Ink supply system and method of operating an ink supply system of an inkjet printer

A method of operating an ink supply system for an inkjet printer comprising a print head arrangement incorporating several print heads with one or more nozzles for at least one color, which print heads are connected via first connecting lines to a supply tank connected to an intermediate tank via a filling line with a first interconnected conveyor device and filter arrangement, wherein each print head is connected via a respective second connecting line to a common return tank, and with a pressure control device connected to the return tank for maintaining a pressure difference between the pressure in the supply tank and the pressure in the return tank to control a flow of ink from the supply tank via the flow passages of the print heads connected in parallel to the return tank, wherein the return tank is connected to the supply tank via a return line, wherein the pressure difference between the pressure in the return tank and the pressure in the supply tank is intermittently varied by the pressure control device so that the pressure difference controls an ink flow from the return tank to the supply tank through the print head and such that the flow direction of the ink through the at least one print head is reversed to achieve cleaning, said method comprising:

• feeding the ink from a supply tank to each of the print heads separately via respective separate first connecting lines in printing mode and
• circulating the ink from the print heads respectively via separate second connecting lines to a return tank and back to the supply tank again,
• wherein during printing mode, the ink is fed directly from the return tank to the supply tank and an amount of the ink in the supply tank is maintained via the filling line during printing operation.