Ink delivery system for inkjet printer

A thermal ink jet printer, comprising:

• a print head having
• an ink ejector including a cavity suitable for containing ink and a resistor adjacent the cavity to heat the ink in the cavity upon passage of an electrical current through the resistor,
• an ink flow channel through which ink can flow, the ink flow channel being disposed such that ink flowing therethrough is heated by heat produced by the ink ejector, and
• a capillary channel communicating at one end with the ink flow channel and at the other end with the cavity of the ink ejector;
• a pump that pumps ink simultaneously with the operation of the ink ejector during printing operation of the ink jet printer;
• a stationary ink reservoir that holds a supply of ink, the ink reservoir being located at a level below the cavity in the ink ejector;
• an ink supply tube extending from the high pressure side of the pump to one end of the ink flow channel;
• a first ink return tube extending from the other end of the ink flow channel to the reservoir;
• and
• a second ink return tube extending from the reservoir to the inlet side of the pump.

A process for supplying ink to an ink jet printer, comprising the steps of:

• supplying an ink jet print head, from which droplets of ink may be ejected, the ink jet print head having an ink flow channel therethrough;
• pumping ink through the ink flow channel of the print head to provide ink for ejection and to cool the print head, as the print head operates during printing, at a flow rate greater than required to supply the printing requirements of the print head, while maintaining the pressure of the ink in the ink flow channel of the ink jet print head below atmospheric pressure;
• and
• withdrawing a portion of the ink flowing through the ink flow channel for ejection from the print head.