Blow-off valve

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The compressor bypass valve opens to prevent intense oscillations in the impeller when the throttle valve is suddenly closed (for instance, during gearchanges). This creates a circuit around the exhaust turbocharger. The compressor bypass valve prevents air from pulsating against the closed throttle valve.

The compressor bypass valve serves the following purposes:

Improved engine acoustic properties
Protects the exhaust turbocharger.

Additional effect: the exhaust turbocharger reacts quickly when the throttle valve is opened again. Without the blow-off valve, the exhaust turbocharger would work against the ram pressure of the closed throttle valve and become slower. On opening the throttle valve, the exhaust turbocharger would react with a delay.

The blow-off valve is attached to the exhaust turbocharger.

The blow-off valve is an electrical actuator controlled directly by the digital engine electronics (DME).

The compressor bypass valve is either open or closed, with no intermediate positions.