To remove the valve assembly from the hydrant, shut off the water supply to the hydrant and remove the packing nut. Turn the stem clockwise until it is seated, but not overly tight. Loosen and turn the head nut assembly counterclockwise while turning the operating stem clockwise until the threads disengage from the head casting. The valve assembly will pull out with head nut.
To reinstall the valve assembly, unthread the valve assembly from the head nut assembly and push the valve assembly into the hydrant. The wing on the yoke nut goes in the groove inside the head. Start the stem screw thread into the yoke nut and turn the stem counterclockwise until it the head nut threads can be engaged in the head. Thread the head nut assembly into the head clockwise while turning the operating stem counterclockwise. Reinstall the packing nut.