A valve mechanism (1) for dispensing a fluid, said valve mechanism being adapted in connection with the dispensing operation to open under the action of a positive pressure in the fluid and to close by itself when said positive pressure has ceased, comprising a channel (9) with an inlet (9a) and an outlet (9b) end and an axial direction of fluid flow (10), the channel (9) is defined by a body portion (11) of a rigid material formed with a groove (13) of substantially arcuate cross-section and by a cover portion (12) of flexible material whose side edges extending in the direction of the flow (10), wherein the cover portion (12) and body portion (11) are, along the side edges thereof, are sealingly connected to each other and wherein the cover portion (12) gradually conforms to the shape of the groove (13). A fixed sealing portion (20) is arranged of the outlet end (9b) of the channel (9) extending at least partially along a side wall (21 a, 21 b) of the groove (13).