Patent ID: 8353690

Claim:
A pump comprising: a pair of piston pumps operated about 90° out of phase, each pump comprising a rotating and reciprocating piston disposed in a pump housing, each housing comprising an inlet, an outlet, an interior and a seal, each piston comprising a proximal section coupled to a pump section at a transition section, the proximal section having a first maximum outer diameter, the pump section having a second maximum outer diameter that is greater than the first maximum outer diameter, each pump section comprising a distal recessed section disposed opposite the pump section from the transition section, the pump section extending between the transition section and a distal end of the piston, each housing, piston and seal defining two pump chambers each of which includes a first chamber defined by the distal recessed section and distal end of the pump section of the piston and the housing, and a second chamber defined by the transition section and proximal section of the piston and the housing, wherein each pair of first and second pump chambers being isolated from each other by frictional engagement between the pump section of the piston and the seal, but the first and second pump chambers being in communication with each other via a passageway, and wherein the proximal ends of each piston are linked to a motor so that the pistons are about 90° out of phase with respect to each other.