The V8 Owners Forum -

Some oil filters are designed with an inbuilt pressure relief valve, brought into operation when the difference between the oil pressure entering the filter and that leaving the filter exceeds a pre determined level. Oil thus bypasses the filter media, returning to the engine unfiltered.

Other oil filters have no such inbuilt feature.

Of these two designs, is one preferable to use with the RV8, and if so why?
I note that there is a filter bypass inbuilt into the oil pump front covers, as fitted to the P6B. Does this make the use of the former and it's inbuilt relief valve redundant?

Ron.

I allways thought the Valve was a Non return, helping cars where the filter is in a silly position and drainback is a problem.

I believe the internal bypass in the filter is pretty crude and once it has opened it never closes again, it is there for when the filter becomes bunged up at the end of it's life it will allow oil to the rest of the system rather than starve it of oil alltogether. It is also a saftey if for some reason your normal press valve fails to open it stops the filter "bursting" internally and trying to push the filter medium into the oil ways of your engine.
As for which is best, depends what you are using it for for dry sump high pressure systems where there is more than one filter element and the pumps are checked and maintained frequently then non bypass ones are preffered, they are tougher and you don't have any risk og grot being bypassed into your oil ways.
For a fit and forget to the next oil change application then the bypass type are best.
Mike