Patent ID: 7779918

Claim:
A control device for sealing a wellbore, the device having a generally cylindrical housing, the housing having a cylindrical throughbore with a central axis for receiving a workover string, the housing including: at least one moveable ram, at least one moveable piston, at least one linkage mechanism comprising a first linkage member and a second linkage member, the first linkage member having a first end and a second end, the first end being pivotally coupled to the at least one piston and the second end being pivotally coupled to the at least one ram, the pivotal coupling is achieved by using pin joints, the second linkage member having a first end and a second end, the first end being pivotally coupled to the first linkage member and the second end being pivotally coupled to the housing and being permanently fixed axially relative to the housing, the linkage mechanism being arranged so that in response to movement of the at least one piston parallel to the axis of the throughbore towards the at least one ram, the linkage mechanism forces the at least one ram to move substantially orthogonally to the axis of the throughbore across the throughbore, and wherein the second end of the second linkage member is coupled to the housing by a second linkage-second end pin joint, the second linkage-second end pin joint and the first linkage-first end pin joint being located on an axis parallel to the axis of the throughbore, and the second linkage-second end pin joint and the first linkage-second end pin joint being located on an axis located substantially orthogonal to the axis of the throughbore.