A method and apparatus for controlling fluid flow with a quarter-turn ball valve with seats operated to lift off the sealing surface of the ball valve prior to ball rotation and to reseat upon completion of the ball rotation. One embodiment shown relates to a quarter-turn ball valve having a rotatable cam with an eccentric camming disk that engages a cam pocket in the ball seats to reciprocally lift off the sealing surface of the ball valve prior to ball rotation and to reseat upon completion of the ball rotation. An embodiment is also shown that provides filler pieces that restrict that flow around the ball valve whenever the ball seats are lifted off the surface of the ball valve.