Abstract: A valve system for use in batch processing, particularly for preventing exposure of material to the environment during transfer from one container to another. The system in effect comprises two butterfly valve discs (5, 6; 105, 106), one (5; 105) on a container (12; 107) for transporting material to or from a reaction vessel (3; 103) and the other on the reaction vessel (3; 103) itself. Each valve disc (5, 6; 105, 106), when closed, shuts off the container (12; 107) or vessel (3; 103) respectively from the environment. When the container (12; 107) is connected to the vessel (3; 103) a shaft (9; 109) connected to one valve disc (5; 105) interengages with a shaft (10) connected to the other valve disc (6; 1006) to enable the discs (5, 6; 105, 106) to move simultaneously, and material may be transferred from the container (12; 107) to the vessel (3; 103) or vice versa.