Exhaust Emissions System - Crankcase Ventilation: Operation

The primary circuit, connecting the PCV line to the intake manifold, contains a metal screen which separates the oil droplets from blow-by gases and a sonic jet which senses pressure differential and control volume of crankcase gases, thus preventing unbalance of idle air/fuel mixture.

The secondary circuit, PCV line to air cleaner, prevents entry of air into the crankcase and oil into the recirculation circuit at higher engine speeds. This is accomplished through a calibrated tube which limits crankcase vacuum when throttles are open. When the primary circuit (closed throttle) and the secondary circuit (open throttle) are in mid-range position, both circuits operate simultaneously.