Positive Crankcase Ventilation: Description and Operation

Fig. 4 Positive Crankcase Ventilation (PCV) System:

The PCV system, Fig. 4, consists of a crankcase breather, a calibrated intake manifold jet and hose connected to the air cleaner. The crankcase breather is mounted on the side of the engine block and a filter screen is used to separate oil droplets from the crankcase vapors. The screen allows the oil droplets to return to the crankcase and also resists flow reversal in case of a backfire. During all modes of engine operation, the crankcase vapors flow through the breather tube. From there, vapors enter the intake manifold during low speed engine operation or enter the air cleaner during high speed operation. Both paths are used at intermediate speeds.