Liquid supply unit and liquid injection device

A liquid supply unit for supplying predetermined liquid from a liquid storage container storing the liquid to a liquid injection head for injecting the liquid, comprising:

• a pressure chamber capable of storing the liquid;
• a first supply passage allowing communication between the liquid storage container and the pressure chamber;
• a second supply passage allowing communication between the liquid injection head and the pressure chamber;
• a bypass supply passage having an upstream end in a liquid supply direction connected to the first supply passage and a downstream end joining the second supply passage;
• and
• a pressurizing mechanism arranged in the bypass supply passage and configured to pressurize the liquid flowing in the bypass supply passage;
• a valve mechanism configured to operate according to a pressure state of the pressure chamber;
• wherein:
• the pressure chamber and the second supply passage are maintained at a predetermined supply negative pressure when the liquid is supplied to the liquid injection head;
• a part of a wall portion defining the pressure chamber is formed by a flexible film member;
• and
• the valve mechanism prohibits the inflow of the liquid from the first supply passage in a first state where the pressure chamber is within the range of the supply negative pressure, allows the inflow of the liquid from the first supply passage in a second state where the pressure chamber is at a pressure lower than the supply negative pressure, and releases the pressure in the pressure chamber in a third state where the pressure chamber is at a pressure higher than the supply negative pressure by a predetermined value, the pressure in the third state being generated by the pressurizing mechanism.