Patent ID: 7458309

Claim:
A reciprocating pump, comprising: a first pressure chamber at least partially defined by a first flexible member; a second pressure chamber opposing the first pressure chamber and at least partially defined by a second flexible member; a shaft member extending between the first flexible member and the second flexible member; a first shift piston positioned proximate to the first flexible member on a side thereof opposite the shaft member, wherein the first shift piston comprises an elongated member including a first end portion having a first cross-sectional area and a substantially central portion having a second cross-sectional area greater than the first cross-sectional area; and a second shift piston positioned proximate to the second flexible member on a side thereof opposite the shaft member, wherein the second shift piston comprises an elongated member including a first end portion having a first cross-sectional area and a substantially central portion having a second cross-sectional area greater than the first cross-sectional area.