Hi Robin, Thanks for your reply.
Maybe ive just got this twisted but from what i can see the diagram show's how a recirculating system with a catch can works for a naturally aspirated car were the engine breathes into the airbox, in this system the gasses from the head/block still get passed into the inlet to be expelled minus any oil/carbon thanks to the catch can. Obviously this is not how the system works on our golfs due to the boost pressure in the inlet manifold, hence the reason for the 'PCV' system in the first place. Obviously the pressure inside the Block and head are higher than atmospheric due to blow-by, at the moment when this pressure is greater than in the inet manifold the 'PCV' alows the pressure to bleed of into the engine along with any oil/carbon.
By removing the 'PCV' and fitting a closed system such as the forge catch can the block breathes to the head and both breather lines from the head go to the catch can, The can does not vent to atmosphere so there is no way for the pressure to be releaved?
Hope this makes sense, it does in my head.