| 摘要 |
<p>A downhole tool has a tubular valve housing (102,104,106,108), a valve closure member movable (132) between an open and a closed position, an axially movable opening flow tube (124,130) for opening the valve closure member (132). Hydraulic pressure from a control line (114) is used to move a first piston (118), which in turn moves the axially movable flow tube (124,130) through the closure member (132). A balance line (116) can be used to provide a hydrostatic pressure against a second piston (120). The downhole tool can be used as a subsurface safety valve. <IMAGE> <IMAGE> <IMAGE></p> |
