The system relies on the intake manifold's air pressure being less than crankcase air pressure. The lower pressure of the intake manifold pulls air from the breather through the valve, and into the intake manifold.
For the Smog Test: It is critical that the PCV system be clean, connected and un-plugged otherwise air flow to the intake manifold and subsequently the combustion chambers will be insufficient.
A plugged or malfunctioning PCV system will cause a smog check failure. PCV problems are primarily due to neglected maintenance and inadequate engine oil changes.
The hoses, filters and valve which this system consists of must be functioning and properly connected. It is pertinent that there be no cracks or leaks in with in the PCV system. Malfunctions of this sort will not only cause an emissions visual failure, but will increase tailpipe emissions as well.