The adjustable stator is preset at the factory to match the nozzle installed in the rotor. The purpose of the stator is to maintain a consistent and desirable speed of rotation. Rotors that turn too fast cannot reach their published radius distance. Rotors that turn too slow will irrigate with a higher precipitation rate per revolution causing wet spots and run-off.
If nozzles are changed to a flow greater than the original factory nozzle, the speed of rotation will become faster unless the appropriate stator adjustments are made. This is because there is a greater amount of water passing the turbine that drives the gearbox. The opposite is true if a smaller flow nozzle is installed without adjusting the stator - the rotor will slow down. In extreme situations, the rotor may not rotate at all if the stator is not adjusted. Again, stator adjustments are not required unless the nozzle flow is being changed or, the stator was set incorrectly at some point in time.
Setting the stator is as simple as matching the stator setting number to the nozzle number being used in the rotor. For example, if the nozzle in use is #20, then the stator setting will be #20. To access the stator adjustment, first remove the riser’s filter screen.