A gas distribution system for supplying a gas mixture to a plasma process chamber is provided. A first valve arrangement is connected to upstream ends of a first gas line and a second gas line. A second valve arrangement is connected to downstream ends of the first gas line and the second gas line. A first gas distribution outlet line is connected between a gas supply and the first valve arrangement and a first chamber inlet line connected between the second valve arrangement and the plasma process chamber. A first evacuation line is connected to the first gas line at a location between the first valve arrangement and the second valve arrangement. A second evacuation line is connected to the second gas line at a location between the first valve arrangement and the second valve arrangement. The first evacuation line and second evacuation line are in fluid communication with a vacuum line. A controller is operable to actuate the first valve arrangement and second valve arrangement to selectively flow the gas mixture from the gas supply to the plasma process chamber through the first gas line while the second gas is selectively evacuated by the vacuum line; or to selectively flow the gas mixture from the gas supply to the plasma process chamber through the second gas line while the first gas line is selectively evacuated by the vacuum line.