A valve assembly includes a nitrogen enriched airflow control valve, a
first stage surge control valve and a second stage surge control valve
respectively arranged in a passage downstream of an air separation
module, and in first and second surge control passages. The valves are in
a ganged relationship or connected to one another such they move with one
another in response to an input from a common actuator. The surge control
valves open as the nitrogen enriched airflow control valve is moved to
provide a smaller area.