Return Valve is built out of brass with a viton seal and a 1/4" compression fitting. This check valve is designed to keep a positive pressure on the system for immediate starts and quick shut offs. This is factory pre-set and needs no adjustment.
I tried several things to get rid of the flies, but nothing worked. I installed my Shoo-Fly system last year and have had no more fly problems ! I was shocked at how fast it worked.
Caryn Henry Barrel Horses - Deleon Springs, Fl 32130