If you unscrew that Allen head adjusting screw, count the number of turns you make to be sure to return to where it wasIf you release pressure on all cyls. Remove the relief and it easier to get that small plug out that's held in by inside snap ring. They will tend to hold moisture and rust. That valve is a sort of relief as it's a circuit relief. Protects cylinders from a manual overload. Its setting is like 500 psi over main relief. They are all the same except for the pressure setting. The relief for the boom down circuit is set way lower than Main relief to protect The boom cylinders .