Abstract: A method and apparatus for operating a ball valve in a test tool string for a subterranean well, including a tubular actuator for the ball valve which is movable from a closing position of the ball valve to an opening position and beyond the opening position to a lock setting position, preventing the return of the tubular actuator to the ball valve closing position until the cycle of additional movements of the tubular actuator is accomplished. A metal-to-metal seal is provided for the ball valve and a larger than normal biasing force derived from a spring and a trapped pressurized gas is applied to the tubular actuator in its valve position to insure the integrity of the metal-to-metal seal.