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 heavy load.

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.