Exhaust Gas Recirculation Valve
An (EGR) or exhaust gas recirculation valve is used on gasoline and diesel engines to reduce the amount of NOx or nitrogen oxides NO, and NO2 released into the atmosphere. When nitrogen and oxygen combine in high cylinder temperatures, this harmful gas forms.
The EGR valve reduces the amount of NOx by recirculating a small amount of exhaust into the intake through a controlled opening between the intake and the exhaust. By mixing this inert gas into the air-fuel charge, the cylinder's temperature is reduced. Reducing the temperature reduces the amount of NOx produced in the chamber.
It prevents the engine's cylinders from reaching damaging temperatures and protects the environment from smog resulting from excessive NOx production.
There are different types of EGR systems used on different engines. The vacuum operated EGR valve used in the illustration above is opened by vacuum supplied through a duty cycle solenoid and closed by a spring.