The recommended normal operating pressure for normal flat fan nozzles is 20 to 30 psi. At these pressures, this type of nozzle will produce medium to thick droplets that are not as susceptible to drift as finer droplets that occur at pressures of 40 psi or more. You must operate the sprayer at a pressure that is in the middle of the operating pressure range of the spray nozzles you are using. For most flat fan nozzles, this will be approximately 40 PSI, but may vary depending on the specific nozzle.
Maintaining operating pressure in this range provides flexibility during operation to accelerate or decrease speed and maintain a constant speed as pressure increases or decreases accordingly. Applying more insecticide will not improve effectiveness, it will only waste time and increase costs. The application rate of modern insecticides is determined through careful laboratory and field evaluations, and taking into account all aspects of the pest and the conditions to which they are directed. Overapplication cannot provide more than 100 percent control and, when it exceeds label instructions, violates state and federal regulations on the proper use of insecticides.
Operational spray pressure is critical to maintaining proper spray droplet size, spray coverage, and application speed. The ideal spray pressure is sufficient to maintain a good spray pattern and distribution. Most hand pressurized sprayers are capable of maintaining a pressure of up to 40 psi. Most spray nozzles work effectively in the pressure range of 30 at 40 psi.
As the operating pressure changes, so does the flow rate of the spray nozzle. For example, a spray nozzle may have a flow rate. It's important to keep the application equipment operating at the right pressures. When spray pressures change, so does the spray angle of the nozzle. Allowing the spray pressure to decrease to a low level will negatively affect the spray angle and coverage area.
Pesticide labels provide the spray coverage required to maintain the optimal efficacy of the chemical being applied. Usually, a small change in nozzle flow can be achieved by increasing or decreasing pressure within the nozzle pressure limits. In most commercially available portable aerosol systems, air pressure is fixed (not adjustable) and liquid pressure is adjustable. If the operating pressure is too low, the spray nozzle will not produce a uniform spray pattern, and if the pressure is too high, it may cause droplets that are too fine or fog. If you maintain a constant speed and don't change the size of the nozzle, the speed will increase when you increase the pressure and will decrease when you decrease it.
