Positive Crankcase Ventilation: Description and Operation

Fig. 6 Positive crankcase ventilation system.:

The engine blow-by gasses and crankcase vapors flow across the vent insert, Fig. 6, and connection fitting to the cyclone oil separator. They then flow through the air intake system and into the combustion chambers together with the intake air.
Oil separated in the cyclone oil separator flows through the return line and check valve back into the oil pan. The check valve ensures no oil vapors from the oil pan are drawn into the intake system by existing vacuum.