Rotary shaft assembly with nested shaft

A rotary shaft assembly for a door, the rotary shaft assembly, together with the door, disposed in a fluid passage through which a fluid flows, the rotary shaft assembly comprising:

• an outer shaft defining a first passage therein;
• and
• a nested shaft defining a second passage therein, located inside the outer shaft, and rotatably supported within the first passage of the outer shaft, wherein
• the outer shaft has an outer opening formed on a circumferential wall of the outer shaft,
• the nested shaft has:
• a nested opening formed on a circumferential wall of the nested shaft;
• and
• an open end at one longitudinal side of the nested shaft along a longitudinal direction of the nested shaft,
• the nested shaft and the outer shaft are configure to be rotatable with respect to each other about a common axis such that a relative rotation angle between the outer shaft and the nested shaft varies between a first angle and a second angle,
• when the relative rotation angle is the first angle, (i) the nested opening overlaps with the outer opening and takes the fluid into the second passage from the fluid passage through the outer opening and (ii) the open end discharges the fluid from the second passage, and
• when the relative rotation angle is the second angle, the outer opening and the nested opening are offset from each other and block a flow of the fluid from the fluid passage to the second passage.