The invention concerns a valve actuator (1) comprising a housing (2) and a nut and screw arrangement. A first portion (5) of the nut and screw arrangement is operated by an electric motor (7), which is fixed to the housing (2). A means (8) is in contact with a second portion (6) of the nut and screw arrangement, and a resilient means (9) is acting between the means (8) and the housing (2). A relative rotation between the threaded nut (3) and the threaded screw (4) leads to a translation of the means (8) and an energizing or de-energizing of the resilient means (9). A locking means (10) locks the resilient means (9) in an energized state by locking the relative rotation of the nut and screw arrangement. When the locking means (10) are released, the resilient means (9), when de-energizing, acts on the means (8), leading to a translation of the means (8).