Positive Crankcase Ventilation Valve: Description and Operation

The PCV valve is operated by the intake manifold vacuum. When the engine is running at idle the PCV valve is slightly opened and a small amount of blowby gas is drawn into the combustion chamber. At high engine speeds, the PCV valve is further opened and a larger amount of blowby gas is drawn into the combustion chamber. When deccelerating high manifold vacuum shuts the valve, and if an intake backfire occurs the valve shuts completely.