the valve body. This will seal the crankcase from the
backfire which could otherwise cause an explosion.
The positive crankcase ventilation system can be
either the open or closed type (fig. 4-52).
The open type has an inlet breather that is open to
the atmosphere. When this system is used, it is possible
for a portion of the crankcase blow-by to escape through
the breather whenever the engine is under a sustained
The closed type has a sealed breather that is
connected to the air filter by a hose. Any blow-by gases
that escape from the breather when this system is used
will be aspirated into the carburetor and reburned.
Figure 4-52.PCV system.