The O-Rings in a simple Ball Valve cannot be accessed so there is no way to replace them. When the valve starts to leak, the whole Valve has to be replaced. If you want to access the O-Rings, you must buy a Ball Valve that has one or two unions. The Ball Valve shown here has a single union that will allow you to pull out the Valve Stem and replace damaged O-Rings. You will still have to cut out the Valve on the side that has no union.
CUT OUT BALL VALVE - Since this Ball Valve only has one union, you will have to cut the non-union side out of the system piping. Use a sharp hacksaw and leave enough room in the piping to install the Ball Valve back with a coupling.
REATTACH PIPE END OF VALVE - Glue on the pipe end of the Ball Valve onto the system piping using a straight connector. Make sure the handle of the Valve is orientated up or in the position you want it.
CHECK FOR LEAKS - Look for leaks around the Union Collar and the Valve Stem Shaft. If the Valve is on the suction side of the pump, spray the top of the Valve with a soapy solution and look for soap bubbles being sucked into a suction leak. If the Valve is on the discharge side of the pump, look for water squirting out around the valve union or shaft.