Positive Crankcase Ventilation: Description and Operation

Fig. 3 PCV Valve:

Intake manifold vacuum removes crankcase vapors and piston blow-by from the engine. The vapors pass through the PCV valve into the intake manifold where they become part of the calibrated air-fuel mixture. They are burned and expelled with the exhaust gases. The air cleaner supplies make up air when the engine does not have enough vapor or blow-by gases. In this system, fresh filtered air enters the crankcase.