Single action pneumatic powered spring retractable pump

Claim 1

A downhole pump for pumping well production fluids and the like from a well, said pump comprising: an elongated housing adapted to be inserted in a well, said housing defining an elongated cylindrical bore; a piston reciprocably disposed in said bore and dividing said bore into a power fluid chamber and a production fluid chamber, said piston being movable through an extension stroke and a retraction stroke with respect to said production fluid chamber to discharge and intake fluid with respect to said production fluid chamber, respectively; means forming an inlet port opening into said production fluid chamber for admitting fluid to said production fluid chamber, and means forming a discharge port for conducting fluid out of said production fluid chamber; first valve means for introducing power fluid into said power fluid chamber for causing said piston to move through said production fluid chamber on an extension stroke to deliver a charge of fluid through said discharge port; second valve means for venting power fluid from said power fluid chamber; means operable to be actuated by said piston at a predetermined point on said extension stroke to cause said first valve means to close off communication of power fluid to said power fluid chamber, and to cause said second valve means to vent power fluid from said power fluid chamber; an end block of said housing including a sand trap chamber formed therein; third valve means for venting said sand trap chamber, said third valve means being actuated by means during an extension stroke of said piston to vent fluid from said sand trap chamber; and, said piston including a piston part operable to extend into said sand trap chamber during an extension stroke of said piston to substantially isolate said sand trap chamber from said production fluid chamber and to displace fluid in said sand trap chamber through said third valve means.