Patent ID: 8444109

Claim:
A blowout preventer for an oil or gas well, comprising: a blowout preventer body having an opening disposed therethrough for a tubular product to be inserted through the opening and having at least a first guideway formed at an angle to a centerline of the opening; a first ram slidably coupled to the blowout preventer body along the first guideway formed in the body; and a first actuator coupled to the first ram and adapted to move the first ram along the first guideway in a lateral direction between an open position and a closed position, the first actuator comprising: an actuator body having a sleeve disposed at an angle to a centerline of the opening sleeve formed therein; an actuator piston having an actuator piston head slidably disposed at least partially within the sleeve and sealingly engaged with the sleeve, a first end of the actuator piston being coupled to the first ram, and a second end of the actuator piston being coupled to a threaded shaft having threads formed on the shaft; the actuator piston head dividing the sleeve into an inward chamber within the sleeve in a direction toward the centerline of the opening and an outward chamber within the sleeve in a direction away from the centerline of the opening; a locking nut rotatable relative to the actuator body, the locking nut having corresponding threads adapted to engage the threads on the threaded shaft of the actuator piston and adapted to allow the threaded shaft to move laterally with the actuator piston head as the locking nut rotates relative to the threaded shaft; and a clutch assembly rotationally fixed relative to the actuator body during inward and outward movement of the ram and selectively coupled with the locking nut and adapted to restrain rotation of the locking nut, the clutch assembly comprising: a clutch plate having a gripping surface disposed toward the locking nut; a bias assembly comprising a bias member and a bias member retainer coupled to the bias member, the bias assembly adapted to bias the clutch plate toward the locking nut; and a clutch piston slidably coupled with the actuator body and adapted to selectively engage the clutch plate with the locking nut, the clutch piston having a first portion with a first pressure area and a second portion with a second pressure area, a difference between the first pressure area and the second pressure area forming a differential pressure area, the first pressure area being sealed from the second pressure area, the first pressure area being fluidicly coupled to a port to provide fluid pressure to the first pressure area independent of fluid pressure on the second pressure area.