The invention relates to agate valve hydraulic actuator, said actuator comprising a cup shaped sleeve (9) which is operably coupled to an opening or closing element (5) of the gate valve (2), the actuator further comprising a movable primary piston (13) arranged within a primary cylinder (12) arranged at the inside of the cup-shaped sleeve (9), said primary piston (13) being con figured to move the sleeve (9) and hence said opening and closing element (5) towards an open or closed position of the gate valve (2) by a force applied to the primary piston (13). The hydraulic actuator is distinctive in that it further comprising a movable secondary piston (11) arranged within a secondary cylinder (10) arranged at the inside of the cup shaped sleeve (9), said secondary piston (11) being configured to move the sleeve (9) to the same position of the gate valve (2) as the primary piston by a force applied to the secondary piston in case of failure of the primary piston (13), said primary piston (13) and secondary piston (11) are independently operable of each other.