High pressure fuel pump for a fuel system of an internal combustion engine

The pump assembly (10) has a shaft (38) with an eccentric (40) driving pistons (42-46) in cylinders (48-52). Each piston has an inlet valve (54-58) and an outlet valve (60-64). Two cylinders 180 degrees out of phase draw low-pressure fuel (18) from a first pipe junction (80) and deliver high-pressure fuel to a second junction point (74). Fuel passes through a non-return valve (76) to a high-pressure reservoir (24). A third cylinder is 90 degrees out of phase with and directly delivers fuel to the inlet line (66) for the high-pressure reservoir. The system contains a pressure sensor (32) and a control valve (78) which may release high-pressure fuel back from the second junction point to the first.