| 摘要 |
<p>In accordance with an illustrative embodiment of the present invention, a subsurface safety valve assembly includes a dome precharged with a set reference pressure that tends to close the valve, and means responsive to both ambient pressure and to the pressure of a control fluid for holding the valve open under normal conditions, a decrease in either control fluid pressure or tubing pressure, or both, enabling the dome pressure to cause the valve to automatically close and shut-in the well. The valve does not employ a coil spring to cause closure, which permits installation at great depths in a well, and a narrow spread between valve opening and closing pressures.</p> |
