Axial flow fan unit

A serially connected axial flow fan unit, comprising:

• a first axial flow fan including a first impeller and a first housing;
• and
• a second axial flow fan including a second impeller and a second housing;
• the first housing including at a first end portion thereof a first axial locking mechanism and a first unlocking mechanism;
• and
• the second housing including at a second end portion thereof a second axial locking mechanism arranged to engage with the first axial locking mechanism and a second unlocking mechanism arranged to engage with the first unlocking mechanism;
• wherein
• the first axial locking mechanism and the second axial locking mechanism are configured to be locked against each other through their movement along an axis of the axial flow fan unit;
• the first unlocking mechanism and the second unlocking mechanism are configured to unlock the first housing and the second housing with a twisting force equal to or greater than a predetermined value when the first housing and the second housing are twisted relative to each other in a specified direction;
• and
• when the first end portion and the second end portion are brought into contact with each other, the first axial locking mechanism and the second axial locking mechanism are locked against each other and the first unlocking mechanism and the second unlocking mechanism engage with each other.