The annular BOP is named because of its well sealing rubber core annular element. Well sealing, in the control system to control the pressure, an annular rubber core was forced to hole center, surrounded by drill, so as to realize the well sealing, effectively prevent blowout accidents, safety construction, and it is often ram blowout preventer supporting the use of.

Annular blowout preventer functions:

1, when there is no drill hole, annular preventer for closed wellhead (Feng Ling).

2, when the drill tools in hole, casing, wire rope, cable, can be closed wellhead.

3, for different size of wellhead suspension, different sections of the drill can achieve a good seal.

4,Butt welded drill pipe is  with 18 ° slope joints in closed, forcibly tripping.