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 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 the effect of fluid pressure, relative to a substantially dimensionally stable web portion of the main body. Each wall portion is arranged on the web portion, forming one of the 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.
