Controlling the wastegate valve
The wastegate valve is acted on by a rod from the diaphragm box located on the compressor housing. A coil spring in the diaphragm box acts in a closing direction while the pressure of the diaphragm acts in an opening direction.
The engine management system supplies a solenoid valve with a PWM signal. The solenoid valve then allows pressure from the compressor to pass. When the pressure overcomes the spring force in the diaphragm box the rod will begin to move, opening the wastegate valve a corresponding amount. As the engine management system varies the PWM signal, the wastegate valve opening will change and the turbine speed can be regulated.