API SPEC 16F pdf download.Specification for Marine Drilling Riser Equipment 3 Definitions and Abbreviations 3.1 accumulator (BOP): A pressure vessel charged with gas over liquid and used to store hydraulic fluid under pressure for operation of blowout preventers. 3.2 accumulator (riser tensioner): A pressure vessel charged with gas over liquid that is pressurized on the gas side from the tensioner...