The AIV is mounted on the inlet to the air compressor. It serves as the throttle controlling the compressor discharge pressure. Unlike the throttle on an engine which is an adjustable stationary valve the AIV is a modulating valve which is constantly opening and closing. It controls the air entering the compressor. More air allowed into the compressor equals more discharge pressure. The AIV is controlled by the air control circuit which has three different valves allowing for operation the three different modes.
When a CAF system is in operation, it sounds as though the system is rapidly throttling up and down on a constant or periodic cycle. What you are hearing is actually the AIV opening and closing to meet the air intake demands.
The AIV device has no firefighter adjustments. This unit should only be maintained by a qualified F-7 EVT Certified mechanic.
