Valve device (1, 1a) for a medical fluid line system, with: - a main body (2, 2a), which is configured to be soft-elastic at least in part, and - a first fluid passage (3, 3a) and a second fluid passage (4, 4a) which each extend between an inlet side and an outlet side of the main body (2, 2a), - wherein the main body (2, 2a) is configured in such a way and the fluid passages (3, 3a, 4, 4a) are arranged in such a way that, - in the event of a fluid overpressure between the inlet side and the outlet side, the first fluid passage (3, 3a) is freed by means of a fluid-overpressure-induced elastic deformation of the main body (2, 2a) and the second fluid passage (4, 4a) is sealed off in a fluid-tight manner, and, - in the event of a fluid underpressure between the inlet side and the outlet side, the second fluid passage (4, 4a) is freed by means of a fluid-underpressure-induced elastic deformation of the main body (2, 2a) and the first fluid passage (3, 3a) is sealed off in a fluid-tight manner, and, - in the event of a neutral fluid pressure between the inlet side and the outlet side, the fluid passages (3, 3a, 4, 4a) are sealed off in a fluid-tight manner, wherein the main body (2, 2a) has a first wall portion (5, 5a) and a second wall portion (6, 6a) which are each elastically displaceable, under the effect of a fluid pressure, relative to a substantially dimensionally stable web portion (9, 9a) of the main body (2, 2a), characterized in that the wall portions (5, 5a, 6, 6a) are arranged on mutually opposite side faces (7, 7a, 8, 8a) of the web portion (9, 9a), thereby each forming one of the fluid passages (3, 3a, 4, 4a), and thus separately from one another, such that the first fluid passage (3, 3a) is substantially uninfluenced by a fluid-pressure-induced deformation of the second wall portion (6, 6a), and the second fluid passage (4, 4a) is substantially uninfluenced by a fluid-pressure-induced deformation of the first wall portion (5, 5a). - a main body (2, 2a), which is configured to be soft-elastic at least in part, and - a first fluid passage (3, 3a) and a second fluid passage (4, 4a) which each extend between an inlet side and an outlet side of the main body (2, 2a), - wherein the main body (2, 2a) is configured in such a way and the fluid passages (3, 3a, 4, 4a) are arranged in such a way that, - in the event of a fluid overpressure between the inlet side and the outlet side, the first fluid passage (3, 3a) is freed by means of a fluid-overpressure-induced elastic deformation of the main body (2, 2a) and the second fluid passage (4, 4a) is sealed off in a fluid-tight manner, and, - in the event of a fluid underpressure between the inlet side and the outlet side, the second fluid passage (4, 4a) is freed by means of a fluid-underpressure-induced elastic deformation of the main body (2, 2a) and the first fluid passage (3, 3a) is sealed off in a fluid-tight manner, and, - in the event of a neutral fluid pressure between the inlet side and the outlet side, the fluid passages (3, 3a, 4, 4a) are sealed off in a fluid-tight manner, - in the event of a fluid overpressure between the inlet side and the outlet side, the first fluid passage (3, 3a) is freed by means of a fluid-overpressure-induced elastic deformation of the main body (2, 2a) and the second fluid passage (4, 4a) is sealed off in a fluid-tight manner, and, - in the event of a fluid underpressure between the inlet side and the outlet side, the second fluid passage (4, 4a) is freed by means of a fluid-underpressure-induced elastic deformation of the main body (2, 2a) and the first fluid passage (3, 3a) is sealed off in a fluid-tight manner, and, - in the event of a neutral fluid pressure between the inlet side and the outlet side, the fluid passages (3, 3a, 4, 4a) are sealed off in a fluid-tight manner,