mobile one.. all the others have this valve.. and when it gets filled up with gunk, it opens.. and lets ALL that junk that it collected out, into the oil stream... yea thats nooo goooood..
but the only problem is you have to change it.. other wise it will clog cuz there is no way to let it go.. and what happens when you starve a motor of oil???? yeaaa BOOOOM (maby).. but yea ..