Overrun air recirculation control, function
One mechanical air recirculation valve -2- and -9- for each cylinder bank is located in a connecting pipe between intake side and pressure side of the two turbochargers -5- and -7-.
Mechanical air recirculation valves are opened by vacuum from Recirculating valve for turbocharger -N249- -item 8- when engine is on overrun or when idling or under part load. This disperses pressurized air (charge pressure) before throttle valve, and thus keeps turbochargers rotating at a higher speed.