Positive Crankcase Ventilation: Description and Operation

Fig. 38 Typical positive crankcase ventilation system.:

PCV SYSTEM

A closed-type crankcase ventilation system, Fig. 38 is utilized to prevent blow-by gas from escaping into the atmosphere. This system uses a positive crankcase vent valve (PCV valve) at the rocker arm cover.

Fresh air is supplied to the crankcase through the air cleaner. Inside the crankcase fresh air is mixed with blow-by gases and this mixture passes through the PCV valve into the induction system.

The PCV valve has a metered orifice through which the mixture of fresh air and blow-by gases is drawn into the intake manifold in response to intake manifold vacuum. The valve capacity is adequate for all normal driving conditions. Under heavy acceleration crankcase vapors will backup into the air cleaner housing until engine operation returns to normal.

Fig. 26 PCV valve operation:

The PCV valve, Fig. 26 operates as a one way valve to help purge crankcase emissions from the crankcase.