Importance

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Abstract

An operating string has upper and lower wipers with external seals thereon releasably connected to the operating string. A lock arrangement prevents premature release of the upper and/or lower wiper by mechanical force, but is responsive to fluid pressure in the operating string to first release the lower wiper from the operating string prior to release of the upper wiper. The upper wiper cannot be released from the operating string until the lower wiper has released from the operating string. Seals are provided to close off communication between the operating string bore and the external wiper seals to confine the pressure present in the operating string in a manner to assure release of the wipers as and when desired and in a sequence as may be desired. The wipers are each connected to the operating string to accommodate relative rotation therebetween to further reduce the possibility of malfunction or improper functioning in releasing the wipers and to permit the operating string to be manipulated without releasing the wiper prematurely.

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First Claim