A fan (100) has a fan housing (110). The latter has an air entrance opening (120) and an air exit opening (130). It further has a swivel joint arrangement (180) having at least one swivel joint (145, 147, 155, 157, 165, 167, 175, 177) that is arranged on a joint carrier (188; 188′); at least one non-return flap (140, 150, 160, 170) that is journaled rotatably by means of the at least one swivel joint (145, 147, 155, 157, 165, 167, 175, 177) and, in its closed position, at least partly closes off the air exit opening (130); and at least one elastic return member (142, 152, 162, 172) that is associated with the at least one non-return flap (140, 150, 160, 170) and urges it toward its closed position.