Positive Crankcase Ventilation: Description and Operation

Positive Crankcase Ventilation System (PCV):

The PCV valve is operated by the intake manifold vacuum to prevent blowby gas from escaping to the atmosphere. When the engine is running at idle, the PCV valve is slightly opened and a small amount of blowby gas is drawn into the combustion chamber. At higher engine speeds the PCV valve is further opened and a large amount of blowby gas is drawn into the combustion chamber.