Crankcase emission control equipment is separated into two different systems: Positive
Crankcase Ventilation (PVC) and Crankcase Ventilation System (CCV). The systems perform
the same function, differing only in the way the exhaust gases are metered. The PVC system uses
a valve, containing spring loaded plunger, which meters the amount of crankcase vapors routed
to the combustion chamber based on manifold vacuum. The CCV system contains a metered
orifice of a calibrated size which meters the amount of crankcase vapors drawn from the engine
based on manifold vacuum.
When the engine is running, a small portion of the gases which are formed in the combustion
chamber during combustion leak by the piston rings and enter the crankcase. Since these gases
are under pressure, they tend to escape from the crankcase and enter into the atmosphere. If these
gases were allowed to remain the the crankcase for any length of time, they would contaminate
the engine oil and cause sludge to build up. If the gases are allowed to escape into the
atmosphere, they would pollute the air, as they contain unburned hydrocarbons. The crankcase
emission control equipment recycles these gases back into the engine combustion chamber where
they are burned.
While the engine is running, clean filtered air is drawn into the crankcase either directly through
the oil filler cap, or through a filter mounted in the air cleaner assembly and connected to the oil
filler cap. As the air passes through the crankcase it picks up combustion gases, carries them out
of the crankcase, through the PCV valve, and into the intake manifold. After entering the intake
manifold gases are drawn into the combustion chamber and burned.

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