Proper nozzle selection should take into consideration the type of application, your pressure setting, distance from the substrate, and the nozzle number size.Your pump must be capable of producing the proper amount of PSI needed for the total GPM flow rate of all the nozzles required for the application. For instance, a #4.0 nozzle will always do 2.0 GPM at 1000 PSI. See the flow rate chart to match your nozzle size to your pump.