Positive Crankcase Ventilation: Description and Operation

PCV Valve:

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