Air Bypass Valve: Description and Operation

Air Cleaner, Air Piping And Components (Turbocharged):

PURPOSE
The Air Bypass Valve, is a vacuum controlled pressure relief valve. To prevent throttle overrun during sudden throttle closure, it is necessary to provide a bypass.
OPERATION
Pressurized air is bled off to the inlet side of the turbocharger by using surge tank vacuum (created any time the throttle is in the closed position) to open the valve.