US Patent 9133680 Wellbore control device

A wellbore control device for use in a blow out preventer is described. The control device comprising a housing defining a throughbore, a gate, the gate being movable between a throughbore open position and a throughbore closed position, a first stem attached to the gate and a second stem releasably engageable with the gate, the first and second stems being arranged such that a portion of each stem is exposed to an internal housing pressure and a portion of each stem is exposed to an external housing pressure. When the internal pressure is greater than the external pressure, the pressure differential results in a force being applied to the gate to move the gate to, or retain the gate in, the throughbore closed position.