Valve device for a medical fluid line system, with: - a main body , which is configured to be soft-elastic at least in part, and - a first fluid passage and a second fluid passage which each extend between an inlet side (A) and an outlet side (B) of the main body , - wherein the main body is configured in such a way and the fluid passages are arranged in such a way that, - in the event of a fluid overpressure between the inlet side (A) and the outlet side (B), the first fluid passage is freed by means of a fluid-overpressure-induced elastic deformation of the main body and the second fluid passage is sealed off in a fluid-tight manner, and, - in the event of a fluid underpressure between the inlet side (A) and the outlet side (B), the second fluid passage is freed by means of a fluid-underpressure-induced elastic deformation of the main body and the first fluid passage is sealed off in a fluid-tight manner, and, - in the event of a neutral fluid pressure between the inlet side (A) and the outlet side (B), the fluid passages are sealed off in a fluid-tight manner, wherein the main body has a first wall portion and a second wall portion which are each elastically displaceable, under the effect of a fluid pressure, relative to a substantially dimensionally stable web portion of the main body , characterized in that the wall portions are arranged on mutually opposite side faces of the web portion , thereby each forming one of the fluid passages , and thus separately from one another, such 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 . - a main body , which is configured to be soft-elastic at least in part, and - a first fluid passage and a second fluid passage which each extend between an inlet side (A) and an outlet side (B) of the main body , - wherein the main body is configured in such a way and the fluid passages are arranged in such a way that, - in the event of a fluid overpressure between the inlet side (A) and the outlet side (B), the first fluid passage is freed by means of a fluid-overpressure-induced elastic deformation of the main body and the second fluid passage is sealed off in a fluid-tight manner, and, - in the event of a fluid underpressure between the inlet side (A) and the outlet side (B), the second fluid passage is freed by means of a fluid-underpressure-induced elastic deformation of the main body and the first fluid passage is sealed off in a fluid-tight manner, and, - in the event of a neutral fluid pressure between the inlet side (A) and the outlet side (B), the fluid passages are sealed off in a fluid-tight manner, - in the event of a fluid overpressure between the inlet side (A) and the outlet side (B), the first fluid passage is freed by means of a fluid-overpressure-induced elastic deformation of the main body and the second fluid passage is sealed off in a fluid-tight manner, and, - in the event of a fluid underpressure between the inlet side (A) and the outlet side (B), the second fluid passage is freed by means of a fluid-underpressure-induced elastic deformation of the main body and the first fluid passage is sealed off in a fluid-tight manner, and, - in the event of a neutral fluid pressure between the inlet side (A) and the outlet side (B), the fluid passages are sealed off in a fluid-tight manner, <EOS>