I have to think the engineers who designed sprinkler heads have a purpose for all the parts. Does anyone know what the vane is for and what happens if it is left out? The Rainbird impacts (MiniPaws and MaxiPaws, to name two) have a vane in the water stream just behind the nozzle. I expect it has something to do with 'straightening' the flow (turbulent to laminar) prior to the water hitting the nozzle. Any ideas? If you leave it out, what is the harm?