A mixing manifold is provided. The manifold includes: a body; a first converging passageway in the body; a first diverging passageway in the body in-line and in fluid communication with the first converging passageway to form a first venturi; a first obstruction in a throat of the first venturi configured to move between two positions, a blocking position that blocks, at least in part, flow through the first venturi and an open position; a second converging passageway in the body; a second diverging passageway in the body in-line and in fluid communication with the second converging passageway to form a second venturi; and a second obstruction in the second venturi configured to move between two positions, a blocking position that blocks, at least in part, flow through the second venturi and an open position. A method of providing fluid flow through a manifold is also provided.