Positive Crankcase Ventilation: Description and Operation

PCV System Diagram:

The Positive Crankcase Ventilation ([1][2]PCV) system prevents the escape of blow-by gases from inside the crankcase into the atmosphere.

Fresh air is sent from the air cleaner into the crankcase through the breather hose, to be mixed with the blow-by gases inside the crankcase. The blow-by gas inside the crankcase is drawn into the intake manifold through the PCV valve.

The plunger inside the PCV valve is designed to lift according to intake manifold vacuum, regulating the flow of blow-by.

The blow-by gas flow is decreased during low load engine operation to maintain engine stability, and is increased during high load operation to improve the ventilation performance.