Why Pressure Adjustments are Not the Best Way to Change Nozzle Flow Rate

Learn why pressure adjustments are not recommended for changing nozzle flow rate and how to adjust spray with a centrifugal pump.

Why Pressure Adjustments are Not the Best Way to Change Nozzle Flow Rate

When it comes to altering the flow rate of a nozzle, pressure adjustments are not the most efficient or effective solution. A 4-fold increase in pressure is required for a 2-fold change in flow rate, making it an inefficient process. Moreover, operating pressures at the upper or lower limit of a nozzle's range can have an undesired effect on nozzle wear, average droplet size, and stripe uniformity. The performance of the nozzle is dependent on several factors, with spray pressure being the most critical.

Pressure affects the nozzle flow, the spray pattern (fan angle) and the quality of the spray (droplet size range). These all have an impact on coverage, overlap and dispersion of the aerosol, so it is important to get specific information about the nozzles from the manufacturer. If a pressure gauge is not available or difficult to assemble, a small accessory called a constant flow valve (CF valve) can be mounted just in front of the spray nozzle. This valve detects changes in spray pressure and modulates the size of the valve inlet port to maintain a constant flow at the tip of the nozzle.

Jet agitators should not be installed on the pressure regulator branch pipe as low pressure and intermittent liquid flow often produce poor results. To adjust spray with a centrifugal pump, open the arm shutoff valve, turn on the sprayer and open the throttle control valve until pressure exceeds 10 PSI. Lower pressures generate larger droplets, reducing drift potential while higher pressures create small drops for maximum plant coverage. The pressure relief valve must be replaced by a relief valve when using pressures greater than 200 PSI.

If necessary, spray pressure adjustments can also be made but larger pressure changes may be needed to eliminate major application errors. Use a smaller agitation nozzle if agitation is insufficient when the spray pressure is correct and the pressure relief valve is closed. Low pressures of 15 to 40 PSI may be sufficient to spray most herbicides or fertilizers but high pressures of up to 400 PSI or more may be needed to spray insecticides or fungicides. In conclusion, it is not recommended to use pressure adjustments to change nozzle flow rate due to its inefficiency and potential unwanted impacts on nozzle wear, average droplet size, and stripe uniformity.

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