When a solenoid valve (also called an electric valve or automatic sprinkler valve) fails to close it is almost always because something is stuck inside it. This might be a grain of sand, a small twig, a insect, or even a tiny snail. To fix the valve you need to disassemble and clean...
The two check valves (1st & 2nd Check) will have different spring loadings. The check valves in an RP will open when something downstream of the RP in the piping system opens a water-using fixture, and as the water begins to flow to that fixture, the pressure drops. The pressure ...