If you look at the Mann and Mahle filters (among others) in this guy's oil filter deconstruction, you'll see where he refers to the anti-drainback valves.

As for the hatch struts, if one is appreciably stronger than the other it is going to wind up carrying the bulk of the load- only when it gets sinks or lowers down to the weaker strut's catch point is the weaker strut going to pick up part of the load. You can see how this period of working solo when it's supposed to be working in tandem could potentially shorten its life.

Robert

----- Original Message ----- From: "Tabe Johnson" <greentabe-vanagon@YAHOO.COM> To: <vanagon@GERRY.VANAGON.COM> Sent: Tuesday, August 29, 2006 9:34 PM Subject: Re: Re-useable oil filter

> Mike/List, > > This is a load of hokum that has been going 'round the list > for a while. The only valve in any oil filter is a bypass valve > which would activate itself if the filter media got too clogged to > pass enough oil, for instance. > > Let's see: How would a valve that kept the lifters from bleeding > down work? It would apply oil pressure. Where does oil pressure > come from? The oil pump. When the engine's off, the pump's off. > So when the engine's off, there's no oil pressure, regardless of > how many valves you have in your filter. > > tabe johnson/87 westy > > PS - speaking of hokum, (and I'm not trying to be aggressive - just > asking the question) how is it that replacing just one of the two > pneumatic rear hatch struts can cause it to fail prematurely? One > strut doesn't know what the other is doing. It's just applying > pressure to a piston, right? > > > > *** cut here *** > Date: Tue, 29 Aug 2006 21:58:33 -0400 > From: Mike Collum <collum@VERIZON.NET> > Subject: Re: Re-useable oil filter > > But what about the valve in the filter that keeps the lifters from > leaking down? > > Mike