[vettestr]

As the guys have said it can be plumbed with or without but you must have system vented in some manor. If you do not vent or use suction to remove gasses from engine it will build pressure in crank case and cause leaking.

Be mindful of where you pick up vac in the manifold. Although a properly functioning PCV is not a vac leak it does consume vac and can lean out a cylinder at low RPM. The best source or location to tap into the manifold is near the carb/s or a large plenum area as it has a dampening affect. If you use the port on a single runner in the manifold near the head it pulls from that cylinder and not the common area of the manifold.

A PVC valve is as a hose with a built in valve that shutters on and off. The on time allows suction to remove a volume/unit of gasses so no pressure can build up in the crank case. The off time keeps it from causing the mixture of fuel and air from getting to much air making the mixture lean.