A flow sub for use with a drill string, comprising: a tubular housing having a longitudinal bore therethrough and a flow port through a wall thereof; a ball disposed in the housing above the flow port, having a bore therethrough, and rotatable relative to the housing between an open position where the ball bore is aligned with the housing bore and a closed position where a wall of the ball blocks the housing bore; a seat disposed in the housing above the ball for sealing against the ball wall in the closed position; a sleeve disposed in the housing and movable between an open position where the flow port is exposed to the housing bore and a closed position where a wall of the sleeve is disposed between the flow port and the housing bore; and an actuator operably coupling the sleeve and the ball such that opening the sleeve closes the ball and closing the sleeve opens the ball; wherein the sleeve is longitudinally moveable relative to the housing and the actuator is operable to close the ball after the sleeve is at least partially open and open the ball before the sleeve is fully closed; characterised in that the actuator comprises: a cam longitudinally movable relative to the housing and operably connected to the ball; a body disposed adjacently below the ball, connected to the housing, and having a j-slot through a wall thereof; a j-slot formed through a wall of the sleeve; and a pin fastened to the cam and extending through the body j-slot and into the sleeve j-slot. a tubular housing having a longitudinal bore therethrough and a flow port through a wall thereof; a ball disposed in the housing above the flow port, having a bore therethrough, and rotatable relative to the housing between an open position where the ball bore is aligned with the housing bore and a closed position where a wall of the ball blocks the housing bore; a seat disposed in the housing above the ball for sealing against the ball wall in the closed position; a sleeve disposed in the housing and movable between an open position where the flow port is exposed to the housing bore and a closed position where a wall of the sleeve is disposed between the flow port and the housing bore; and an actuator operably coupling the sleeve and the ball such that opening the sleeve closes the ball and closing the sleeve opens the ball; wherein the sleeve is longitudinally moveable relative to the housing and the actuator is operable to close the ball after the sleeve is at least partially open and open the ball before the sleeve is fully closed; characterised in that the actuator comprises: a cam longitudinally movable relative to the housing and operably connected to the ball; a body disposed adjacently below the ball, connected to the housing, and having a j-slot through a wall thereof; a j-slot formed through a wall of the sleeve; and a pin fastened to the cam and extending through the body j-slot and into the sleeve j-slot. a cam longitudinally movable relative to the housing and operably connected to the ball; a body disposed adjacently below the ball, connected to the housing, and having a j-slot through a wall thereof; a j-slot formed through a wall of the sleeve; and a pin fastened to the cam and extending through the body j-slot and into the sleeve j-slot.