| 摘要 |
A landing nipple, adaptable to be made up in a tubing string having a sliding sleeve disposed in its bore for selectively providing communication of balance and control pressure fluid to the nipple bore. When the sleeve is shifted to its first, upper position, balance fluid is conducted via the nipple to a tubing retrievable safety valve placed in the tubing string below the nipple. In the event the tubing retrievable safety valve is taken out of service, a secondary safety valve can be landed in the nipple, the sleeve shifted to its downward, second position, opening sleeve ports for conducting control and balance fluids to the landed, secondary safety valve. The nipple has a failed closed safety system provided by the novel arrangement of nipple entry ports for balance and control fluid, in that the control fluid entry port is in between two balance fluid ports and their seals, so that failure of the pressure seal exposed to tubing pressure causes tubing pressure to enter the balance pressure system closing the tubing retrievable or secondary safety valve, whichever is presently in service.
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