A refill unit for refilling an ink storage compartment is provided. The ink storage compartment has an interface for releasably engaging with the refill unit. The interface has valves for controlling ink flows into, and out of, the storage compartment. The refill unit has a body containing a quantity of ink, an ink outlet, and valve actuators for actuating the valves when the refill unit engages the interface, such that the valve actuators actuate the valves in a predetermined sequence.