Just my personal experience with the Maxi Paws...they are a HEADACHE. I have a system that had 23 of these impact heads, i ended up replacing them with Rainbirds 5000 plus rotors. Too much maintenance (cleaning) with the Maxi paws...kept getting stuck, they would not trip the return mechanism. I blamed it on low pressure, so i reconfigured my system (less heads per zone) this increased my pressure to about 45psi, i still had the same problem, not as often, though. I ended up pulling all of these heads off and replacing them with RB's 5000 plus rotors, this ended my dilema. I use to have to babysit the watering process, make sure i was there so if a Maxi paw got stuck, step on it. There is plenty of people on this site with knowledge way beyond mine in this matter...this is purely personal experience's with these Maxi Paw impact sprinklers. I DONT recommend them.