Positive Crankcase Ventilation: Description and Operation

Crankcase Ventilation System:

The PCV system is designed to prevent blow-by gases from being emitted into the atmosphere and is dependent upon a sealed engine. Blow-by gases are the result of the high pressures developed during the combustion process and contain undesirable pollutants. The primary control of this system is through the PCV Valve, which meters crankcase ventilation depending on intake manifold vacuum. The PCV Valve is a one-way check valve, located in the manifold valve cover or in line from the air cleaner to the valve cover.

When the engine is running, air from the air cleaner assembly is drawn into the crankcase and mixed with blow-by gases, through an attaching hose and filter. During engine idle, manifold vacuum is high and causes the PCV Valve to close against its internal spring. As the throttle valve opens and manifold vacuum weakens, spring force begins to regulate the PCV Valve opening. The air-diluted blow-by gases are then drawn into the intake manifold, becoming part of the calibrated air/fuel mixture.
If an abnormal operating condition develops (PCV Valve stuck closed), the system is designed to allow excessive amounts of blow-by gases in the crankcase to back flow into the air cleaner to be consumed by normal combustion.