Patent ID: 7921922

Claim:
A formation saver sub, comprising: a tubular body including an upper section, a middle section, a lower section, an outer surface, and an inner surface, said upper section of said tubular body is adapted for connection to a well tubing, said well tubing including a well tubing bore; a mandrel including an upper section, a middle section, a lower section, an outer surface and an inner surface defining a mandrel bore, said mandrel being positioned interior of said body, said upper section of said mandrel is adapted for connection to said well tubing; a piston including an upper section, a middle section, a lower section, an outer surface, and an inner surface, said piston positioned between said inner surface of said body and said outer surface of said mandrel, said piston including a fluid chamber; wherein said mandrel includes a passage for fluid communication between said mandrel bore and said fluid chamber of said piston; a seat including an upper section, a middle section, a lower section, an outer surface, and an inner surface defining a seat bore, said seat releasably positioned in said mandrel bore, said upper section of said seat adapted to receive a plug; wherein said piston is actuated in a first direction in response to an increase in a fluid pressure, said actuation in said first direction maintains said positioning of said seat in said mandrel bore; and wherein said piston is actuated in a second direction in response to a bleed off of said fluid pressure, said actuation in said second direction releases said seat from said mandrel bore; a sleeve including an upper section, a middle section, a lower section an outer surface and an inner surface, said sleeve connected to said piston, said sleeve positioned between said inner surface of said body and said outer surface of said mandrel; a shear means detachably affixing said sleeve to said mandrel; a spring means positioned between said inner surface of said body and said outer surface of said mandrel, said spring means being in cooperative engagement with said piston; wherein said actuation of said piston in said first direction shears said shear means thereby detaching said sleeve from said mandrel and moving said piston and sleeve sward to compress said spring means; wherein said actuation of said piston in said second direction includes an expansion of said spring means to move said piston and sleeve downward to a position that results in said release of said seat from said mandrel bore; and at least one retractable dog supported in said mandrel, said dog including a first end and a second end, said first end of said dog releasably engaging said seat to position said seat in said mandrel bore prior to said actuation of said piston in said second direction; and wherein said actuation of said piston in said second direction causes said first end of said dog to disengage from said seat to release said seat from said mandrel bore to eliminate obstruction of said well tubing bore.