Abstract: A valve mechanism (2) for a re-fillable gas cartridge (1) comprising a body member (3) having a passage therethrough and adapted to engage in the neck of the cartridge. The passage comprises first and second bores (5, 6) extending from opposite ends of the body member and meeting at a step, the first bore having a diameter less than that of the second bore, the step defining a tapered valve seat (8). A valve member (10) having a head (10a) and a stem (10b) projecting therefrom is provided which is located in the passage so that the head of the valve member sealingly seats on the tapered valve seat with the stem located in the first bore. Means (11) are provided for biassing the valve member into its sealing postion.