So in these lovely MS paint drawings, that I am quite proud of, here's how the system operates under boost and vacuum. You'll have to imagine the VTA filter in place, as I didn't get any photos of the kit on our test car of it in place.
here's what the colors represent:
Green is vacuum flow, when the manifold is under vacuum
Red is boost flow, when the manifold is under boost
Yellow is crankcase pressure under boost
Orange circle is an open checkvalve
Orange X is a closed checkvalve
Vacuum:
Under vacuum the main checkvalve is open, and the manifold vacuum is pulling a vacuum on the crankcase. The VTA valve is closed, not allowing any un-metered air in.
Boost:
Under boost the boost from the manifold makes its way to the checkvalve where the valve is now closed and preventing boost into the OCC system. The pressure from the crankcase cracks open the PCV valve, makes it's way to the OCC and is then vented by the VTA valve which opens from the pressure as well. Total cracking pressure needed to open the PCV valve and the VTA valve is less than 0.5psi. It was hard to get a decent reading on this, as my gauge reads in incriminates of 1psi up to 60psi, but I barely got the needle to wiggle under the bottom mark.