The invention relates to a respiratory flow sensor (11) comprising a flow tube (12) which has a flow channel (13) and tube connections for tubes at the free ends (15, 17) of the flow tube, a cover flap (32) which is arranged in the flow channel (13) and divides the flow channel (13) into a first flow channel section (18) and a second flow channel section (19), and comprising connections (22, 23) which open into the flow channel (13) on both sides of the cover flap (32) and which are used to decrease the pressure difference generated by the cover flap (32). A drainage device (41) which comprises drain grooves (42, 43) is provided in the flow channel (13), and the cover flap (32) has a hinge region which is formed by a first slot and a second H-shaped slot.
