Low pressure responsive downhole tool with floating shoe retarding means

摘要

An annulus pressure responsive downhole tool includes a housing having a power piston slidably disposed therein. First and second pressure conducting passages communicate a well annulus with first and second sides of the power piston. A retarding device is disposed in the second pressure conducting passage for delaying communication of a sufficient portion of an increase in well annulus pressure to the second side of the power piston for a sufficient time to allow a pressure differential across the power piston to move the power piston from a first position to a second position relative to the housing. The retarding device is an annular floating shoe having a large number of O-rings frictionally engaging inner and outer tubular members of said housing. A pressure relief valve is communicated with the second pressure conducting passage between the power piston and the retarding device for relieving from the second pressure conducting passage a volume of fluid sufficient to permit the power piston to travel to its second position. A spring biased pin disposed in the housing engages an indentation in an actuating mandrel attached to said power piston to releasably hold the power piston in its second position.