Regulated flow of insecticides

The spray programmes of malaria eradication projects are plagued with many uncontrolled variables in the amount of insecticide deposited on the sprayed surface. Speed of coverage, pressure, and nozzle delivery rate all vary from day to day, hour to hour, and minute to minute. All the variables have received attention, particularly nozzle erosion, which increases the delivery and results in the overtreatment of the surface by as much as 50%. For this reason, it is considered good economy in many programmes to throw away and replace all the used nozzle tips each month. Recent developments described in this paper, however, indicate that it may be possible to use nozzle tips for several months, in some cases for an entire season, and at the same time to obtain regulated discharge from the nozzle despite changes of pressure in the tank.