Abstract: A high pressure piston pump includes a housing having a low pressure fuel inlet and a high pressure fuel outlet; at least two pistons disposed in the housing; a driveshaft for supplying power to drive the at least two pistons; and a bypass valve fluidly connected to at least one of the at least two pistons to deactivate the at least one piston. A method of varying the flow output of a high pressure piston pump having at least two pistons includes deactivating at least one of the two pistons by directing fluid displaced by the at least one piston to a bypass valve.

Abstract: A fuel delivery system 10 includes a fuel rail 22 to supply fuel to at least one fuel injector 26, a high pressure fuel pump 20 to provide fuel to the fuel rail 22, a fuel regulator 28 to regulate fuel pressure at the fuel rail 22, and flow restriction structure 30, 32 disposed in a fuel return line 34 between the fuel regulator 28 and the high pressure fuel pump 20. The flow restriction structure 30, 32 is constructed and arranged to substantially prevent bubbles from reaching the high pressure fuel pump 20 when the high pressure fuel pump is providing fuel in a certain flow range to the fuel rail 22. The flow restriction structure defines at least one flow restricting orifice.