I've heard competing views on this and thought this would be a good place to open some discussion on it. My Subaru and many others have vertical oil filters on it (threads are at the top....probably obvious) that are relatively low compared to the bottom of the oil pan (not lower than the pan though, but in that realm....as in it's not 2ft above the bottom of the pan). With this configuration, why would you need an ADBV. I know that the early OEM subaru filters (the white purolator made ones equal to 14460) did not have an ADBV. Is the gist, that while the car is off, you don't want the 'column' of clean oil post outlet of the filter, to drain down, flow the opposite direction through the media and back into the pan such that on next start up, it has to recreate this column of oil since the outlet passage is empty? And just to make sure I am visualizing things correctly, does the oil pump draw oil out of the pan, through the pump, into the dirty 'side' of the filter and then out of the clean 'side'....or is the pump on the clean side? I'm actually embarrassed to say that after 10 years of working on my car(s), I don't know the oil flow schematics of a car.