| 摘要 |
A downhole tool (20) comprises a body (22), a tool function member (28, 30) axially movable relative to the body (22) from an initial position to an operative position, a first spring (32) responsive to a first fluid pressure force for permitting movement of the tool function member (28) from the initial position to an intermediate position; and a second spring (33) responsive to a higher second fluid pressure force for selectively permitting movement of the tool function member (30) to the operative position. The tool function member may be in one or two parts and may include a bypass sleeve (30).
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