A ball valve (1), particularly for use in motor vehicle refrigerant circuits, having an actuator (2), a shaft (3) including a shaft bearing (5), a ball (4) including a ball passage (16), and a valve housing (13). A fluid shaft seal (8) is arranged in the shaft bearing (5) between an upper shaft seal (6) and a lower shaft seal (7), wherein the fluid shaft seal (8) is formed by a cavity (18) in which a sealing fluid is provided, and that the sealing fluid is in contact with the shaft (3) in a sealing region (19) such that the sealing fluid has a sealing effect in the axial direction, wherein the cavity (18) is at least partially formed by a diaphragm (11) and is limited on the shaft (3) by the shaft seals (6, 7), and that the diaphragm (11) is formed in such a way that pressure can be applied to the side facing away from the sealing fluid.