Libraries

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Nozzles for airplane spraying are tapped from the top or side of the boom and are generally controlled by quick shut-olf valves for each nozzle or group of noz- zles. The valves may be spring-loaded or positive-action, of either gas cook or pop- pet style. Some operators use automatic, spring-loaded ball valves similar to those on ground rigs. Quick shut-off valves are essential to stop the liquid flow at field boundaries. These valves are controlled (by the pilot) with a small cable running the length of the boom and back to the cockpit. Nozzles may discharge either a cone or fan type spray. The method described on page 19 for ground-rig booms, using suction on the boom while boom pressure is off, has been adapted to use by planes. The width or coverage of the spray is not so greatly affected by the length of the spray booms as it is by the wing span, the height the plane flys, the design and power of the plane, and arrangement of the boom and nozzles with relation to airstream. Drop- let size is greatly affected by the angle at which the nozzles discharge into the air- stream. Smaller droplets occur when the nozzles are directed against or across the airstream than when they are directed with it. Droplet size is mainly influenced by pump pressure, but the very small nozzle orifices will also decrease the aver- age droplet size, depending upon the type of nozzle. A compromise must be made between the small droplets which give more thorough coverage but have a tend- ency to drift, and the large droplets which settle fast but are not so efficient with respect to coverage. (The number of droplets per square inch varies in- versely with droplet size.) The average size deposited by correctly operating air- plane equipment is between 50 and 300 microns, at which size most weed spray materials react satisfactorily. Strainers are not generally used be- cause nozzle orifices are large. However, spray material must be carefully strained before it is placed in the plane tank. Some operators believe that a boom strainer reduces valve and nozzle plugging. A nurse and mixing tank is used to mix the diluent and chemicals and to trans- port them to the field from which the plane is operating. Because the time for discharging the spray load is very short, the other time consuming operations- flying to the landing field for refilling, and the refilling operation itself—should 39

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