Albert,
One of the other PCV systems I recall seeing used two tubes. Mostly found on V8 engines, though, on opposing valve covers.
One is hooked to the inside of the air filter chamber, with no valve. Other hose is plumbed to the inlet manifold itself.
The idea is that when the manifold vacuum is incapable of purging the vapours, they are drawn through the "free" line into the air filter's chamber, and as manifold vacuum increases, the PCV does its thing, and the unvalved line reverses flow, and merely provides a feed source of clean cooler air, helping keep temperatures down also.
Does this make some sense?
Regards, Adam.