Fuel injection system, fuel pump and plunger

A fuel pump 14 and injection system 10 for providing a variable feed rate are disclosed. The pump comprises a discharge valve (in carrier 20) with a predetermined opening pressure. The pump is configured so that at the minimum feed rate fuel is pressurised to a pressure higher than the opening pressure of the valve. The minimum feed rate may relate to a non-injection mode of a system which incorporates an injection nozzle 18. Control of the feed rate may be achieved using a piston/plunger with a controlling structure comprising sealing surfaces that sequentially block a fuel port. The injection valve 18 may be configured with a higher opening pressure than the pressure required to open the discharge valve. The arrangement allows the high pressure pipe 16 to remain pressurised when no injection is taking place and so minimises cavitation. The arrangement finds particular use in dual fuel systems. A plunger for a fuel pump is also disclosed.