22 and the male connector 24 and the slot membrane 1 with for example four or six radially extending slots valve 20 has a rotary ring 25 held rotatably on housing 22 24 and a spreader 26 mounted displaceably in the housing the spreader 26 can be pushed into the range of action of the slot membrane 1 or of the lamella area 3 such that the membrane lamellae 3 a 3 d of the slot membrane are permanently opened in the direction of the patient in order to thus release the flow center in the interior of the valve and not to represent a relevant flow resistance spreader 26 has two holding noses 27 which open through the housing between the male and female tube connectors 22 24 into the oblique path 28 of the rotary ring 25 the rotary ring 25 has besides the oblique path 28 an annular groove 29 into which snaps a bead 30 of the housing the rotary ring 25 is axially fixed at the housing hereby when rotating the rotary ring spreader 26 is axially displaced over the oblique path 28 and can thus be brought optionally into a position close to the y piece respirator side where the spreader does not mesh with.