Positive Crankcase Ventilation: Description and Operation

Crankcase Ventilation Flow:

PURPOSE
The Positive Crankcase Ventilation (PCV) system used to provide more complete scavenging of crankcase vapors.

OPERATION
Fresh air from the air cleaner, through a filter, is supplied to the crankcase, mixed with blow-by gases and then passed through the crankcase vent tube assembly into the intake manifold.

Crankcase Ventilation Valve Cross Section:

Primary control is through the Crankcase Ventilation Orifice which meters the flow at a rate depending on manifold vacuum. The Crankcase Ventilation Orifice meters the vacuum applied to the crankcase, and is a part of the crankcase vent tube assembly.
To maintain idle quality, the Crankcase Ventilation Orifice restricts the flow when intake manifold vacuum is high. If abnormal operating conditions arise, the system is designed to allow excessive amounts of blow-by gases to flow back through the crankcase vent hose into the air cleaner to be consumed by normal combustion.