Positive Crankcase Ventilation: Description and Operation

Positive Crankcase Ventilation (PCV) System:

PURPOSE
The Positive Crankcase Ventilation (PCV) System prevents blow-by gasses in the crankcase from escaping into the atmosphere.
The PCV valve is provided to conduct crankcase blow-by gas to the intake manifold.

OPERATION
During partial throttle operation of the engine, the intake manifold sucks the blow-by gas through the PCV valve.
Normally, the capacity of the valve is sufficient to handle any blow-by and a small amount of ventilating air.
The ventilating air is then drawn from the air duct, through the hose connecting air inlet tubes to rocker cover, into the crankcase.
Under full-throttle condition, the manifold vacuum is insufficient to draw the blow-by flow through the valve, and its flow goes through the hose connection in the reverse direction.
On vehicles with an excessively high blow-by some of the flow will go through the hose connection to the intake collector under all conditions.