Ink reservoir with automatic air vent

1. An ink reservoir for a printer with an inkjet printhead, the ink reservoir comprising:

a housing for storing a quantity of ink;

an air inlet valve having a ball biased against an aperture of the air inlet valve for sealing an interior of the housing from atmosphere;

an ink outlet valve having a circular valve seat and a ball for sealing against the valve seat; and

a valve actuator having a sliding shaft extending between the ink outlet valve and the air inlet valve, wherein

the valve actuator opens the air inlet valve in response to the ink outlet valve opening to establish fluid communication with the inkjet printhead, and

the ball in the ink outlet valve is adapted to engage one end of the sliding shaft to slide the shaft towards the air inlet valve, whereat the other end of the shaft engages the ball of the air inlet valve against the bias applied thereon.

2. An ink reservoir according to claim 1 , wherein the sliding shaft is biased into engagement with the ball of the ink outlet valve, to bias the ball against the valve seat.

3. An ink reservoir according to claim 1 , wherein the reservoir is a removable cartridge and the ball in the ink outlet valve engages a formation on the printer that unseats the ball from the valve seat as the cartridge is installed in the printer.