Positive Crankcase Ventilation: Description and Operation

Fig. 11 Closed crankcase ventilation system.:

The closed crankcase ventilation system, Fig. 11, prevents blow-by gas from escaping into the atmosphere. The system controls these gases by directing them back into the intake manifold where they are consumed in the normal combustion process.
The crankcase ventilating air passes through a separate filter located in the air cleaner, then through a hose connecting the air cleaner and breather chamber. This air flows into the crankcase and combines with the crankcase vapors. This mixture flows through a passage in the cylinder block into the cylinder head and through the PCV valve.
The PCV valve contains a spring loaded plunger which is controlled by intake manifold vacuum. It increases blow-by gas flow in response to intake manifold vacuum.


The closed crankcase ventilation system prevents blow-by gas from escaping into the atmosphere. The system controls these gases by directing them back into the intake manifold where they are consumed in the normal combustion process. In addition, ventilating air is ducted into the crankcase to prevent pressure build-up.
System operation is regulated by a PCV valve. The PCV valve contains a spring loaded plunger which is controlled by intake manifold vacuum. The valve regulates suction of blow-by gasses in response to intake manifold vacuum.