The pressure is higher in the case than in the intake path, so some of the block pressure is bled off by porting it into the intake (in my case). If it were just a pipe (no valve), the fuel/air mixture in the intake would be able to backflow into the block through the head if the pressure differential were shifted back (not sure how that would happen). Regardless, the PCV is a valve. By the way, I was never able to tell that the
oil was flowing into the intake before installing the separator. I tried installing an inline fuel filter in hopes it would catch some
oil residue, but it never did. The
oil is atomized in the air so well that only a proper filter system will trap it out.