My limited understanding (and Johnny et al feel free to correct me) is that the main purpose is to allow blow-by gasses and pressure to escape; given that they have nasties from the combustion process (such as sulphur vapour) they are not considered environmentally friendly to just vent hence are put back into the intake to burn off oil droplets, nasties and general blowby fumes.
Also I understand that a bit of vacuum in the crank case helps the rings seal better for mo powaaaaa.
My 0.3L catch tank, which isn’t baffled, takes the crankcase pipe and the rocker cover pipe and has a filter on top. It fits just under the second intake on the airbox (originally designed to take air from over the top of the manifold for cold starting / warm up).
After 1200 miles or so of engine running in, thrashing about. I found it was a third full with what seemed to be “yellow water”. So unable to resist like any typical man, I dipped my finger in and gave it a taste. It was a full bodied and nutty flavour with a hint of Halvoline’s finest produce!
I hear that ideally you should aim for a baffled tank to better filter out the nasties and levitated micro oil drops, especially if you plan to feed through the intake again.
The filter is often steaming after a good thrash and eggy f@rty smells were common when previously I had it in a different position.
So have I missed anything fundamental about the operation of this circuit for non EFi cars?