Patent ID: 8579610

Claim:
A downhole pump, comprising: a) a barrel having a first one-way valve; b) a plunger having first and second ends, with a passage that extends between the first and second ends and a counterbore in each of the first and second ends, the plunger second end located between the plunger first end and the first valve, each of the counterbores having a threaded portion and an unthreaded portion, with the respective threaded portion extending from the respective first and second end and located between the respective first and second end and the respective unthreaded portion, each of the first and second ends of the plunger being blunt and non-tapered the plunger reciprocating in the barrel between an upstroke and a downstroke; c) a second one-way valve located in the counterbore of the second end, the second valve comprising an insert with a ball located in the insert, a seat adjacent to the insert, and a seat plug having a seat end and an exterior end, the seat end of the seat plug being in contact with the seat, the seat plug having a channel therein with a pressure seal in the channel, the seat plug removably coupled to the threaded portion of the second end counterbore so as to form a box end of the plunger, the insert, the seat and the seat plug located inside of the plunger passage with the insert located in the unthreaded portion of the second end counterbore, the exterior end of the seat plug being substantially coplanar with the second end of the plunger so as to permit the seat to be located close to the first one-way valve of the barrel when the plunger is at a bottom of the downstroke, the seat plug removable from the plunger through the second end of the plunger; d) the plunger being reversible so that the second one-way valve can be located in the first end counterbore of the plunger when the plunger first end is located between the plunger second end and the first one-way valve.