| 摘要 |
A retrievable subsurface safety valve positioned in a well conduit is actuated to close by a predetermined flow rate through the safety valve. A valve member having a sealing surface is moveable by flow to sealingly engage an annular seat in the valve, closing the valve to flow. All forms of the invention safety valve have retrievable variable weight assemblies which releasably lock in the valve member for varying the flow rate at which each valve closes. In two invention forms, the weight assemblies when retrieved from the valve members leave the valve members open for passage of well tools through the valve members. In one invention form, the valve housing has a variable bias for biasing the valve member toward open position and this safety valve may be operated to expend the seat, housing and valve member with or without the variable weight assembly.
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