By the way : that little widget can cause a lot trobles when faulty...
After fuel delivery problems, I (and Wingaman) changed my filter (wich was fine), removed my water separator (no change), changed hosesand even tank (thinking of probable sand-dust-whatever in thank). No change.
Always air in hose between filter and pump plus vacuum in pump.
Tough it could'ntbe the return vavle : would it have been the problem, I figured there woud be TOO MUCH pressure in filter, not a vaccum...
Finally,it was that damned valve (wich was brandnew -- replaced byprevention :? )
Back to the good old 1.6d filter (without return gestion). No more troubles.
(Excuse my english. I'm french too...)