Thank you for you help.
I was to a local spares dealer, he identified the pipe after the van's identification number but the pipe I received is not the right one (the diameter is too small). The dealer don't knows what to do because in the catalog are no further information (as length, diameter or so). We have looked to the same picture as you sent me in your first link, we choose the no 5 pipe but...
I will give you some more information about the pipe maybe you can give me more details. So, on the filter assembly are three connection slots, 2 on the body and one on the cap. We are discussing about the pipe that connects on the body of the filter ( in the upper slot, the larger one).
Thank you again