I ordered a set of those Krank Vents from ET Performance -- you know, the chrome-looking, $100 check valves. At first I was skeptical and wondered what would make a check valve worth $100, but after fiddling with them for a minute or two it's obvious.
These valves provide positive, 100% closure when you blow against the check mechanism. The website says they will hold over 100psi but I didn't try hooking them up to the compressor since I have nothing on my car that will even come close to that. But when you flip them around and blow "with" the check mechanism they open right up and flow like there's nothing there at all.
That's a stark difference to other check valves -- these things clearly open under 1psi (it's hard for any of us to blow over 1psi) and I would speculate that they open closer to 0psi than they do to 1psi. This is perfect and exactly what we need in our PCV systems -- a valve that will open easily and close quickly under boost.
The $100 kit comes with two valves -- one that's supposed to sit between the intake manifold and the PCV and one that's supposed to come off the valve cover. The idea is that when under vacuum, the valve cover check is closed and the one on the manifold is open, allowing the manifold to draw a vacuum on the crankcase since theoretically the crankcase is fully sealed at that point. When in boost, the manifold valve closes and if any crankcase pressure is built, the valve cover check opens releasing the pressure.
Pretty neat system -- once I get the motor back in the car this will be one of the first things I play around with!