| 摘要 |
A subsurface safety valve (SSV) comprises a valve closure member such as a flapper valve and a flow tube adapted to move the flapper valve between open and closed positions. The SSV also comprises primary 112 and secondary pistons, both of which are in operative communication with the flow tube and which may be capable of independent operation via primary 110 and secondary 126 hydraulic circuits. The secondary piston may further comprise upper 128 and lower 130 pistons, movement of the upper 128 piston being limited by a locking device 134. |
