Single Port (On-Off System)

The EGR system recirculates a small amount of exhaust gas into the intake system to reduce the combustion temperature and reduce the production of NOx. Exhaust gas is led from the the exhaust port of the No. 2 cylinder through a port in the cylinder head and then through a steel line to the EGR valve. When the EGR valve opens, a small amount of exhaust gas passes through the port and into the the intake manifold.

Fig. 65 Single Port EGR System:

The EGR valve is controlled by the vacuum created by the throttle plate. The relative position of the throttle to the vacuum outlet is designed so that the EGR valve will open at approximately 1900 RPM. The valve is fully open at low loads. When the intake manifold vacuum is low (full throttle) the vacuum is not strong enough to overcome the spring tension of the EGR valve, and therefor, the valve remains closed. The quantity of exhaust gas available for insertion to the intake is controlled by the orifice, as shown in Fig. 65.
The thermovalve is activated by engine coolant temperature and shuts off the flow of vacuum to the EGR valve when the engine coolant is below 100°F (43°C). This improves engine operation during cold operation by allowing a full fuel mixture to be present in the cylinder while the engine is warming up.