| 摘要 |
An operating string (OS) has upper and lower wipers (45), (26) with external seals thereon releasably connected to the operating string (OS). A lock arrangement (98), (210d), (230), (234), (235), (91b) prevents premature release of the upper (45) and/or lower (26) wiper by mechanical force, but is responsive to fluid pressure in the operating string (OS) to first release the lower wiper (26) from the operating string (OS) prior to release of the upper wiper (45). The upper wiper (45) cannot be released from the operating string (OS) until the lower wiper (26) has released from the operating string (OS). Seals (210), (217), (218), (45a), (45b), (45c), (45d), (231), (232) are provided to close off communication between the operating string bore (21) and the external wiper seals (29), (46b') to confine the pressure present in the operating string(OS) in a manner to assure release of the wipers (45), (26) as and when desired and in a sequence as may be desired. The wipers (45), (26) are each connected to the operating string (OS) to accommodate relative rotation therebetween to further reduce the possibility of malfunction or improper functioning in releasing the wipers (45), (26) and to permit the operating string (OS) to be manipulated without releasing the wipers prematurely.
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