Tank, tank unit, and liquid ejection system

A tank capable of supplying a liquid to a liquid ejection head, the tank comprising:

• a liquid containing portion that is capable of containing the liquid;
• a liquid injection portion through which the liquid can be injected into the liquid containing portion;
• and
• an atmospheric air introducing portion through which atmospheric air can be introduced into the liquid containing portion,
• wherein the atmospheric air introducing portion includes a buffer chamber that is capable of containing atmospheric air and an atmospheric air communication path that communicates between the buffer chamber and the liquid containing portion,
• the atmospheric air communication path includes an atmospheric air introducing inlet in an area where the atmospheric air communication path intersects with the liquid containing portion,
• the buffer chamber is provided with a first communication inlet that is connected to the atmospheric air communication path and a second communication inlet through which external atmospheric air can be introduced into the buffer chamber,
• the second communication inlet is disposed at a location where the buffer chamber and an atmospheric air intake portion connected to the buffer chamber intersect,
• when the tank is in a first orientation in which the liquid is injected into the liquid containing portion via the liquid injection portion, the atmospheric air introducing inlet is located on an upper end side of the liquid containing portion,
• the atmospheric air communication path has:
• (i) a first portion that is located at a height position between an upper end portion of the liquid containing portion and a midpoint between the upper end portion of the liquid containing portion and a lower end portion of the liquid containing portion when the tank is in the first orientation;
• (ii) a second portion that is located at a height position between the upper end portion of the liquid containing portion and a midpoint between the upper end portion of the liquid containing portion and a lower end portion of the liquid containing portion when the tank is in a second orientation in which the tank has been rotated by 90° in a predetermined direction from the first orientation;
• and
• (iii) a third portion that is located at a height position between the upper end portion of the liquid containing portion and a midpoint between the upper end portion of the liquid containing portion and a lower end portion of the liquid containing portion when the tank is in a third orientation in which the tank has been rotated by 180° in the predetermined direction from the first orientation, and
• the second communication inlet is located above a lower end portion of the buffer chamber when the tank is in the second orientation and in which the atmospheric air introducing inlet is located on a lower end side, and when the tank is in the third orientation.