Patent ID: 6488260
Filing Date: 2002-12-03
Classification: F16K

Abstract:
A fail safe valve actuator comprising:a housing for mounting on a valve body; a valve stem having one portion adapted to be connected to a valve member of the valve and another portion having an elongated helical groove in its outer surface; means mounting the valve stem in the housing to reciprocate and thereby move the valve member between valve open and valve closed positions; compressible means for urging the valve stem toward one position; means for moving the valve stem to its other position including a ball nut in the housing in engagement with the helical groove on the valve stem and mounted in the housing for rotation relative to the valve stem; an electric motor having an output shaft; means for transmitting the torque from the electric motor to the ball nut to rotate the nut and move the valve stem and valve member to one position including a torque limiting device that will disconnect the electric motor from the ball nut when the torque reaches a pre-selected amount; and electrically powered means for holding the stem and valve member in one position and then releasing the valve stem and valve member for movement by the compressible means to the other position when the electrical power fails, said electrically powered means for holding the stem and valve member in one position including a wrap spring clutch connected to the output shaft of the electric motor that will engage and transmit torque when a solenoid is energized, said wrap spring clutch having a clutch shaft and a centrifugal brake connected to the clutch shaft that will engage and limit the speed of rotation of the clutch shaft when the speed of rotation of the clutch shaft reaches a pre-selected speed of rotation.