Air valves are an important part to any mechanical ventilation system. Air (or control) valves are used for supply and exhaust of rather small quantities of air. Control/air valves are usually mounted directly in the air-duct system which has the advantage of not needing a plenum box. They are used in rooms where the ducting meets ceilings or walls so that air can be properly extracted or supplied. Air valves are adjustable and need to be set up during commissioning so that the correct air flow rate is reached. To adjust valves you simply rotate the central disc in or out to provide a larger or smaller air flow or insert a flow control damper.