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 them from closing into the water stream. Hence they do not "impact" or "knock" as advertized. They do however "popup" [
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Also They have 2 inputs for water pressure. One of the side, and one on the bottom. I can see the screen on the bottom hole to filter debris, but i cant see a screen in the hole on the side "which i'm using."
Any tips to lubercate the plastic heads? or sand them? I cannot even find instructions on how to dississemble the damn things or a exploded view for that matter.
BEansly