Over-pressure relief valve in a fuel system

A fuel system (10) arranged to deliver fuel at high pressure to a fuel injector through a high pressure fuel line (42, 44) defined, at least in part, within first and second housing parts (46, 40) of a pressure relief valve arrangement. The first and second housing parts (46, 40) define first and second separable valve surfaces respectively. A clamping means (46) is provided for applying a clamping load to the first and second housing parts (46, 40) so as to urge first and second valve surfaces respectively thereof into substantially sealing engagement. The clamping means is arranged to permit separation of the first and second valve surfaces in the event that fuel pressure within the high pressure fuel line (42, 44) exceeds a predetermined amount, thereby to permit fuel within the high pressure fuel line (42, 44) to flow to a region (62) of relatively low pressure to relieve fuel pressure within the high pressure fuel line.