A detailed answer will depend on make and construction of the valve, operation element for the valve (lever gear or actuator), and sealing (metal or soft) and detailed sealing construction.a) The disc at thight closed BFL valves, also double and triple offset BFL valves, has usually some slight variation in position from 100% 90 degrees, and some slight adjustment possibillities in closing position. This to allow correct sealing, but not too high loosening torque. This adjustment has to be done manually, and endstops corrected accordingly. (Exception is perhaps direct leveroperated smaller valves where the lever is positioned normally by a thoothed plate)b) Even if offset valves do not get stuck as easily as centric valves, it can and will happen if the disc is forced too hard into the seat.c) Most common if disc is 'stuck' is that the disc position is to much forced in closed direction, and/or has remained too long in closed position. If electrical actuator: check limit switches position and that actuator stops on limit switches and that actuator turns in the right direction (phase connections correct). If pneumatic actuator check that actuator has endstops and adjust endstops correctly. Same for manual gear. Check valve seat and sealings for damage.d) Disc can be turned in wrong direction when open but not more than about 90 degrees from fully open and will not seal.

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