Patent ID: 7927083

Claim:
A pump adapted to be used in a tubing in a well, the pump comprising: a piston assembly reciprocably engaged in a cylinder assembly, the piston assembly comprising a first piston coupled to a second piston, the second piston having a cross-sectional area larger than a cross-sectional area of the first piston, a pumping chamber being defined by the piston assembly and the cylinder assembly, the cylinder assembly connectable to the tubing such that the first piston is in fluid communication with a bore of the tubing and the pumping chamber is in fluid communication with the bore of the tubing by way of a first one-way valve oriented to permit fluid to flow from the pumping chamber into the bore of the tubing and a first means for biasing the piston assembly in a first direction, the first means for biasing the piston assembly in a first direction extending between the piston assembly and an anchor point located outward of the piston assembly, wherein the piston assembly is movable in a second direction, which is opposite the first direction, by increasing a fluid pressure in the bore of the tubing against the first piston, the pressure being increased by introducing a first volume of fluid into a column of fluid in the bore of the tubing, and wherein a second volume of fluid is expelled from the pumping chamber into and becomes part of the column of fluid in the bore of the tubing when the piston assembly moves in the first direction, the second volume of fluid being larger than the first volume of fluid.