| 摘要 |
The present invention has been contemplated to meet the above described needs. In a broad aspect, the invention may include a subsurface safety valve for controlling a fluid flow through a well conduit comprising a housing having a bore and disposed within an annulus defined by the space between the well conduit and the housing, a valve closure member movable between an open position and a closed position, and adapted to restrict the fluid flow through the bore when in the closed position, a flow tube moveably disposed within the housing and adapted to shift the valve closure member between its open and closed positions, a primary piston member in operative communication with the flow tube and a secondary piston member in operative communication with the flow tube.
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