Fuel pump

A fuel pump (20, Fig. 3) for a fuel injector of an internal combustion engine, the pump comprising a housing 30 provided with an axial bore (32, Fig. 3) and a piston 80 slidably arranged in the bore which defines a lower end through which the piston is received, an upper end opposite the lower end, a side wall 35 that extends between the lower and upper ends, and a compression chamber 40 located that incorporates the upper end of the bore; The housing 30 is provided with an inlet 42 that opens into the compression chamber 40 at the upper end of the bore, and an outlet 44 that opens into the compression chamber 40 at a side wall of the bore; The piston 80 slides reciprocally between a lower position where fuel enters the compression chamber via inlet 42 and an upper position where fuel in the compression chamber 40 is pressurized and expelled via outlet 44; The piston 80 comprises a dilation region 88 at an upper end, and a pressure relief region 90 below the dilation region 88; The pressure relief region 90 comprises a pressure relief means 94, and the dilation region 88 comprises a dilation means 92 configured to dilate in response to a pressure differential between the compression chamber 40 and the pressure relief region 90.