Crankcase Ventilation Systems: Operation

Air enters system through oil filler cap and is circulated through engine. After circulating through the engine air is returned to intake manifold through an exhaust tube which extends from the crankcase ventilation outlet in valve cover to a spring loaded regulator valve. This valve regulates amount of air to meet changing operating conditions. The regulator valve is controlled by intake manifold vacuum. During idle, intake manifold vacuum is high. This high vacuum overcomes tension of spring and seats valve. With valve in seated position, all ventilating air passes through a calibrated orifice in the valve, and there is minimum ventilation. As engine speed increases and manifold vacuum decreases, the spring forces valve off its seat and to full open position, which increases flow of ventilating air.