A crankcase ventilation system is used to consume crankcase vapors created during the combustion process instead of venting them to atmosphere.

Fresh air is supplied through a filter to the crankcase, the crankcase mixes the fresh air with the blow-by gases and then passed through a positive crankcase ventilation (PCV) valve into the intake manifold.

The PCV valve controls the flow rate of the blow-by gases based on intake manifold vacuum. To maintain idle quality, the PCV valve (1) restricts the flow when inlet vacuum is high. If abnormal operating conditions arise, the system is designed to allow excessive amounts of blow-by gases to back flow through the crankcase vent tube into the throttle body in order to be consumed by normal combustion.