| 摘要 |
The disclosure relates to an improved flapper type safety valve for use in subterranean wells wherein the flapper valve is actuated from a horizontal closed position to a vertical open position by contact from a downwardly moving actuating sleeve. The top surface of the valve is elevated so that the bottom edge of the actuating sleeve always contacts the flapper valve at a position maximally spaced from the axis of its pivot mounting, thereby assuring that the opening force applied to the flapper valve has a maximum moment arm in order to overcome any fluid pressure differential existing across the flapper valve.
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