The invention provides a double disc gate valve where the discs are movable in a casing by a disc manipulation structure which can change an orientation of at least one of the valve discs relative to the center plane away from an initial orientation by movement of an outer disc carrier relative to an inner disc carrier. The relative movement between the disc carriers is initiated automatically during opening and closing of the valve. The change in orientation facilitates sealing between the discs and valve seats by a gradually established contact between the discs and the seats and the required opening and closing force may therefore be reduced.