Abstract: A gate valve is provided for returned drilling mud pressure control and/or well killing. The gate valve includes a flow passage; and a gate member movable for intersecting the flow passage. The gate member includes a gate port which extends from one face to an opposite face of the gate member and is alignable with the flow passage for allowing material in the flow passage to pass through the gate member, and a groove or recess is provided in an inner wall of the gate port, the groove or recess extending from the one face to the opposite face of the gate member. A method is provided for returned drilling mud pressure control and/or well killing, and uses of a gate valve.