Closed system to prevent vapours, gases and partially burned fuel mixture escaping from the crankcase into the atmosphere.

A system that draws fresh, filtered air through the crankcase to remove blowby gases. The gases are then pulled into the intake manifold to be reburned. The PCV valve controls the airflow so it will be stable, regardless of intake manifold vacuum. A malfunctioning PCV system can cause engine oil leaks and high crankcase pressure, mimicking more severe engine problems.

On all vehicles built since the late 1960s, the Crankcase Vapour Control System prevents crankcase vapours from escaping into the atmosphere. To do this, a regulated amount of vapour is introduced into the engine where it is burned. A key component in regulating this vapour is a PCV Valve or a PCV orifice.