The
normally closed solenoid valveis here, as in the case of all solenoid valves, a simple coil of wire that produces an electromagnetic field which, when activated, draws an armature (used as a pin to block the flow of vacuum through the valve) into its coil. These days, the process of an electric vacuum solenoid’s activation is usually governed by the action of an engine computer, rather than the engine vacuum itself. This allows for superior timing in terms of fuel delivery to the cylinders, which, again, means that more fuel can be burnt without any associated risk of igniting the contents of the fuel tank.
It’s not only in the exhaust gas recirculation system that you’ll find solenoids in your automobile. Indeed, electromechanical valves play an important part in many areas of most cars. Even starting your car requires you to activate the starter solenoid, a switch which, when it receives current from the ignition, draws two heavy metal contacts together. This opens the engine to the flow of electric current from the car battery, thus bringing the engine to life. If there’s not enough current supplied to the solenoid by the ignition, you’ll usually hear a weak, ‘clacking’ noise as the device repeatedly tries to close the contacts, despite lacking the requisite force to do so.