Positive Crankcase Ventilation: Description and Operation

PCV System Operation:

The term "blow-by gas" stands for the compressed gas and exploded gas which blow through cylinder to piston clearance and contain a large amount of unburned gases such as CO and HC. The Positive Crankcase Ventilation (PCV) system is provided to prevent the blow-by-gas from being emitted into the atmosphere and it operates as follows:

^ When the vacuum in the intake manifold is low (throttle valve open), the PCV valve is wide open due to its spring force, thus more blow-by-gas is drawn into the intake manifold.

^ On the other hand, when the vacuum in the manifold is high, the PCV valve opening is limited due to the high vacuum, and the amount of the blow-by-gas drawn into the intake manifold is small.