A wellbore ball valve includes a ball-type valve closure having an interior, central bore. A lower ball carrying assembly defines a first annular, sealing seat surface in contact with and adapted to seal with the exterior of the valve closure. The first seat surface defines a first through hole. An upper assembly defines a second annular seat surface in contact with the exterior of the valve closure. The second seat surface defines a second through hole. The second through hole is shaped differently from the first through hole in that it at least partially overlaps with the central bore while the first through hole is sealed from the central bore.