With accelerator released
- Vacuum in the intake manifold
- Throttle valve closed
- Charge air bypass valve open
When the throttle butterfly closes, a vacuum is quickly created in the intake manifold due to combustion while the overpressure before the throttle butterfly remains the same.
To prevent the pressure in the inlet manifold increasing too quickly, which will cause jerking, the excess pressure before the throttle butterfly valve must be released when the butterfly reopens.
Due to the vacuum in the inlet manifold, a vacuum is also obtained on the spring side of the charge air bypass valve. Since the bypass valve cannot resist the overpressure on the other side of the diaphragm by spring force alone, the valve opens and the overpressure from the delivery pipe and throttle housing is admitted to the intake manifold.