Blowoff valve

Throttle open, therefore the blowoff valve is shut

Throttle closed, air pushes the blowoff valve open (upwards)

A blowoff valve (also called dump valve or compressor bypass valve) is a pressure release system present in most petrol turbocharged engines. Blowoff valves are used to reduce pressure in the intake system as the throttle is closed, thus preventing compressor surge.^[1]