Lid construction for breathing apparatus

A breathing assistance apparatus comprising:

• a main body comprising a cavity;
• a lid rotatable between an opened position and a closed position, the lid enclosing the cavity when in the closed position;
• at least one of the lid and the main body comprising a post, and another of the lid and the main body comprising a corresponding support, the support comprising a recess, the recess being able to receive at least a portion of the post, the recess comprising a mouth and an end surface, the end surface being forward of the mouth, the recess comprising an axis, the axis being defined between the mouth and the end surface, the mouth receiving the post when the lid is in a detached open position;
• at least one of the lid and the main body comprising a cam structure, and another of the lid and the main body comprising a guide structure, the cam structure comprising a first contact point and a second contact point, a sloping surface extending between the first contact point and the second contact point, the cam structure being able to contact the guide structure along the sloping surface as the lid is rotated from the detached open position to an attached closed position;
• and
• the first contact point and the second contact point of the cam structure being separated by a first distance that is parallel to the axis of the recess, the first distance being equal to a second distance, the second distance corresponding to a distance moved by the post along the axis during attachment of the lid to the main body.