Patent ID: 8453729

Claim:
A hydraulic actuator for a setting assembly of a tool for use in oil and gas wells, said hydraulic actuator comprising: a. a cylindrical mandrel; b. an annular stationary sealing member connected to said mandrel; c. a hydraulic cylinder slidably supported on said mandrel and said stationary sealing member, said cylinder being releasably fixed in position relative to said mandrel; d. said stationary sealing member dividing the interior of said cylinder into a bottom hydraulic chamber and a top hydraulic chamber; e. an inlet port providing fluid communication into said bottom hydraulic chamber; f. an outlet port providing fluid communication into said top hydraulic chamber; g. an annular balance piston slidably supported within said top hydraulic chamber between said outlet port and said stationary sealing member, said balance piston comprising a passageway extending axially through said piston wherein fluid communication between the sides of said balance piston through said passageway is controlled by a normally shut valve; h. whereby, when said cylinder is fixed in position on said mandrel, said balance piston is capable of sliding in response to a differential in hydrostatic pressure between said outlet port and said top hydraulic chamber.