Device placed at top of the riser string that provides flow control of the production and/or annulus bores during production.
Source: API Standard 2RD, Dynamic Risers for Floating Production Systems, Second Edition, September 2013. Global Standards
Device which provides flow control of the production and/or annulus bores during both tubing hanger installation and subsea tree installation/workover operations. NOTE It can also have provisions to support the mass of the C/WO riser system.
Source: API RP 17G, Recommended Practice for Completion/Workover Risers, Second Edition, July 2006 (Reaffirmed April 2011). Global Standards