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Brief introduction：Normally Closed Valve mostly work with hydraulic packer which set by differential pressure.
After operation and would to pull out of packer, drop ball to increase pressure for opening circulating port, make sure to balance pressure above & below packer when pulling out of completion string tools, could start directing & reversing operation.
Ⅱ type of normally closed valve could shoot ball valve to bottom, inject heavy crude oil by annulus, mix with down-hole back liquid and return to surface from string tool. |
