 1946 Blowout preventer (annular)

An annular blowout preventer is a large valve that uses a wedge to seal off a wellhead.It has a donut-like rubber seal, known as an elastomeric packing unit, reinforced with steel ribs.During drilling or well interventions, the valve may be closed if overpressure from an underground zone causes formation fluids such as oil or natural gas to enter the wellbore and threaten the rig.