ELECTRICALLY DRIVEN ACTUATOR WITH FAILSAFE FEATURE

摘要

A valve actuator preferably driven by an electric motor is disclosed. The valve actuator is useful with surface safety valves and uses power input from an electric motor to position the valve in its normal position. A mechanism is pro vided to allow the valve to shift positions to a fallsafe position upon failure of ele ctrical power to the motor connected to the actuator. A screw drive is provided with th e motor, with a latch mechanism holding a nut against rotation. The nut can advan ce longitudinally upon rotation of the drive to move a valve stem. Upon failure of electrical power, the latch mechanism releases the nut form a coupling in the actuator which is connected to the valve stem, and the main return springs in th e actuator allow the nut to rotate with respect to the screw drive so that the val ve can assume its failed position. Normal applications allow the valve to fail closed; however, the valve can be configured so that failure results in opening of the v alve if the application requires it.