See Figures 1, 2, 3, 4 and 5
The PCV system is designed to prevent blow-by gas from escaping to the atmosphere by drawing it directly into the intake manifold. The PCV valve contains a spring loaded plunger which is lifted in proportion to intake manifold vacuum. Under high vacuum, blow-by is returned directly to the manifold through the breather chamber and PCV valve with fresh air. When intake manifold vacuum decreases (wide open throttle) and vacuum in the air cleaner increases, the PCV valve closes and the blow-by is returned through the valve cover breather hose and into the air cleaner. The PCV valve also acts as a check valve when the engine backfires to prevent crankcase explosion.