How does pressure affect spray?

This very short article is all about the info-graphic.

Pressure is integral to how nozzles perform: Lower pressures reduce nozzle rate, increase median droplet size, and typically increase spray fan angle. Higher pressures increase nozzle rate, reduce median droplet size and typically reduce spray fan angle. In extreme cases, too low a pressure can collase the fan angle enough to reduce overlap and compromise coverage (Watch this, and this and if you’re still interested, this).

Pressure affects all aspects of spray quality. Using a flat fan nozzle as an example, a lower pressure increases the median droplet diameter, reduces the droplet count, reduces the nozzle rate and typically reduces the spray angle. Alternately, a higher pressure decreases the median droplet diameter, increases the droplet count, increases the nozzle rate and typically increases the spray angle. Always plan to operate a nozzle in the middle of its recommended range so it can handle small changes in pressure during spraying (such as from a rate controller, or changing PTO speeds on hilly terrain).

Pressure affects all aspects of spray quality. Using a flat fan nozzle as an example, a lower pressure increases the median droplet diameter, reduces the droplet count, reduces the nozzle rate and typically reduces the spray angle. Alternately, a higher pressure decreases the median droplet diameter, increases the droplet count, increases the nozzle rate and typically increases the spray angle. Always plan to operate a nozzle in the middle of its recommended range so it can handle small changes in pressure during spraying (such as from a rate controller, or changing PTO speeds on hilly terrain). Don’t operate an air induction nozzle below 30 psi, even if it’s rated for lower in the manufacturer’s table.

 

Pressure can be used to make minor changes to rate while spraying. This is how rate-controllers work to compensate for changes in ground speed and maintain a constant overall rate per hectare or per acre. However, pressure should not be used to make significant changes to nozzle rates. It takes a 4x change in pressure for a 2x change in rate, so it’s inefficient. Increased pressure increases nozzle wear and pressure changes may negatively impact the spray quality if the nozzle is pushed outside its recommended range.

It is far better to simply switch nozzles when a significant change in rate is required.