Diaphragm box
The diaphragm box is controlled through a hose from the turbocharger via a solenoid valve. A coil spring in the diaphragm box normally keeps the wastegate valve closed. When the engine management system wants to regulate the charge air pressure, it sends a PWM signal to the solenoid valve to open it. The charge air pressure via the hose from the turbocharger overcomes the force of the coil spring in the diaphragm box and the wastegate valve starts to open.