Pump unit

The present application relates to a pump unit (1) for a fuel injection system. The pump unit (1) has a low pressure fuel supply line (11) and a high pressure fuel outlet (13). A pumping chamber (5) having a plunger (15) is operable to perform a pumping cycle comprising a pumping stroke and a filling stroke. The pump unit (1) also includes an inlet valve (7) having an inlet valve member (19) movable between an open position for permitting the supply of fuel to the pumping chamber (5) from the low pressure fuel supply line (11) and a closed position for inhibiting the supply of fuel from the pumping chamber (5) to the low pressure supply line (11). An outlet valve (9) is provided in the high pressure fuel outlet (13). The pump unit (1) also includes a means (39) for latching the inlet valve member (19) in its open position. The present application also relates to a method of operating a pump unit (1).