Patent ID: 8864103

Claim:
An electrically powered valve actuator connectable to a source of electricity for providing electricity to the valve actuator, the valve actuator comprising: a housing, a threaded nut, a threaded screw extending through the threaded nut, an electric motor fixed to the housing and configured to rotate a first one of the nut and the screw, a contact member in contact with a second one of the nut and the screw, the contact member being axially and rotationally fixed to the second one of the nut and the screw when electricity is provided to the valve actuator and when electricity is not provided to the valve actuator and the contact member being locked against rotation in the housing when electricity is provided to the valve actuator and when electricity is not provided to the valve actuator, a resilient member between the contact member and the housing configured to bias the contact member in a first direction relative to the housing and being shiftable between a first state and a second state, a potential energy of the resilient member being higher in the first state than in the second state, and locking means for locking and unlocking the resilient member, the locking means having a locked condition and an unlocked condition, the locking means being configured to shift automatically to the unlocked condition in response to a stoppage of electricity being provided to the valve actuator, the locking means in the locked condition preventing relative rotation between the threaded nut and the threaded screw and the locking means in the unlocked condition allowing relative rotation between the threaded nut and the threaded screw and allowing the resilient member to shift to the second state, wherein the locking means comprises one of a tooth clutch, a tooth brake, a torque lock, and a friction brake, and wherein the resilient member comprises a spring or a spring washer or a disc spring, and wherein the first one of the nut and the screw comprises the screw and wherein the locking means is configured to prevent relative rotation between the threaded nut and the threaded screw by preventing the threaded screw from rotating relative to the housing.