Ok, I figured it out. I had to get my needle nose pliers and stretch the spring further to power through any sand that gets in the joint of the head. I think I pet a little to much pressure but it will have to do. Now I get to wire up my rain bird indoor computer. THe JOY!
I just read all the posts to stay away from orbit alltogether. BUT I'm on a VERY tight budget and installed 3 of these 55100 popup knockers and hit trouble. The part of the head on the spring that impacts the water is getting stuck open. Mind you that I tested them all before installing them to make sure the "flapper" as i call it is operating smoothly. Everythinbg worked fine untill i installed them ,of course... So now the all plastic heads except the spring, feel like they have sand stopping ...
