•A large valve used to control wellbore fluids
•In this type of valve, the sealing element resembles a large rubber doughnut that is mechanically squeezed inward to seal on either pipe (drill collars, drillpipe, casing, or tubing) or the openhole.
•The ability to seal on a variety of pipe sizes is one advantage the annular blowout preventer has over ram-type blowout preventers Most blowout preventer (BOP) stacks contain at least one annular BOP at the top of the BOP stack, and one or more ram-type preventers below
•While not considered as reliable in sealing over the openholeas around tubulars, the elastomericsealing doughnut is required by API specifications to seal adequately over the openholeas part of its certification process
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