Function, low engine load

At low engine load, the pressure in the intake manifold is relatively low and a strong negative pressure predominates. The crankcase gases are passed from the oil trap via a duct in the cylinder head to a check valve fitted in the intake manifold. From the check valve the gases are passed through a duct which opens into the intake manifold. In the intake manifold the crankcase gases are mixed with the intake air and passed into the engine cylinders where they are burned.

Fig 1: Pressure Flow Diagram (Low Engine Load)

Courtesy of SAAB-SCANIA OF AMERICA, INC.