A valve device for a medical fluid line system includes a main body, the main body having a first fluid passage and a second fluid passage, each fluid passage of the first and second fluid passages extending between an inlet side and an outlet side of the main body. The main body has a first wall portion and a second wall portion which are each elastically displaceable, under an effect of fluid pressure, relative to a substantially dimensionally stable web portion of the main body. Each wall portion of the first and second wall portions is arranged on the web portion, forming one of the first and second fluid passages, in such a way that the first fluid passage is substantially uninfluenced by a fluid-pressure-induced deformation of the second wall portion, and the second fluid passage is substantially uninfluenced by a fluid-pressure-induced deformation of the first wall portion.