Pump unit and method of operating the same

A method of operating a pump unit, the method comprising the following steps:

• (a) displacing an inlet valve member with an armature to an open position which is apart from a valve seat to establish fluid communication between a low pressure fuel supply line and a pumping chamber through a bore in the inlet valve member;
• (b) latching the inlet valve member in said open position using a means for latching the inlet valve member which comprises a solenoid which circumferentially surrounds the inlet valve member when the inlet valve member is in the closed position, wherein latching the inlet valve member includes applying current to the solenoid which magnetically attracts the armature and latches the inlet valve member in said open position;
• (c) initiating a plunger pumping stroke within the pumping chamber when the inlet valve member is latched in said open position;
• and
• (d) unlatching the inlet valve member during the plunger pumping stroke to displace the inlet valve member to a closed position which is seated with the valve seat to inhibit fluid communication between the low pressure fuel supply line and the pumping chamber and to establish fluid communication between the pumping chamber and an outlet valve through the bore in the inlet valve member, wherein unlatching the inlet valve member includes terminating current to the solenoid which stops magnetic attraction of the armature and unlatches the inlet valve member.