Patent ID: 7887302

Claim:
A variable flow pump, comprising: (a) a housing including an inlet chamber and an outlet chamber interconnected by a main bore; (b) a non-rotating cylinder block with first and second ends disposed in the main bore, the cylinder block including: (i) a central bore disposed in fluid communication with the inlet chamber; (ii) a plurality of cylinder bores arrayed around the central bore; (iii) a plurality of first feed passages interconnecting the inlet chamber and the cylinder bores, the first feed passages defining a bypass flowpath between the cylinder bores and the inlet chamber; and (iv) at least one check valve directly connected to the second end which permits fluid flow from the cylinder bores to the discharge chamber but prevents flow in the opposite direction; (d) a plurality of pistons disposed in the bores; (e) a shaft mechanically coupled to the pistons so as to cause the pistons to reciprocate through an axial pump stroke between predetermined fill and discharge positions, when the shaft is rotated; and (f) a mechanism coupled to the cylinder block which is adapted to selectively axially position the cylinder block within the housing, so as to vary the size of the bypass flowpath.