EGR Valve: Description and Operation

The EGR valve is mounted on the intake manifold and controls exhaust gas flow into the intake manifold. The vacuum diaphragm chamber is connected to the carburetor flange vacuum port through the thermal vacuum valve. Opening the throttle valve applies a vacuum to the vacuum diaphragm. When the vacuum reaches a predetermined value, the diaphragm overcomes spring tension and moves to its fully raised position. The upward motion of the diaphragm opens the EGR valves allowing exhaust gas to be drawn into the engine intake system.