A subterranean well valve assembly includes a valve mounted within an annular housing which is actuated by an annular plunger co-axially mounted within the housing. The plunger is longitudinally shiftable to open the valve, in response to a fluid pressure signal. Within the housing, releasable latches are provided for engaging an annular groove, thereby temporarily locking the plunger in its lower position. The valve assembly also includes a permanent lock open mechanism comprising an annular locking mandrel, including a latch element. Longitudinal movement of the mandrel locks the mandrel in place, thereby interfering with subsequent retraction of the plunger from locked position.